View LTC3829EUHF-TRPBF_4566375.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

FeaTures
n n n n n n n n n n n n n n n n
LTC3829 3-Phase, Single Output Synchronous Step-Down DC/DC Controller with Diffamp DescripTion
The LTC(R)3829 is a high performance 3-phase single output synchronous step-down DC/DC switching controller that drives all N-channel synchronous power MOSFET stages. A constant frequency current mode architecture allows a phase-lockable frequency of up to 770kHz. Power loss and noise due to ESR of the input capacitors are minimized by operating the three controller output stages out of phase. The LTC3829 can be configured for 6-phase operation, has DCR temperature compensation, and output foldback current limiting. This device features a precision 0.6V reference and a power good indicator. Light load efficiency is optimized by using a choice of output Stage Shedding or Burst Mode operation. A differential amplifier provides true remote sensing of the output voltage at the point of load. The LTC3829 is available in both low profile 38-pin 5mm x 7mm QFN and Exposed Pad FE packages.
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP PolyPhase, Linear Technology, the Linear logo are , registered trademarks and Stage Shedding, No RSENSE are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 5705919, 5929620, 6144194, 6177787, 6580258, 6498466, 6674274, 6611136.
Optional Nonlinear Control for Fast Response 0.75%, 0.6V Reference Accuracy PWM, Stage SheddingTM or Burst Mode(R) Operation High Efficiency: Up to 95% RSENSE or DCR Current Sensing Programmable DCR Temperature Compensation Phase-Lockable Fixed Frequency: 250kHz to 770kHz True Remote Sense Differential Amplifier Programmable Active Voltage Positioning (AVP) Triple N-Channel MOSFET Synchronous Drive Wide VIN Range: 4.5V to 38V Operation VOUT Range: 0.6V to 5V without Diffamp VOUT Range: 0.6V to 3.3V with Diffamp Clock Input and Output for 6-Phase Operation Adjustable Soft-Start or VOUT Tracking 38-Pin (5mm x 7mm) QFN and FE Packages
applicaTions
n n n n
Notebook and Palmtop Computers Telecom Systems Portable Instruments DC Power Distribution Systems
Typical applicaTion
4.7F INTVCC VIN
+
TG1 SW1 BG1 PGND SENSE1+ SENSE1- TG2 0.6H 0.002
22F 35V 3
VIN 6V TO 28V
BOOST1 BOOST2 BOOST3 SW3 SW2 SW1 680pF
100
Efficiency
VIN = 12V 95 VOUT = 1.5V
16 14 12 POWER LOSS (W)
VIN EFFICIENCY (%) 0.6H 0.002 VOUT 1.2V 50A
90 85 80 75 70 65 60 0.002 55 50 0.1 1 10 LOAD CURRENT (A) POWER LOSS EFFICIENCY
100k
FREQ ITH TK/SS SGND DIFFOUT LTC3829
SW2 BG2
10 8 6 4 2 0 100
3829 TA01b
5k
0.1F
SENSE2+ SENSE2- TG3 SW3 BG3 SENSE3+ SENSE3-
VIN 0.6H
20k 20k VFB DIFFN DIFFP
+
COUT 470F 4V 4
3829 TA01
3829f
LTC3829 absoluTe MaxiMuM raTings (Note 1)
Input Supply Voltage (VIN) ......................... 40V to -0.3V Topside Driver Voltages (BOOSTn) ............ 46V to -0.3V Switch Voltage (SWn) ................................... 40V to -5V Boosted Driver Voltage (BOOSTn - SWn) .... 6V to -0.3V INTVCC, PGOOD, RUN, EXTVCC .................... 6V to -0.3V ITEMP IFAST, VFB Pin Voltages.............. INTVCC to -0.3V , TK/SS, FREQ, DIFFP DIFFN, DIFFOUT, ISET , AVP ILIM, MODE, PLLIN Voltages .......... INTVCC to -0.3V , ITH Voltage ............................................ INTVCC to -0.3V SENSE+n, SENSE-n................................... 5.7V to -0.3V Operating Junction Temperature Range (Notes 2, 3) ............................................ -45C to 125C Storage Temperature Range................... -65C to 125C Lead Temperature (Soldering, 10 sec) (FE) ........... 300C
pin conFiguraTion
TOP VIEW TOP VIEW DIFFOUT CLKOUT BOOST1 ITEMP MODE IFAST TG1 ITEMP DIFFOUT DIFFN DIFFP 31 SW1 30 BG1 29 BG2 28 SW2 27 TG2 39 26 BOOST2 25 VIN 24 INTVCC 23 EXTVCC 22 BG3 21 SW3 20 TG3 13 14 15 16 17 18 19 PGOOD PLLIN BOOST3 VFB ITH ISET ILIM RUN AVP SENSE1+ SENSE1- SENSE2+ 1 2 3 4 5 6 7 8 9 39 38 IFAST 27 MODE 36 CLKOUT 35 BOOST1 34 TG1 33 SW1 32 BG1 31 BG2 30 SW2 29 TG2 28 BOOST2 27 VIN 26 INTVCC 25 EXTVCC 24 BG3 23 SW3 22 TG3 21 BOOST3 20 PLLIN
38 37 36 35 34 33 32 DIFFN 1 DIFFP 2 RUN 3 AVP 4 SENSE1+ 5 SENSE1- 6 SENSE2+ 7 SENSE2- 8 TK/SS 9 FREQ 10 SENSE3+ 11 SENSE3- 12
SENSE2- 10 TK/SS 11 FREQ 12 SENSE3+ 13 SENSE3- 14 VFB 15 ITH 16 ISET 17 ILIM 18 PGOOD 19
UHF PACKAGE 38-LEAD (5mm 7mm) PLASTIC QFN TJMAX = 125C, JA = 34C/W EXPOSED PAD (PIN 39) IS SGND/PGND, MUST BE SOLDERED TO PCB
FE PACKAGE 38-LEAD PLASTIC TSSOP TJMAX = 125C, JA = 25C/W EXPOSED PAD (PIN 39) IS SGND/PGND, MUST BE SOLDERED TO PCB
3829f
LTC3829 orDer inForMaTion
LEAD FREE FINISH LTC3829EUHF#PBF LTC3829IUHF#PBF LTC3829EFE#PBF LTC3829IFE#PBF TAPE AND REEL LTC3829EUHF#TRPBF LTC3829IUHF#TRPBF LTC3829EFE#TRPBF LTC3829IFE#TRPBF
(Note 2)
PART MARKING* 3829 3829 LTC3829 LTC3829 PACKAGE DESCRIPTION 38-Lead (5mm x 7mm) Plastic QFN 38-Lead (5mm x 7mm) Plastic QFN 38-Lead Plastic TSSOP 38-Lead Plastic TSSOP TEMPERATURE RANGE -40C to 125C -40C to 125C -40C to 125C -40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
elecTrical characTerisTics
SYMBOL VIN VOUT VFB IFB VREFLNREG VLOADREG PARAMETER Input Voltage Range Output Voltage Range Regulated Feedback Voltage Feedback Current Reference Voltage Line Regulation Output Voltage Load Regulation
The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25C. VIN = 15V, VRUN = 5V, unless otherwise noted. (Note 2)
CONDITIONS MIN 4.5 0.6 ITH Voltage = 1.2V (Note 4) -40C to 85C l l ITH Voltage = 1.2V (Note 4) TJ = 125C (Note 4) VIN = 4.5V to 38V (Note 4) (Note 4) Measured in Servo Loop, ITH Voltage = 1.2V to 0.7V Measured in Servo Loop, ITH Voltage = 1.2V to 1.6V ITH = 1.2V, Sink/Source 5A (Note 4) (Note 5) VIN = 15V VRUN = 0V In Dropout, fOSC = 500kHz VINTVCC Ramping Down Measured at VFB Each Channel, VSENSE1,2,3 = 3.3V, VDIFFP = 3.3V VITEMP = 0.2V VTK/SS = 0V VRUN Rising VFB = 0.5V, VSENSE1,2,3 = 3.3V ILIM = 0V ILIM = Float ILIM = INTVCC VFB = 0.5V, VSENSE1,2,3 = 3.3V ILIM = 0V ILIM = Float ILIM = INTVCC
l l l
TYP
MAX 38 5.0
UNITS V V V V nA %/V % % mmho mA A % V V V A A A V mV
0.5955 0.593
0.600 0.600 -15 0.002 0.01 -0.01 2.2 4 40
0.6045 0.607 -50 0.02 0.1 -0.1
gm IQ DFMAX UVLO UVLO Hyst VOVL ISENSE1,2,3+ ITEMP ITK/SS VRUN VSENSE(MAX)
Transconductance Amplifier gm Input DC Supply Current Normal Mode Shutdown Maximum Duty Factor Undervoltage Lockout UVLO Hysteresis Feedback Overvoltage Lockout SENSE+ Pins Bias Current DCR Tempco Compensation Current Soft-Start Charge Current RUN Pin On Threshold RUN Pin On Hysteresis Maximum Current Sense Threshold (E-Grade)
60 3.6 0.68 2 11 1.5 1.35
93 3.0 0.64
94 3.3 0.6 0.66 1
l l l l l
9 1.0 1.1
10 1.25 1.22 100
l l l l l l
25 45 68 23 43 66
30 50 75 30 50 75
35 55 82 37 57 84
mV mV mV mV mV mV
Maximum Current Sense Threshold (I-Grade)
3829f
LTC3829 elecTrical characTerisTics
SYMBOL TG1,2,3 tr TG1,2,3 tf BG1,2,3 tr BG1,2,3 tf TG/BG t1D BG/TG t2D tON(MIN) VINTVCC VLDO INT VEXTVCC VLDO EXT VLDOHYS fNOM fLOW fHIGH RPLLN IFREQ IISET CLKOUT CLKHIGH CLKLOW PGOOD Output VPGL IPGOOD VPG PGOOD Voltage Low PGOOD Leakage Current PGOOD Trip Level, Either Controller IPGOOD = 2mA VPGOOD = 5V VFB with Respect to Set Output Voltage VFB Ramping Negative VFB Ramping Positive
l
The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25C. VIN = 15V, VRUN = 5V, unless otherwise noted. (Note 2)
PARAMETER TG Transition Time Rise Time Fall Time BG Transition Time Rise Time Fall Time CONDITIONS (Note 6) CLOAD = 3300pF CLOAD = 3300pF (Note 6) CLOAD = 3300pF CLOAD = 3300pF MIN TYP 25 25 25 25 30 30 90 4.8
l
MAX
UNITS ns ns ns ns ns ns ns
Top Gate Off to Bottom Gate On Delay CLOAD = 3300pF Each Driver Synchronous Switch-On Delay Time Bottom Gate Off to Top Gate On Delay CLOAD = 3300pF Each Driver Top Switch-On Delay Time Minimum On-Time Internal VCC Voltage INTVCC Load Regulation EXTVCC Switchover Voltage EXTVCC Voltage Drop EXTVCC Hysteresis Nominal Frequency Lowest Frequency Highest Frequency PLLIN Input Resistance Frequency Setting Current Shed and Burst Mode Program Current Phase (Relative to Controller 1) Clock High Output Voltage Clock Low Output Voltage Non-Shedding Mode Channel 2 and 3 Shedding 4 9 6.5 VFREQ = 1.2V VFREQ = 0V VFREQ 2.4V 450 210 700 (Note 7) 6V < VIN 38V ICC = 0mA to 20mA EXTVCC Ramping Positive ICC = 20mA, VEXTVCC = 5V 4.5
INTVCC Linear Regulator 5.0 0.5 4.7 50 200 500 250 770 100 10 7.5 60 180 5 0 0.1 0 -12 8 0.997 -10 10 1 80 2.5 100 3 INTVCC = 5V, IDIFFOUT = 300A (Note 8) (Note 8) VINTVCC - 1.4 VINTVCC - 1.1 3 2 0.2 0.3 2 -7 13 1.003 11 8.5 550 290 850 100 5.2 2.0 V % V mV mV kHz kHz kHz k A A Deg Deg V V V A % % V/V k mV dB mA V MHz V/s
3829f
Oscillator and Phase-Locked Loop
Differential Amplifier ADA RIN VOS PSRR ICL VOUT(MAX) GBW SR Gain Input Resistance Input Offset Voltage Power Supply Rejection Ratio Maximum Output Current Maximum Output Voltage Gain-Bandwidth Product Slew Rate Measured at DIFFP Input VDIFFP = VDIFFOUT = 1.5V, IDIFFOUT = 100A 5V < VIN < 38V
LTC3829 elecTrical characTerisTics
SYMBOL IFAST ISINK ISOURCE VAVP On-Chip Driver TG RUP TG RDOWN BG RUP BG RDOWN TG Pull-Up RDS(ON) TG Pull-Down RDS(ON) BG Pull-Up RDS(ON) BG Pull-Down RDS(ON) TG High TG Low BG High BG Low 2.6 1.5 4 1.1 PARAMETER Fast Transient Programmable Current Sink Current of AVP Pin Source Current of AVP Pin Maximum AVP Voltage Nonlinear Fast Transit Mode VIFAST = 400mV SENSE+ = 1.2V SENSE+ = 1.2V SENSE+ = 1.2V
l
The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25C. VIN = 15V, VRUN = 5V, unless otherwise noted. (Note 2)
CONDITIONS MIN 9 TYP 10 250 2 180 2.5 MAX 11 UNITS A A mA mV V
AVP (Active Voltage Positioning)
VAVP-VO(MAX) Maximum Voltage Drop VAVP to VO
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3829E is guaranteed to meet performance specifications from 0C to 85C operating junction temperature. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3829I is guaranteed to meet performance specifications over the full -40C to 125C operating junction temperature range. Note 3: TJ is calculated from the ambient temperature, TA, and power dissipation, PD, according to the following formula: LTC3829UHF: TJ = TA + (PD * 34C/W) LTC3829FE: TJ = TA + (PD * 25C/W)
Note 4: The LTC3829 is tested in a feedback loop that servos VITH to a specified voltage and measures the resultant VFB. Note 5: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. See Applications Information. Note 6: Rise and fall times are measured using 10% and 90% levels. Delay times are measured using 50% levels. Note 7: The minimum on-time condition corresponds to the on inductor peak-to-peak ripple current 40% of IMAX (see Minimum On-Time Considerations in the Applications Information section). Note 8: Guaranteed by design.
3829f
LTC3829 Typical perForMance characTerisTics
Load Step-Up (0A to 75A, 75A/s) (Nonlinear Operation) Load Step-Up (0A to 75A, 75A/s) (Normal Operation)
VOUT 100mV/DIV AC-COUPLED VSW1 10V/DIV VSW2 10V/DIV VSW3 10V/DIV
75mV
VOUT 100mV/DIV AC-COUPLED VSW1 10V/DIV VSW2 10V/DIV VSW3 10V/DIV 2s/DIV
3829 G01
95mV
2s/DIV
3829 G02
Phase Shedding Transition
Phase Shedding Transition
VSW1 10V/DIV VSW2 10V/DIV VSW3 10V/DIV
VSW1 10V/DIV VSW2 10V/DIV VSW3 10V/DIV
VIN = 12V
2s/DIV
3829 G03
VIN = 12V
2s/DIV
3829 G04
Prebiased Output at 2V
RUN 2V/DIV VOUT1 = 3.3V VOUT2 = 1.5V 1V/DIV
Coincident Tracking
VOUT 1V/DIV
VOUT1
VFB 500mV/DIV TK/SS 500mV/DIV VIN = 12V VOUT = 3.3V 2ms/DIV
3829 G05
VOUT2
VIN = 12V NO LOAD
2ms/DIV
3829 G06
3829f
LTC3829 Typical perForMance characTerisTics
5.5 5.3 5.1 SUPPLY CURRENT (mA) 4.9 4.7 4.5 4.3 4.1 3.9 3.7 3.5 4 24 14 INPUT VOLTAGE (V) 34 40
3829 G08
Quiescent Current vs Input Voltage without EXTVCC
5.25 5.00 4.75 4.50 4.25 4.00 3.75 3.50 3.25 3.00 2.75 2.50 2.25 2.00
INTVCC Line Regulation
Current Sense Threshold vs ITH Voltage
80 ILIM = INTVCC 60 ILIM = FLOAT VSENSE (mV) 40 20 ILIM = GND 0 -20 -40
INTVCC VOLTAGE (V)
0
5
10
15 20 25 30 INPUT VOLTAGE (V)
35
40
0
0.5
1 VITH (V)
1.5
2
3829 G10
3829 G09
Maximum Current Sense Threshold vs Common Mode Voltage
MAXIMUM CURRENT SENSE VOLTAGE (mV) 90 CURRENT SENSE THRESHOLD (mV) 80 70 60 50 40 30 20 10 0 0 4 3 2 VSENSE COMMON MODE VOLTAGE (V) 1 5 ILIM = GND ILIM = FLOAT ILIM = INTVCC 100 90 80 70 60 50 40 30 20 10 0
Maximum Current Sense Voltage vs Duty Cycle
MAXIMUM CURRENT SENSE VOLTAGE (mV) 100 90 80 70 60 50 40 30 20 10 0
Maximum Current Sense Voltage vs Feedback Voltage (Current Foldback)
ILIM = INTVCC
ILIM = INTVCC
ILIM = FLOAT ILIM = GND
ILIM = FLOAT ILIM = GND
0
10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%)
3829 G12
0
0.1
0.3 0.4 0.5 0.2 FEEDBACK VOLTAGE (V)
0.6
3829 G13
3829 G11
TK/SS Pull-Up Current vs Temperature
1.5 1.4
Shutdown (RUN) Threshold vs Temperature
TK/SS CURRENT (A)
RUN PIN VOLTAGE (V)
1.4
1.3 ON 1.2 OFF 1.1
1.3
1.2
1.1 -50
-25
75 0 25 50 TEMPERATURE (C)
100
125
1.0 -50
-25
0 25 50 75 TEMPERATURE (C)
100
125
3829 G14
3829 G15
3829f
LTC3829 Typical perForMance characTerisTics
Regulated Feedback Voltage vs Temperature
0.604 0.602 FREQUENCY (kHz) 0.600 VFB (V) 0.598 0.596 0.594 0.592 -50 -25 700 600 500 400 300 200 -50 -25 VFREQ = 0V 50 25 75 0 TEMPERATURE (C) 100 125 VFREQ = 1.2V VFREQ 2.4V UVLO THRESHOLD (V)
Oscillator Frequency vs Temperature
4.3 4.1 3.9 3.7 3.5 3.3 3.1 2.9 2.7
Undervoltage Lockout Threshold (INTVCC) vs Temperature
RISING
FALLING
50 25 75 0 TEMPERATAURE (C)
100
125
2.5 -50
-25
0 25 50 75 TEMPERATURE (C)
100
125
3829 G16
3829 G17
3829 G18
Oscillator Frequency vs Input Voltage
800 VFREQ 2.4V 600 FREQUENCY (kHz) VFREQ = 1.2V 400 VFREQ = 0V 200 SHUTDOWN CURRENT (A) 40 50
Shutdown Current vs Input Voltage
30
20
10
0
0
5
10
15 20 25 30 INPUT VOLTAGE (V)
35
40
0
5
10
25 15 30 20 INPUT VOLTAGE (V)
35
40
3829 G19
3829 G20
Shutdown Current vs Temperature
70 60 SHUTDOWN CURRENT (A) 50 40 30 20 10 0 -50 -25 QUIESCENT CURRENT (mA) 6 5 4 3 2 1
Quiescent Current vs Temperature without EXTVCC
50 25 75 0 TEMPERATURE (C)
100
125
0 -50 -25
50 25 75 0 TEMPERATURE (C)
100
125
3829 G21
3829 G22
3829f
LTC3829 pin FuncTions
(UHF/FE)
DIFFN (Pin 1/Pin 3): Negative Input of Remote Sensing Differential Amplifier. Connect this to the remote load ground pin. DIFFP (Pin 2/Pin 4): Positive Input of Remote Sensing Differential Amplifier. Connect this to the remote load positive terminal directly. RUN (Pin 3/Pin 5): Run Control Input. A voltage above 1.22V on this pin turns on the IC. There is a 1.0A pull-up current for this pin. Once the RUN pin rises above 1.22V, an additional 4.5A pull-up current is added to the pin. AVP (Pin 4/Pin 6): Active Voltage Positioning Load Slope Programming Pin. A resistor tied between this pin and the DIFFP pin sets the load slope. SENSE1+, SENSE2+, SENSE3+ (Pins 5, 7, 11/Pins 7, 9, 13): Current Sense Comparator Inputs. The (+) inputs to the current comparators are normally connected to DCR sensing networks or current sensing resistors. SENSE1-, SENSE2-, SENSE3- (Pins 6, 8, 12/Pins 8, 10, 14): Current Sense Comparator Inputs. The (-) inputs to the current comparators are connected to the output. TK/SS (Pin 9/Pin 11): Output Voltage Tracking and SoftStart Input. When one particular IC is configured to be the master of two ICs, a capacitor to ground at this pin sets the ramp rate for the master IC's output voltage. When the IC is configured to be the slave of two ICs, the VFB voltage of the master IC is reproduced by a resistor divider and applied to this pin. An internal soft-start current of 1.25A is charging this pin. FREQ (Pin 10/Pin 12): There is a precision 10A current sourced out of this pin. A resistor to ground sets a voltage which in turn programs the frequency. Alternatively, this pin can be driven with a DC voltage to vary the frequency of the internal oscillator. VFB (Pin 13/Pin 15): Error Amplifier Feedback Input. This pin receives the remotely sensed feedback voltage from an external resistive divider. ITH (Pin 14/Pin 16): Current Control Threshold and Error Amplifier Compensation Point. Each associated channels' current comparator tripping threshold increases with this ITH control voltage.
ISET (Pin 15/Pin 17): Stage Shedding Comparator and Burst Mode Comparator Programming Pin. A resistor to ground programs the stage shedding comparator threshold or Burst Mode comparator threshold and its current limit depending on MODE pin setting. ILIM (Pin 16/Pin 18): Current Comparator Sense Voltage Range Pin. This pin is to be programmed to SGND, FLOAT or INTVCC to set the maximum current sense threshold to one of three different levels for each comparator. PGOOD (Pin 17/Pin 19): Power Good Indicator Output. Open-drain logic out that is pulled to ground when the output exceeds 10% regulation window after the internal 100s power bad mask timer expires. PLLIN (Pin 18/Pin 20): External Synchronization Pin. A clock on the pin synchronizes the internal oscillator with the clock on this pin. EXTVCC (Pin 23/Pin 25): External Power Input to an Internal Switch Connected to INTVCC. This switch closes and supplies the IC power, bypassing the internal low dropout regulator, whenever EXTVCC is higher than 4.7V. Do not exceed 6V on this pin and ensure VIN > VEXTVCC at all times. INTVCC (Pin 24/Pin 26): Internal 5V Regulator Output. The control circuits are powered from this voltage. Decouple this pin to PGND with a minimum of 4.7F low ESR tantalum or ceramic capacitor. VIN (Pin 25/Pin 27): Main Input Supply. Decouple this pin to PGND with a capacitor (0.1F to 1F). BG1, BG2, BG3 (Pins 30, 29, 22/Pins 32, 31, 24): Bottom Gate Driver Outputs. These pins drive the gates of the bottom N-channel MOSFETs between PGND and INTVCC. SW1, SW2, SW3 (Pins 31, 28, 21/Pins 33, 30, 23): Switch Node Connections to Inductors. Voltage swing at these pins is from a Schottky diode (external) voltage drop below ground to VIN. TG1, TG2, TG3 (Pins 32, 27, 20/Pins 34, 29, 22): Top Gate Driver Outputs. These are the outputs of floating drivers with a voltage swing equal to INTVCC superimposed on the switch nodes voltages.
3829f
LTC3829 pin FuncTions
(UHF/FE)
BOOST1, BOOST2, BOOST3 (Pins 33, 26, 19/Pins 35, 28, 21): Boosted Floating Driver Supplies. The (+) terminal of the bootstrap capacitors connect to these pins. These pins swing from a diode voltage drop below INTVCC up to VIN + INTVCC. CLKOUT (Pin 34/Pin 36): Clock Output Pin. CLKOUT is 60 out of phase relative to channel 1 in non-shedding mode. During stage shedding, CLKOUT is 180 out of phase with channel 1. MODE (Pin 35/Pin 37): Forced Continuous Mode, Burst Mode or Shed Mode Selection Pin. Connect this pin to SGND to force IC in continuous mode of operation. Connect to INTVCC to enable shed mode operation. Leave the pin floating to enable Burst Mode operation. IFAST (Pin 36/Pin 38): Programmable Pin for Nonlinear Control Trip Threshold. A resistor to ground programs the tripping threshold for nonlinear control circuit. Connect this pin to INTVCC to disable this feature. See Applications Information section for details.
ITEMP (Pin 37/Pin 1): Input of the Temperature Sensing Comparator. Connect this pin to external NTC resistors placed near inductors. DIFFOUT (Pin 38/Pin 2): Output of Remote Sensing Differential Amplifier. Connect this pin to VFB through a resistive divider. SGND/PGND (Exposed Pad Pin 39/Exposed Pad Pin 39): Combined Signal and Power Ground Pad. Connect this pad closely to the sources of the bottom N-channel MOSFETs, the (-) terminal of CVCC and the (-) terminal of CIN. All small-signal components and compensation components should also Kelvin-connect to this pad.
3829f
0
LTC3829 FuncTional DiagraM
MODE PLLIN ITEMP EXTVCC 4.7V FREQ MODE/SYNC DETECT TEMPSNS 0.6V
-
F
+
VIN
+
5V REG INTVCC
VIN CIN
-
PLL-SYNC F
+
INTVCC BOOST BURSTEN TG SW SENSE+ SENSE- DB L1 VOUT CB M1
CLKOUT
OSC S RQ 3k
FCNT ON SWITCH LOGIC AND ANTISHOOTTHROUGH RUN
ICOMP
IFAST IFAST ILIM
SLOPE COMPENSATION
INTVCC 1 51k ITHB
SLOPE RECOVERY ACTIVE CLAMP SHED COMP ISET EA ISET
SLEEP
VIN 0.6V REF
0.5V
1.22V 1.0A
0.55V ISET ISET ITH RC CC1 RUN TK/SS CSS
+
-
+
-
-++
+
OV UVLO SS RUN
-
-
IREV
+
BG M2 PGND PGOOD DIFFOUT CVCC
+
COUT
RAVP
+
UV
0.54V VFB R2
+
DIFFAMP
40k 40k
DIFFP
- +
OV
-
40k 40k DIFFN
R1 0.66V SGND RPRE-AVP
-
1.25A
AVP
+ - + - + -
SENSE1+ SENSE1- SENSE2+ SENSE2- SENSE3+ SENSE3-
3829 BD
+
-
3829f
LTC3829 operaTion (Refer to Functional Diagram)
Main Control Loop The LTC3829 uses a constant frequency, current mode step-down architecture. During normal operation, each top MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when the main current comparator, ICMP , resets each RS latch. The peak inductor current at which ICMP resets the RS latch is controlled by the voltage on the ITH pin, which is the output of the error amplifier, EA. The remote sense amplifier (DIFFAMP) produces a signal equal to the differential voltage sensed across the output capacitor and re-references it to the local IC ground reference. The VFB pin receives a portion of this feedback signal and compares it to the internal 0.6V reference. When the load current increases, it causes a slight decrease in the VFB pin voltage relative to the 0.6V reference, which in turn causes the ITH voltage to increase until each inductor's average current equals one-third of the new load current (assuming all three current sensing resistors are equal). After each top MOSFET has turned off, the bottom MOSFET is turned on until either the inductor current starts to reverse, as indicated by the reverse current comparator, IREV , or the beginning of the next cycle. The main control loop is shut down by pulling the RUN pin low. Releasing RUN allows an internal 1.0A current source to pull up the RUN pin. When the RUN pin reaches 1.22V, the main control loop is enabled and the IC is powered up. When the RUN pin is low, all functions are kept in a controlled state. INTVCC/EXTVCC Power Power for the top and bottom MOSFET drivers and most other internal circuitry is derived from the INTVCC pin. When the EXTVCC pin is left open or tied to a voltage less than 4.7V, an internal 5V linear regulator supplies INTVCC power from VIN. If EXTVCC is taken above 4.7V, the 5V regulator is turned off and an internal switch is turned on connecting EXTVCC. Using the EXTVCC pin allows the INTVCC power to be derived from a high efficiency external source such as a switching regulator output. Each top MOSFET driver is biased from the floating bootstrap capacitor, CB, which normally recharges during each off cycle through an external diode when the top MOSFET turns off. If the input voltage, VIN, decreases to a voltage close to VOUT , the loop may enter dropout and attempt to turn on the top MOSFET continuously. The dropout detector detects this and forces the top MOSFET off for about one-twelfth of the clock period plus 100ns every third cycle to allow CB to recharge. However, it is recommended that a load be present or the IC operates at low frequency during the dropout transition to ensure CB is recharged. Shutdown and Start-Up (RUN and TK/SS Pins) The LTC3829 can be shut down using the RUN pin. Pulling the RUN pin below 1.22V shuts down the main control loop for the controller and most internal circuits, including the INTVCC regulator. Releasing the RUN pin allows an internal 1.0A current to pull up the pin and enable the controller. Alternatively, the RUN pin may be externally pulled up or driven directly by logic. Be careful not to exceed the absolute maximum rating of 6V on this pin. The start-up of the controller's output voltage, VOUT , is controlled by the voltage on the TK/SS pin. When the voltage on the TK/SS pin is less than the 0.6V internal reference, the LTC3829 regulates the VFB voltage to the TK/SS pin voltage instead of the 0.6V reference. This allows the TK/SS pin to be used to program a soft-start by connecting an external capacitor from the TK/SS pin to SGND. An internal 1.25A pull-up current charges this capacitor, creating a voltage ramp on the TK/SS pin. As the TK/SS voltage rises linearly from 0V to 0.6V (and beyond), the output voltage, VOUT , rises smoothly from zero to its final value. Alternatively, the TK/SS pin can be used to cause the start-up of VOUT to track that of another supply. Typically, this requires connecting to the TK/SS pin an external resistor divider from the other supply to ground (see the Applications Information section). When the RUN pin is pulled low to disable the controller, or when INTVCC drops below its undervoltage lockout threshold of 3.3V, the TK/SS pin is pulled low by an internal MOSFET. When in undervoltage lockout, all phases of the controller are disabled and the external MOSFETs are held off.
3829f
LTC3829 operaTion (Refer to Functional Diagram)
Light Load Current Operation (Burst Mode Operation, Stage Shedding or Continuous Conduction) The LTC3829 can be enabled to enter high efficiency Burst Mode operation, Stage Shedding mode or forced continuous conduction mode. To select forced continuous operation, tie the MODE pin to a DC voltage below 0.6V (e.g., SGND). To select Stage Shedding mode of operation, tie the MODE pin to INTVCC. To select Burst Mode operation, float the MODE pin. When the controller is enabled for Burst Mode operation, the peak current in the inductor is set to approximately one-sixth of the maximum sense voltage even though the voltage on the ITH pin indicates a lower value. The peak current can be programmed through the ISET pin. If the average inductor current is higher than the load current, the error amplifier, EA, will decrease the voltage on the ITH pin. When the ITH voltage drops below 0.5V (can also be programmed by the ISET pin), the internal sleep signal goes high (enabling sleep mode) and the external MOSFETs are turned off. In sleep mode, the load current is supplied by the output capacitor. As the output voltage decreases, the EA's output begins to rise. When the output voltage drops enough, the sleep signal goes low, and the controller resumes normal operation by turning on the top external MOSFET on the next cycle of the internal oscillator. When a controller is enabled for Burst Mode operation, the inductor current is not allowed to reverse. The reverse current comparator, IREV , turns off the bottom external MOSFET just before the inductor current reaches zero, preventing it from reversing and going negative. Thus, the controller operates in discontinuous operation. In forced continuous operation, the inductor current is allowed to reverse at light loads or under large transient conditions. The peak inductor current is determined by the voltage on the ITH pin. In this mode, the efficiency at light loads is lower than in Burst Mode operation. However, continuous mode has the advantages of lower output ripple and less interference with audio circuitry. When the MODE pin is connected to INTVCC, the LTC3829 operates in Stage Shedding mode at light loads. The controller will turn off channels 2 and 3 and increase the current gain of the first channel to ensure smooth transition. The threshold where the controller goes into Stage Shedding mode is when the ITH voltage drops below 0.5V, but it can be programmed by ISET pin. The inductor current is not allowed to reverse in this mode (discontinuous operation). At very light loads, the current comparator may remain tripped for several cycles and force the external top MOSFET to stay off for the same number of cycles (i.e., skipping pulses). This mode exhibits low output ripple as well as low audio noise and reduced RF interference as compared to Burst Mode operation. It provides higher low current efficiency than forced continuous mode, but not nearly as high as Burst Mode operation. 2-Chip Operations (CLKOUT Pin) The LTC3829's three channels are 120 out of phase providing multiphase operation. This configuration can provide enough power for most high current applications. However, for even higher power applications, the LTC3829 can be configured for PolyPhase(R) and 2-chip operation. The LTC3829 features a CLKOUT pin which enables two LTC3829s to operate out of phase. The CLKOUT signal is 60 out of phase with respect to phase 1 of the controller. In Stage Shedding mode, however, the CLKOUT signal is 180 out of phase with respect to phase 1 of the controller. Frequency Selection and Phase-Locked Loop (FREQ and PLLIN Pins) The selection of switching frequency is a trade-off between efficiency and component size. Low frequency operation increases efficiency by reducing MOSFET switching losses, but requires larger inductance and/or capacitance to maintain low output ripple voltage. If the PLLIN pin is not being driven by an external clock source, the FREQ pin can be used to program the controller's operating frequency from 250kHz to 770kHz. There is a precision 10A current flowing out of the FREQ pin so that the user can program the controller's switching frequency with a single resistor to SGND. A curve is provided later in the Applications Information section showing the relationship between the voltage on the FREQ pin and switching frequency.
3829f
LTC3829 operaTion (Refer to Functional Diagram)
A phase-locked loop (PLL) is available on the LTC3829 to synchronize the internal oscillator to an external clock source that is connected to the PLLIN pin. The PLL loop filter network is integrated inside the LTC3829. The phaselocked loop is capable of locking any frequency within the range of 250kHz to 770kHz. The frequency setting resistor should always be present to set the controller's initial switching frequency before locking to the external clock. The controller is operating in forced continuous mode when it is synchronized. Sensing the Output Voltage with a Differential Amplifier The LTC3829 includes a low offset, unity-gain, high bandwidth differential amplifier for applications that require true remote sensing. Sensing the load across the load capacitors directly greatly benefits regulation in high current, low voltage applications, where board interconnection losses can be a significant portion of the total error budget. The LTC3829 differential amplifier has a typical output slew rate of 2V/s. The amplifier is configured for unity gain, meaning that the difference between DIFFP and DIFFN is translated to DIFFOUT, relative to SGND. Care should be taken to route the DIFFP and DIFFN PCB traces parallel to each other all the way to the terminals of the output capacitor or remote sensing points on the board. In addition, avoid routing these sensitive traces near any high speed switching nodes in the circuit. Ideally, the DIFFP and DIFFN traces should be shielded by a low impedance ground plane to maintain signal integrity. The maximum output voltage when using the differential amplifier is INTVCC - 1.4V (typically 3.6V). Above this output voltage the differential amplifier should not be used. Power Good (PGOOD Pin) The PGOOD pin is connected to an open drain of an internal N-channel MOSFET. The MOSFET turns on and pulls the PGOOD pin low when the VFB pin voltage is not within 10% of the 0.6V reference voltage. The PGOOD pin is also pulled low when the RUN pin is below 1.22V or when the LTC3829 is in the soft-start or tracking phase. When the VFB pin voltage is within the 10% regulation window, the MOSFET is turned off and the pin is allowed to be pulled up by an external resistor to a source of up to 6V. The PGOOD pin will flag power good immediately when the VFB pin is within the regulation window. However, there is an internal 100s power-bad mask when the VFB goes out of the window. Output Overvoltage Protection An overvoltage comparator, OV, guards against transient overshoots (>10%) as well as other more serious conditions that may overvoltage the output. In such cases, the top MOSFET is turned off and the bottom MOSFET is turned on until the overvoltage condition is cleared. Undervoltage Lockout The LTC3829 has two functions that help protect the controller in case of undervoltage conditions. A precision UVLO comparator constantly monitors the INTVCC voltage to ensure that an adequate gate-drive voltage is present. It locks out the switching action when INTVCC is below 3.3V. To prevent oscillation when there is a disturbance on the INTVCC, the UVLO comparator has 600mV of precision hysteresis. Another way to detect an undervoltage condition is to monitor the VIN supply. Because the RUN pin has a precision turn-on reference of 1.22V, one can use a resistor divider to VIN to turn on the IC when VIN is high enough. An extra 4.5A of current flows out of the RUN pin once the RUN pin voltage passes 1.22V. The RUN comparator itself has about 80mV of hysteresis. One can program additional hysteresis for the RUN comparator by adjusting the values of the resistive divider. For accurate VIN undervoltage detection, VIN needs to be higher than 4.5V.
3829f
LTC3829 applicaTions inForMaTion
The Typical Application on the first page of this data sheet is a basic LTC3829 application circuit. The LTC3829 can be configured to use either DCR (inductor resistance) sensing or low value resistor sensing. The choice between the two current sensing schemes is largely a design trade-off between cost, power consumption and accuracy. DCR sensing is becoming popular because it saves expensive current sensing resistors and is more power efficient, especially in high current applications. However, current sensing resistors provide the most accurate current limits for the controller. Other external component selection is driven by the load requirement, and begins with the selection of RSENSE (if RSENSE is used) and inductor value. Next, the power MOSFETs are selected. Finally, input and output capacitors are selected. Current Limit Programming The ILIM pin is a tri-level logic input which sets the maximum current limit of the controller. When ILIM is either grounded, floated or tied to INTVCC, the typical value for the maximum current sense threshold will be 30mV, 50mV or 75mV, respectively. Which setting should be used? For the best current limit accuracy, use the 75mV setting. The 30mV setting will allow for the use of very low DCR inductors or sense resistors, but at the expense of current limit accuracy. The 50mV setting is a good balance between the two. SENSE+ and SENSE- Pins The SENSE+ and SENSE- pins are the inputs to the current comparators. The common mode input voltage range of the current comparators is 0V to 5V. All SENSE+ pins are high impedance inputs with small currents of less than 1A. The high impedance inputs to the current comparators allow accurate DCR sensing. All SENSE- pins and DIFFP should be connected to VOUT directly when DCR sensing is used. Care must be taken not to float these pins during normal operation. Filter components mutual to the sense lines should be placed close to the LTC3829, and the sense lines should run close together to a Kelvin connection underneath the current sense element (shown in Figure 1). Sensing current elsewhere can effectively add parasitic inductance and capacitance to the current sense element, degrading the information at the sense terminals and making the programmed current limit unpredictable. If DCR sensing is used (Figure 2b), sense resistor R1 should be placed close to the switching node, to prevent noise from coupling into sensitive small-signal nodes. The capacitor C1 should be placed close to the IC pins.
TO SENSE FILTER, NEXT TO THE CONTROLLER
3829 F01
COUT
RSENSE
Figure 1. Sense Lines Placement with Sense Resistor
Low Value Resistors Current Sensing A typical sensing circuit using a discrete resistor is shown in Figure 2a. RSENSE is chosen based on the required output current. The current comparator has a maximum threshold VSENSE(MAX) determined by the ILIM setting. The input common mode range of the current comparator is 0V to 5V. The current comparator threshold sets the peak of the inductor current, yielding a maximum average output current IMAX equal to the peak value less half the peak-to-peak ripple current, IL. To calculate the sense resistor value, use the equation: RSENSE = VSENSE(MAX ) I IMAX + L 2
Because of possible PCB noise in the current sensing loop, the AC current sensing ripple of VSENSE = IL * RSENSE also needs to be checked in the design to get a good signal-to-noise ratio. In general, for a reasonably good PCB layout, a 10mV VSENSE voltage is recommended as a conservative number to start with, either for RSENSE or DCR sensing applications. For previous generation current mode controllers, the maximum sense voltage was high enough (e.g., 75mV for the LTC1628/LTC3728 family) that the voltage drop across the parasitic inductance of the sense resistor represented a relatively small error. For today's highest current density solutions, however, the value of the sense resistor can be less than 1m and the
3829f
LTC3829 applicaTions inForMaTion
VIN INTVCC BOOST TG LTC3829 SW BG PGND SENSE+ SENSE- SGND RF CF RF
3829 F02a
VIN
SENSE RESISTOR PLUS PARASITIC INDUCTANCE RS ESL VOUT
CF * 2 * RF ESL/RS POLE-ZERO CANCELLATION
FILTER COMPONENTS PLACED NEAR SENSE PINS
(2a) Using a Resistor to Sense Current
VIN INTVCC BOOST OPTIONAL TEMP COMP NETWORK TG SW LTC3829 ITEMP RS BG PGND SENSE+ RNTC RP SENSE- SGND L R2 R = DCR *PLACE C1 NEAR SENSE+, R1||R2 x C1 = DCR SENSE(EQ) R1 + R2 - PINS SENSE **PLACE R1 NEXT TO INDUCTOR C1* R1** R2 VIN
INDUCTOR L DCR VOUT
3829 F02b
(2b) Using the Inductor DCR to Sense Current Figure 2. Two Different Methods of Sensing Current
peak sense voltage can be as low as 20mV. In addition, inductor ripple currents greater than 50% with operation up to 1MHz are becoming more common. Under these conditions the voltage drop across the sense resistor's parasitic inductance is no longer negligible. A typical sensing circuit using a discrete resistor is shown in Figure 2a. In previous generations of controllers, a small RC filter placed near the IC was commonly used to reduce the effects of capacitive and inductive noise coupled in the sense traces on the PCB. A typical filter consists of two series 10 resistors connected to a parallel 1000pF capacitor,
resulting in a time constant of 20ns. This same RC filter, with minor modifications, can be used to extract the resistive component of the current sense signal in the presence of parasitic inductance. For example, Figure 3 illustrates the voltage waveform across a 2m sense resistor with a 2010 footprint for the 1.2V/15A converter operating at 100% load. The waveform is the superposition of a purely resistive component and a purely inductive component. It was measured using two scope probes and waveform math to obtain a differential measurement. Based on additional measurements of the inductor ripple current
3829f
LTC3829 applicaTions inForMaTion
and the on-time and off-time of the top switch, the value of the parasitic inductance was determined to be 0.5nH using the equation: ESL = VESL(STEP) tON * tOFF IL tON + tOFF (1) where IMAX < 10A, set RF to 10 and CF to 1000pF This . will provide a good starting point. The filter components need to be placed close to the IC. The positive and negative sense traces need to be routed as a differential pair and Kelvin connected to the sense resistor. Inductor DCR Sensing For applications requiring the highest possible efficiency at high load currents, the LTC3829 is capable of sensing the voltage drop across the inductor DCR, as shown in Figure 2b. The DCR of the inductor represents the small amount of DC winding resistance of the copper, which can be less than 1m for today's low value, high current inductors. In a high current application requiring such an inductor, conduction loss through a sense resistor would cost several points of efficiency compared to DCR sensing. If the external R1|| R2 * C1 time constant is chosen to be exactly equal to the L/DCR time constant, the voltage drop across the external capacitor is equal to the drop across the inductor DCR multiplied by R2/(R1 + R2). R2 scales the voltage across the sense terminals for applications where the DCR is greater than the target sense resistor value. To properly dimension the external filter components, the DCR of the inductor must be known. It can be measured using a good RLC meter, but the DCR tolerance is not always the same and varies with temperature; consult the manufacturers' data sheets for detailed information. Using the inductor ripple current value from the Inductor Value Calculation section, the target sense resistor value is: RSENSE(EQUIV ) = VSENSE(MAX ) I IMAX + L 2
If the RC time constant is chosen to be close to the parasitic inductance divided by the sense resistor (L/R), the resulting waveform looks resistive again, as shown in Figure 4. For applications using low maximum sense voltages, check the sense resistor manufacturer's data sheet for information about parasitic inductance. In the absence of data, measure the voltage drop directly across the sense resistor to extract the magnitude of the ESL step and use Equation 1 to determine the ESL. However, do not overfilter. Keep the RC time constant, less than or equal to the inductor time constant to maintain a high enough ripple voltage of VSENSE. The above generally applies to high density/high current applications where IMAX > 10A and low values of inductors are used. For applications
VSENSE 20mV/DIV
VESL(STEP)
500ns/DIV
3829 F03
Figure 3. Voltage Waveform Measured Directly Across the Sense Resistor
VSENSE 20mV/DIV
500ns/DIV
3829 F04
Figure 4. Voltage Waveform Measured After the Sense Resistor Filter. CF = 1000pF RF = 100 ,
To ensure that the application will deliver full load current over the full operating temperature range, choose the minimum value for the Maximum Current Sense Threshold (VSENSE(MAX)) in the Electrical Characteristics table (25mV, 45mV or 68mV, depending on the state of the ILIM pin). Next, determine the DCR of the inductor. Where provided, use the manufacturer's maximum value, usually given at 20C. Increase this value to account for the temperature coefficient of resistance, which is approximately 0.4%/C.
3829f
LTC3829 applicaTions inForMaTion
A conservative value for TL(MAX) is 100C. To scale the maximum inductor DCR to the desired sense resistor value, use the divider ratio: RD = RSENSE(EQUIV ) DCR(MAX ) at TL(MAX ) less than 40%. For a DCR sensing application, the actual ripple voltage will be determined by the equation: VSENSE = VIN - VOUT VOUT R1* C1 VIN * fOSC
C1 is usually selected to be in the range of 0.047F to 0.47F This forces R1|| R2 to around 2k, reducing error . that might have been caused by the SENSE+ pins' 1A current. TL(MAX) is the maximum inductor temperature. The equivalent resistance R1|| R2 is scaled to the room temperature inductance and maximum DCR: R1|| R2 = L (DCR at 20C ) * C1
Inductor DCR Sensing Temperature Compensation and the ITEMP Pin Inductor DCR current sensing provides a lossless method of sensing the instantaneous current. Therefore, it can provide higher efficiency for applications of high output currents. However, the DCR of the inductor, which is the small amount of DC winding resistance of the copper, typically has a positive temperature coefficient. As the temperature of the inductor rises, its DCR value increases. The current limit of the controller is therefore reduced. The LTC3829 offers a method to counter this inaccuracy by allowing the user to place an NTC temperature sensing resistor near the inductor to actively correct this error. The ITEMP pin, when left floating, is at a voltage around 5V and DCR temperature compensation is disabled. The ITEMP pin has a constant 10A precision current flowing out the pin. By connecting an NTC resistor from the ITEMP pin to SGND, the maximum current sense threshold can be varied over temperature according the following equation: VSENSEMAX( ADJ) = VSENSE(MAX ) * where: VSENSEMAX(ADJ) is the maximum adjusted current sense threshold. VSENSE(MAX) is the maximum current sense threshold specified in the Electrical Characteristics table. It is typically 75mV, 50mV or 30mV depending on the setting ILIM pins. VITEMP is the voltage of the ITEMP pin. The valid voltage range for DCR temperature compensation on the ITEMP pin is between 0.5V to 0.2V, with 0.5V or above being no DCR temperature correction and 0.2V the maximum correction. However, if the duty cycle of the controller is less than 25%, the ITEMP range is extended from 0.5V to 0V.
3829f
The sense resistor values are: R1 = R1|| R2 R1 * RD ; R2 = RD 1 - RD
The LTC3829 also features a DCR temperature compensation circuit by using a NTC temperature sensor. See the Inductor DCR Sensing Temperature Compensation section for details. The maximum power loss in R1 is related to duty cycle, and will occur in continuous mode at the maximum input voltage: PLOSS
1.8 - VITEMP 1.3
(V R1=
IN(MAX ) - VOUT
R1
)* V
OUT
Ensure that R1 has a power rating higher than this value. If high efficiency is necessary at light loads, consider this power loss when deciding whether to use DCR sensing or sense resistors. Light load power loss can be modestly higher with a DCR network than with a sense resistor, due to the extra switching losses incurred through R1. However, DCR sensing eliminates a sense resistor, reduces conduction losses and provides higher efficiency at heavy loads. Peak efficiency is about the same with either method. To maintain a good signal-to-noise ratio for the current sense signal, use a minimum VSENSE of 10mV for duty cycles
LTC3829 applicaTions inForMaTion
The NTC resistor has a negative temperature coefficient, meaning its value decreases as temperature rises. The VITEMP voltage, therefore, decreases as temperature increases and in turn, the VSENSEMAX(ADJ) will increase to compensate the DCR temperature coefficient. The NTC resistor, however, is nonlinear and the user can linearize its value by building a resistor network with regular resistors. Consult the NTC manufacture data sheets for detailed information. Another use for the ITEMP pins, in addition to NTC compensated DCR sensing, is adjusting VSENSE(MAX) to values between the nominal values of 30mV, 50mV and 75mV for a more precise current limit. This is done by applying a voltage less than 0.5V to the ITEMP pin. VSENSE(MAX) will be varied per the previous equation and the same duty cycle limitations will apply. The current limit can be adjusted using this method either with a sense resistor or DCR sensing. NTC Compensated DCR Sensing For DCR sensing applications where a more accurate current limit is required, a network consisting of an NTC thermistor placed from the ITEMP pin to ground will provide correction of the current limit over temperature. Figure 2b shows this network. Resistors RS and RP will linearize the impedance the ITEMP pin sees. To implement NTC compensated DCR sensing, design the DCR sense filter network per the same procedure mentioned in the previous selection, except calculate the divider components using the room temperature value of the DCR. For a single output rail operating from one phase: 1. Set the ITEMP pin resistance to 50k at 25C. With 10A flowing out of the ITEMP pin, the voltage on the ITEMP pin will be 0.5V at room temperature. Current limit correction will occur for inductor temperatures greater than 25C. 2. Calculate the ITEMP pin resistance and the maximum inductor temperature which is typically 100C. Use the equations: RITEMP100C VITEMP100C 10A Calculate the values for RP and RS. A simple method is to graph the following RS versus RP equations with RS on the y-axis and RP on the x-axis. RS = RITEMP25C - RNTC25C || RP RS = RITEMP100C - RNTC100C || RP Next, find the value of RP that satisfies both equations which will be the point where the curves intersect. Once RP is known, solve for RS. The resistance of the NTC thermistor can be obtained from the vendor's data sheet either in the form of graphs, tabulated data or formulas. The approximate value for the NTC thermistor for a given temperature can be calculated from the following equation: 1 1 R = RO * exp B * - T + 273 TO + 273 where: R = resistance at temperature T, which is in degrees C RO = resistance at temperature TO, typically 25C B = B-constant of the thermistor. Figure 5 shows a typical resistance curve for a 100k thermistor and the ITEMP pin network over temperature. Starting values for the NTC compensation network are listed below: * NTC RO = 100k * RS = 20k * RP = 50k But, the final values should be calculated using the above equations and checked at 25C and 100C.
VITEMP100C = 0.5V - 1.3
IMAX * DCR(MAX) * R2 / (R1+ R2) * (100C - 25C) * 0.4 / 100 VSENSE(MAX )
3829f
LTC3829 applicaTions inForMaTion
10000 THERMISTOR RESISTANCE RO = 100k TO = 25C B = 4334 FOR 25C/100C 1000 RESISTANCE (k )
100 RITMP RS = 20k RP = 43.2k 100k NTC
Generating the IMAX versus inductor temperature curve plot first using the above values as a starting point and then adjusting the RS and RP values as necessary is another approach. Figure 6 shows a typical curve of IMAX versus inductor temperature. The same thermistor network can be used to correct for temperatures less than 25C. But make sure VITEMP is greater than 0.2V for duty cycles of 25% or more, otherwise temperature correction may not occur at elevated ambients. For the most accurate temperature detection, place the thermistors next to the inductors as shown in Figure 7. Take care to keep the ITEMP pin away from the switch nodes.
25
10
1 -40 -20 0 20 40 60 80 100 120 INDUCTOR TEMPERATURE (C)
3829 F05
Figure 5. Resistance Versus Temperature for the ITEMP Pin Network and the 100k NTC
After determining the components for the temperature compensation network, check the results by plotting IMAX versus inductor temperature using the following equations:
IMAX (A)
20 15 NOMINAL IMAX 10
CORRECTED IMAX
IMAX =
VSENSEMAX( ADJ) - VSENSE / 3
DCR(MAX) at 25C * 1+ TL(MAX ) - 25C * 0.4 / 100 +
((
)
)
where:
VSENSEMAX( ADJ) = VSENSE(MAX ) * 1.8 V - VITEMP -A 1.3
VITEMP = 10A * (RS + RP || RNTC )
UNCORRECTED RS = 20k IMAX RP = 43.2k NTC THERMISTOR: 5 R = 100k O TO = 25C B = 4334 0 -40 -20 0 20 40 60 80 100 120 INDUCTOR TEMPERATURE (C)
3829 F06
Use typical values for VSENSE(MAX). Subtracting constant A will provide a minimum value for VSENSE(MAX). These values are summarized in Table 1.
Table 1
ILIM VSENSE(MAX) TYP A GND 30mV 5mV FLOAT 50mV 5mV INTVCC 75mV 7mV
Figure 6. Worst-Case IMAX Versus Inductor Temperature Curve with and without NTC Temperature Compensation
VOUT
RNTC
L1
L2
L3
The resulting current limit should be greater than or equal to IMAX for inductor temperatures between 25C and 100C. These are typical values for the NTC compensation network: * NTC RO = 100k, B-constant = 3000 to 4000 * RS 20k * RP 50k
SW1
SW2
SW3
3829 F07
Figure 7. Thermistor Location. Place Thermistor Next to Inductor(s) for Accurate Sensing of the Inductor Temperature, But Keep the ITEMP Pin Away from the Switch Nodes and Gate Drive Traces
3829f
0
LTC3829 applicaTions inForMaTion
Slope Compensation and Inductor Peak Current Slope compensation provides stability in constant frequency current mode architectures by preventing sub-harmonic oscillation at high duty cycles. It is accomplished internally by adding a compensating ramp to the inductor current signal at duty cycles in excess of 40%. Normally, this results in a reduction of maximum inductor peak current for duty cycles greater than 40%. However, the LTC3829 uses a scheme that counteracts this compensating ramp, which allows the maximum inductor peak current to remain unaffected throughout all duty cycles. Inductor Value Calculation and Output Ripple Current The operating frequency and inductor selection are interrelated in that higher operating frequencies allow the use of smaller inductor and capacitor values. A higher frequency generally results in lower efficiency because of MOSFET gate charge and transition losses. In addition to this basic trade-off, the effect of inductor value on ripple current and low current operation must also be considered. The PolyPhase approach reduces both input and output ripple currents while optimizing individual output stages to run at a lower fundamental frequency, enhancing efficiency. The inductor value has a direct effect on ripple current. The inductor ripple current, IL, per individual section
1.0 0.9 0.8 0.7 DIO(P-P) VO/fL 0.6 0.5 0.4 0.3 0.2 0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 DUTY FACTOR (VOUT/VIN) 0.8 0.9 1-PHASE 2-PHASE 3-PHASE 4-PHASE 6-PHASE 12-PHASE
N, decreases with higher inductance or frequency and increases with higher VIN or VOUT : IL = VOUT VOUT 1- f *L VIN
where f is the individual output stage operating frequency. In a PolyPhase converter, the net ripple current seen by the output capacitor is much smaller than the individual inductor ripple currents due to the ripple cancellation. The details on how to calculate the net output ripple current can be found in Application Note 77. Figure 8 shows the net ripple current seen by the output capacitors for the different phase configurations. The output ripple current is plotted for a fixed output voltage as the duty factor is varied between 10% and 90% on the x-axis. The output ripple current is normalized against the inductor ripple current at zero duty factor. The graph can be used in place of tedious calculations. The zero output ripple current is obtained when: VOUT k = where k = 1, 2,...,N - 1 VIN N
3829 F08
Figure 8. Normalized Peak Output Current vs Duty Factor [IRMS = 0.3(IOP-P)]
3829f
LTC3829 applicaTions inForMaTion
Power MOSFET and Schottky Diode (Optional) Selection At least two external power MOSFETs must be selected for each of the three output sections: One N-channel MOSFET for the top (main) switch and one or more N-channel MOSFET(s) for the bottom (synchronous) switch. The number, type and on-resistance of all MOSFETs selected take into account the voltage step-down ratio as well as the actual position (main or synchronous) in which the MOSFET will be used. A much smaller and much lower input capacitance MOSFET should be used for the top MOSFET in applications that have an output voltage that is less than 1/3 of the input voltage. In applications where VIN >> VOUT , the top MOSFETs' on-resistance is normally less important for overall efficiency than its input capacitance at operating frequencies above 300kHz. MOSFET manufacturers have designed special purpose devices that provide reasonably low on-resistance with significantly reduced input capacitance for the main switch application in switching regulators. The peak-to-peak MOSFET gate drive levels are set by the voltage, VCC, requiring the use of logic-level threshold MOSFETs in most applications. Pay close attention to the BVDSS specification for the MOSFETs as well; many of the logic-level MOSFETs are limited to 30V or less. Selection criteria for the power MOSFETs include the on-resistance, RDS(ON), input capacitance, input voltage and maximum output current. MOSFET input capacitance is a combination of several components but can be taken from the typical gate charge curve included on most data sheets (Figure 9). The curve is generated by forcing a constant input current into the gate of a common source, current source loaded stage and then plotting the gate voltage versus time.
VIN VGS MILLER EFFECT a QIN CMILLER = (QB - QA)/VDS b VGS V
The initial slope is the effect of the gate-to-source and the gate-to-drain capacitance. The flat portion of the curve is the result of the Miller multiplication effect of the drain-to-gate capacitance as the drain drops the voltage across the current source load. The upper sloping line is due to the drain-to-gate accumulation capacitance and the gate-to-source capacitance. The Miller charge (the increase in coulombs on the horizontal axis from a to b while the curve is flat) is specified for a given VDS drain voltage, but can be adjusted for different VDS voltages by multiplying the ratio of the application VDS to the curve specified VDS values. A way to estimate the CMILLER term is to take the change in gate charge from points a and b on a manufacturer's data sheet and divide by the stated VDS voltage specified. CMILLER is the most important selection criteria for determining the transition loss term in the top MOSFET but is not directly specified on MOSFET data sheets. CRSS and COS are specified sometimes but definitions of these parameters are not included. When the controller is operating in continuous mode the duty cycles for the top and bottom MOSFETs are given by: Main Switch Duty Cycle = VOUT VIN
V -V Synchronous Switch Duty Cycle = IN OUT VIN The power dissipation for the main and synchronous MOSFETs at maximum output current are given by: V I PMAIN = OUT MAX VIN N
2
(1+ )RDS(ON) +
( VIN )2 IMAX (RDR )(CMILLER ) * 2
1 1 + *f VCC - VTH(IL ) VTH(IL) PSYNC = VIN - VOUT IMAX N VIN
2
+
-
+V DS -
3729 F09
(1+ )RDS(ON)
Figure 9. Gate Charge Characteristic
3829f
LTC3829 applicaTions inForMaTion
where N is the number of output stages, is the temperature dependency of RDS(ON), RDR is the effective top driver resistance (approximately 2 at VGS = VMILLER), VIN is the drain potential and the change in drain potential in the particular application. VTH(IL) is the data sheet specified typical gate threshold voltage specified in the power MOSFET data sheet at the specified drain current. CMILLER is the calculated capacitance using the gate charge curve from the MOSFET data sheet and the technique described above. Both MOSFETs have I2R losses while the topside N-channel equation includes an additional term for transition losses, which peak at the highest input voltage. For VIN < 20V, the high current efficiency generally improves with larger MOSFETs, while for VIN > 20V, the transition losses rapidly increase to the point that the use of a higher RDS(ON) device with lower CMILLER actually provides higher efficiency. The synchronous MOSFET losses are greatest at high input voltage when the top switch duty factor is low or during a short-circuit when the synchronous switch is on close to 100% of the period. The term (1 + ) is generally given for a MOSFET in the form of a normalized RDS(ON) vs temperature curve, but = 0.005/C can be used as an approximation for low voltage MOSFETs. The optional Schottky diodes conduct during the dead time between the conduction of the two large power MOSFETs. This prevents the body diode of the bottom MOSFET from turning on, storing charge during the dead time and requiring a reverse-recovery period which could cost as much as several percent in efficiency. A 2A to 8A Schottky is generally a good compromise for both regions of operation due to the relatively small average current. Larger diodes result in additional transition loss due to their larger junction capacitance. CIN and COUT Selection In continuous mode, the source current of each top N-channel MOSFET is a square wave of duty cycle VOUT/ VIN. A low ESR input capacitor sized for the maximum RMS current must be used. The details of a close form equation can be found in Application Note 77. Figure 10 shows the input capacitor ripple current for different phase configurations with the output voltage fixed and input voltage varied. The input ripple current is normalized against the DC output current. The graph can be used in place of tedious calculations. The minimum input ripple current can be achieved when the product of phase number and output voltage, N(VOUT), is approximately equal to the input voltage VIN or: VOUT k = where k = 1, 2,...,N - 1 VIN N So the phase number can be chosen to minimize the input capacitor size for the given input and output voltages. In the graph of Figure 10, the local maximum input RMS capacitor currents are reached when: VOUT 2k - 1 where k = 1, 2,...,N = VIN N These worst-case conditions are commonly used for design because even significant deviations do not offer much relief. Note that capacitor manufacturer's ripple current ratings are often based on only 2000 hours of life. This makes it advisable to further derate the capacitor or to choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. Always consult the capacitor manufacturer if there is any question.
3829f
LTC3829 applicaTions inForMaTion
The Figure 10 graph shows that the peak RMS input current is reduced linearly, inversely proportional to the number N of stages used. It is important to note that the efficiency loss is proportional to the input RMS current squared and therefore a 3-stage implementation results in 90% less power loss when compared to a single-phase design. Battery/input protection fuse resistance (if used), PC board trace and connector resistance losses are also reduced by the reduction of the input ripple current in a PolyPhase system. The required amount of input capacitance is further reduced by the factor N, due to the effective increase in the frequency of the current pulses. Ceramic capacitors are becoming very popular for small designs but several cautions should be observed. X7R, X5R and Y5V are examples of a few of the ceramic materials used as the dielectric layer, and these different dielectrics have very different effect on the capacitance value due to the voltage and temperature conditions applied. Physically, if the capacitance value changes due to applied voltage change, there is a concommitant piezo effect which results in radiating sound! A load that draws varying current at an audible rate may cause an attendant varying input voltage on a ceramic capacitor, resulting in an audible signal. A secondary issue relates to the energy flowing back into a ceramic capacitor whose capacitance value is being reduced by the increasing charge. The voltage can increase
0.6 0.5 0.4 0.3 0.2 0.1 0 1-PHASE 2-PHASE 3-PHASE 4-PHASE 6-PHASE 12-PHASE
at a considerably higher rate than the constant current being supplied because the capacitance value is decreasing as the voltage is increasing! Nevertheless, ceramic capacitors, when properly selected and used, can provide the lowest overall loss due to their extremely low ESR. The selection of COUT is driven by the required effective series resistance (ESR). Typically once the ESR requirement is satisfied the capacitance is adequate for filtering. The steady-state output ripple (VOUT) is determined by: 1 VOUT IRIPPLE ESR + 8NfCOUT where f = operating frequency of each stage, N is the number of output stages, COUT = output capacitance and IL = ripple current in each inductor. The output ripple is highest at maximum input voltage since IL increases with input voltage. The output ripple will be less than 50mV at maximum VIN with IL = 0.4IOUT(MAX) assuming: COUT required ESR < N * RSENSE and COUT > 1 (8Nf)(RSENSE )
RMS INPUT RIPPLE CURRENT DC LOAD CURRENT
0.1
0.2
0.3 0.4 0.5 0.6 0.7 DUTY FACTOR (VOUT/VIN)
0.8
0.9
3829 F10
Figure 10. Normalized Input RMS Ripple Current vs Duty Factor for One to Six Output Stages
3829f
LTC3829 applicaTions inForMaTion
The emergence of very low ESR capacitors in small, surface mount packages makes very small physical implementations possible. The ability to externally compensate the switching regulator loop using the ITH pin allows a much wider selection of output capacitor types. The impedance characteristic of each capacitor type is significantly different than an ideal capacitor and therefore requires accurate modeling or bench evaluation during design. Manufacturers such as Nichicon, Nippon Chemi-Con and Sanyo should be considered for high performance through-hole capacitors. The OS-CON semiconductor dielectric capacitors available from Sanyo and the Panasonic SP surface mount types have a good (ESR)(size) product. Once the ESR requirement for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. Ceramic capacitors from AVX, Taiyo Yuden, Murata and Tokin offer high capacitance value and very low ESR, especially applicable for low output voltage applications. In surface mount applications, multiple capacitors may have to be paralleled to meet the ESR or RMS current handling requirements of the application. Aluminum electrolytic and dry tantalum capacitors are both available in surface mount configurations. New special polymer surface mount capacitors offer very low ESR also but have much lower capacitive density per unit volume. In the case of tantalum, it is critical that the capacitors are surge tested for use in switching power supplies. Several excellent choices are the AVX TPS, AVX TPSV, the KEMET T510 series of surface mount tantalums or the Panasonic SP series of surface mount special polymer capacitors available in case heights ranging from 2mm to 4mm. Other capacitor types include Sanyo POSCAP Sanyo OS-CON, , Nichicon PL series and Sprague 595D series. Consult the manufacturers for other specific recommendations. Differential Amplifier The LTC3829 has a true remote voltage sense capability. The sensing connections should be returned from the load, back to the differential amplifier's inputs through a common, tightly coupled pair of PC traces. The differential amplifier rejects common mode signals capacitively or inductively radiated into the feedback PC traces as well as ground loop disturbances. The differential amplifier output signal is divided by a pair of resistors and is compared with the internal, precision 0.6V voltage reference by the error amplifier. Active Voltage Positioning (AVP) In an application, the AVP scheme modifies the regulated output voltage depending its current loading. AVP can improve overall transient response and save power consumption. The LTC3829 senses inductor current information through monitoring voltage drops on the sense resistor RSENSE or DCR sensing network of all three channels. The voltage drops are added together and applied as VPRE-AVP between the AVP and DIFFP pins, which are connected through resistor RPRE-AVP . Then VPRE-AVP is scaled through RAVP and added to output voltage as the compensation for the load voltage drop. Let: V = VSENSE1+ - VSENSE1- V = VSENSE2+ - VSENSE2- V = VSENSE3+ - VSENSE3- then: R AVP VDIFFP,VOUT = 3 * V RPRE-AVP
3829f
LTC3829 applicaTions inForMaTion
The final load slope is defined by the inductor current sense resistors and the two external resistors mentioned above. In summary, the load slope is: R AVP RSENSE * V/ A RPRE-AVP The recommended value for RAVP is 90 to 100. The maximum output voltage at AVP is 2.5V. Therefore, for output higher than 2.5V, AVP function is not supported. The DIFFP pin, however, should always be connected to the output even when AVP or diffamp functions are not used. Programmable Shed Mode When the MODE pin is tied to INTVCC, the LTC3829 enters shed mode. It means that the second and third channel will stop switching when ITH is below a certain programmed threshold. The threshold voltage on ITH when LTC3829 goes into shed mode, is programmed according to the following formula: VSHED = 0.5 + (5/3) * (0.5 - VISET) The valid range of VISET is between 0V to 0.5V and VISET is the voltage on the ISET pin. There is a precision 7.5A flowing out of the ISET pin. Connecting a resistor to SGND sets the VISET voltage. When left floating, VISET voltage will be at INTVCC. The shed mode threshold voltage in this case will be 0.5V. There is a 50mV hysteresis for the shed mode threshold comparator. Programmable Burst Mode Operation When the MODE pin is floating, the LTC3829 enters Burst Mode operation. This means that all channels will stop switching when ITH is below a certain threshold. The Burst Mode clamp, which sets the current limit when bursting, can be programmed through VISET according to the following equation: VCLAMP = 0.7 + 0.62 (0.5 - VISET) The valid range of VISET is between 0.3V to 0.5V and VISET is the voltage on the ISET pin. There is a precision 7.5A flowing out of ISET. Connecting a resistor to SGND sets the VISET voltage. When left floating, the VISET voltage will be at INTVCC. The Burst Mode clamp voltage in this case will be 0.7V. There is a 50mV hysteresis for the Burst Mode comparator. Nonlinear Control Loop The LTC3829 features a unique control loop that can speed up transient response dramatically. This feature is enabled and programmed through the IFAST pin. When IFAST is tied to INTVCC, the nonlinear control loop is disabled. VIFAST is the voltage that can be programmed on the IFAST pin. There is a precision 10A flowing out of the ISET pin. Connecting a resistor to SGND sets the VIFAST voltage. When VIFAST is set below 0.5V, the difference of 0.5V and VIFAST sets the threshold voltage that triggers nonlinear control.
3829f
LTC3829 applicaTions inForMaTion
Nonlinear control is only enabled when VFB is within the UV and OV window. It should be enabled only for forced continuous mode of operation. Once nonlinear control is enabled, the top gate of all channels will turn on if: VFB = VREF - 0.5 - VIFAST * 1.2 5 0.5 - VIFAST 5 disabled during this phase to ensure smooth soft-start or tracking. The soft-start or tracking range is defined to be the voltage range from 0V to 0.6V on the TK/SS pin. The total soft-start time can be calculated as: t SOFTSTART = 0.6 * CSS 1.25A
The top gate of all channels will turn off if: VFB = VREF +
where VREF is the reference voltage, normally at 0.6V, and VFB is the feedback voltage. Soft-Start and Tracking The LTC3829 has the ability to either soft-start by itself with a capacitor or track the output of another channel or external supply. When the controller is configured to softstart by itself, a capacitor should be connected to its TK/SS pin. The controller is in the shutdown state if its RUN pin voltage is below 1.22V and its TK/SS pin is actively pulled to ground in this shutdown state. If the RUN pin voltage is above 1.22V, the controller powers up. A soft-start current of 1.25A then starts to charge the TK/SS soft-start capacitor. Note that soft-start or tracking is achieved not by limiting the maximum output current of the controller but by controlling the output ramp voltage according to the ramp rate on the TK/SS pin. Current foldback is
Regardless of the mode selected by the MODE pin, the controller always starts in discontinuous mode up to TK/SS = 0.5V. Between TK/SS = 0.5V and 0.54V, it will operate in forced continuous mode and revert to the selected mode once TK/SS > 0.54V. The output ripple is minimized during the 40mV forced continuous mode window ensuring a clean PGOOD signal. When the channel is configured to track another supply, the feedback voltage of the other supply is duplicated by a resistor divider and applied to the TK/SS pin. Therefore, the voltage ramp rate on this pin is determined by the ramp rate of the other supply's voltage. Note that the small soft-start capacitor charging current is always flowing, producing a small offset error. To minimize this error, select the tracking resistive divider value to be small enough to make this error negligible. In order to track down another channel or supply after the soft-start phase expires, the LTC3829 is forced into continuous mode of operation as soon as VFB is below the undervoltage threshold of 0.54V regardless of the setting on the MODE pin. However, the LTC3829 should always be set in forced continuous mode tracking down when there is no load. After TK/SS drops below 0.1V, the controller operates in discontinuous mode.
3829f
LTC3829 applicaTions inForMaTion
The LTC3829 allows the user to program how its output ramps up and down by means of the TK/SS pins. Through these pins, the output can be set up to either coincidentally or ratiometrically track another supply's output, as shown in Figure 11. In the following discussions, VOUT1 refers to the LTC3829's output as a master and VOUT2 refers to another supply output as a slave. To implement the coincident tracking in Figure 11a, connect an additional resistive divider to VOUT1 and connect its mid-point to the TK/SS pin of the slave controller. The ratio of this divider should be the same as that of the slave controller's feedback divider shown in Figure 12a. In this tracking mode, VOUT1 must be set higher than VOUT2. To implement the ratiometric tracking in Figure 11b, the ratio of the VOUT2 divider should be exactly the same as the master controller's feedback divider shown in Figure 12b . By selecting different resistors, the LTC3829 can achieve different modes of tracking including the two in Figure 11. So which mode should be programmed? While either mode in Figure 11 satisfies most practical applications, some trade-offs exist. The ratiometric mode saves a pair of resistors, but the coincident mode offers better output regulation. Under ratiometric tracking, when the master controller's output experiences dynamic excursion (under load transient, for example), the slave controller output will be affected as well. For better output regulation, use the coincident tracking mode instead of ratiometric.
VOUT1 OUTPUT VOLTAGE OUTPUT VOLTAGE
VOUT1
VOUT2
VOUT2
TIME
3829 F11a
TIME
3829 F11b
(11a) Coincident Tracking
(11b) Ratiometric Tracking
Figure 11. Two Different Modes of Output Voltage Tracking
VOUT1 TO TK/SS2 PIN R3 R1 TO VFB1 PIN TO VFB2 PIN R3
VOUT2
VOUT1 TO TK/SS2 PIN R1 TO VFB1 PIN TO VFB2 PIN R3
VOUT2
R4
R2
R4
R2
R4
3829 F12
(12a) Coincident Tracking Setup
(12b) Ratiometric Tracking Setup
Figure 12. Setup and Coincident and Ratiometric Tracking
3829f
LTC3829 applicaTions inForMaTion
INTVCC (LDO) and EXTVCC The LTC3829 features a true PMOS LDO that supplies power to INTVCC from the VIN supply. INTVCC powers the gate drivers and much of the LTC3829's internal circuitry. The LDO regulates the voltage at the INTVCC pin to 5V when VIN is greater than 5.5V. EXTVCC connects to INTVCC through a P-channel MOSFET and can supply the needed power when its voltage is higher than 4.7V. Each of these can supply a peak current of 100mA and must be bypassed to ground with a minimum of 4.7F ceramic capacitor or low ESR electrolytic capacitor. No matter what type of bulk capacitor is used, an additional 0.1F ceramic capacitor placed directly adjacent to the INTVCC and PGND pins is highly recommended. Good bypassing is needed to supply the high transient currents required by the MOSFET gate drivers and to prevent interaction between the channels. High input voltage applications in which large MOSFETs are being driven at high frequencies may cause the maximum junction temperature rating for the LTC3829 to be exceeded. The INTVCC current, which is dominated by the gate charge current, may be supplied by either the 5V LDO or EXTVCC. When the voltage on the EXTVCC pin is less than 4.7V, the LDO is enabled. Power dissipation for the IC in this case is highest and is equal to VIN * IINTVCC. The gate charge current is dependent on operating frequency as discussed in the Efficiency Considerations section. The junction temperature can be estimated by using the equations given in Note 3 of the Electrical Characteristics tables. For example, the LTC3829 INTVCC current is limited to less than 42mA from a 38V supply in the UHF package and not using the EXTVCC supply: TJ = 70C + (42mA)(38V)(34C/W) = 125C To prevent the maximum junction temperature from being exceeded, the input supply current must be checked while operating in continuous conduction mode (MODE = SGND) at maximum VIN. When the voltage applied to EXTVCC rises above 4.7V, the INTVCC LDO is turned off and the EXTVCC is connected to the INTVCC. The EXTVCC remains on as long as the voltage applied to EXTVCC remains above 4.5V. Using the EXTVCC allows the MOSFET driver and control power to be derived from one of switching regulator outputs during normal operation and from the INTVCC when the output is out of regulation (e.g., startup, short circuit). If more current is required through the EXTVCC than is specified, an external Schottky diode can be added between the EXTVCC and INTVCC pins. Do not apply more than 6V to the EXTVCC pin and make sure that EXTVCC < VIN. Significant efficiency and thermal gains can be realized by powering INTVCC from the output, since the VIN current resulting from the driver and control currents will be scaled by a factor of (duty cycle)/(switcher efficiency). Tying the EXTVCC pin to a 5V supply reduces the junction temperature in the previous example from 125C to: TJ = 70C + (42mA)(5V)(34C/W) = 77C However, for low voltage outputs, additional circuitry is required to derive INTVCC power from the output. The following list summarizes the four possible connections for EXTVCC: 1. EXTVCC left open (or grounded). This will cause INTVCC to be powered from the internal 5V LDO resulting in an efficiency penalty of up to 10% at high input voltages. 2. EXTVCC connected directly to VOUT . This is the normal connection for a 5V regulator and provides the highest efficiency. 3. EXTVCC connected to an external supply. If a 5V external supply is available, it may be used to power EXTVCC providing it is compatible with the MOSFET gate drive requirements.
3829f
LTC3829 applicaTions inForMaTion
4. EXTVCC connected to an output-derived boost network. For 3.3V and other low voltage regulators, efficiency gains can still be realized by connecting EXTVCC to an output-derived voltage that has been boosted to greater than 4.7V. For applications where the main input power is 5V, tie the VIN and INTVCC pins together and tie the combined pins to the 5V input with a 1 or 2.2 resistor as shown in Figure 13 to minimize the voltage drop caused by the gate charge current. This will override the INTVCC linear regulator and will prevent INTVCC from dropping too low due to the dropout voltage. Make sure the INTVCC voltage is at or exceeds the RDS(ON) test voltage for the MOSFET which is typically 4.5V for logic-level devices Topside MOSFET Driver Supply (CB, DB) External bootstrap capacitors, CB, connected to the BOOST pins supply the gate drive voltages for the topside MOSFETs. Capacitor CB in the Functional Diagram is charged though external diode DB from INTVCC when the SW pin is low. When one of the topside MOSFETs is to be turned on, the driver places the CB voltage across the gate source of the desired MOSFET. This enhances the MOSFET and turns on the topside switch. The switch node voltage, SW, rises to VIN and the BOOST pin follows. With the topside MOSFET on, the boost voltage is above the input supply: VBOOST = VIN + VINTVCC
VOUT LTC3829 VIN INTVCC RVIN 1 CINTVCC 4.7F LTC3829 RB CFF
The value of the boost capacitor, CB, needs to be 100 times that of the total input capacitance of the topside MOSFET(s). The reverse breakdown of the external Schottky diode must be greater than VIN(MAX). When adjusting the gate drive level, the final arbiter is the total input current for the regulator. If a change is made and the input current decreases, then the efficiency has improved. If there is no change in input current, then there is no change in efficiency. Setting Output Voltage The LTC3829 output voltage is set by an external feedback resistive divider carefully placed across the output, as shown in Figure 14. The regulated output voltage is determined by: R VOUT = 0.6 V * 1+ B RA To improve the frequency response, a feedforward capacitor, CFF , may be used. Great care should be taken to route the VFB line away from noise sources, such as the inductor or the SW line. If diffamp is used, then the resistor, RB, should connect to the output of the diffamp, DIFFOUT.
+
5V CIN
3829 F13
VFB RA
3829 F14
Figure 13. Setup for a 5V Input
Figure 14. Setting Output Voltage
3829f
0
LTC3829 applicaTions inForMaTion
Fault Conditions: Current Limit and Current Foldback The LTC3829 includes current foldback to help limit load current when the output is shorted to ground. If the output falls below 50% of its nominal output level, then the maximum sense voltage is progressively lowered from its maximum programmed value to one-third of the maximum value. Foldback current limiting is disabled during the soft-start or tracking up. Under short-circuit conditions with very low duty cycles, the LTC3829 will begin cycle skipping in order to limit the short-circuit current. In this situation the bottom MOSFET will be dissipating most of the power but less than in normal operation. The short circuit ripple current is determined by the minimum ontime tON(MIN) of the LTC3829 (90ns), the input voltage and inductor value: IL(SC) = tON(MIN) * VIN L The output of the phase detector is a pair of complementary current sources that charge or discharge the internal filter network. There is a precision 10A of current flowing out of FREQ pin. This allows the user to use a single resistor to SGND to set the switching frequency when no external clock is applied to the PLLIN pin. The internal switch between the FREQ pin and the integrated PLL filter network is on, allowing the filter network to be pre-charged at the same voltage as of the FREQ pin. The relationship between the voltage on the FREQ pin and operating frequency is shown in Figure 15 and specified in the Electrical Characteristics table. If an external clock is detected on the PLLIN pin, the internal switch mentioned above turns off and isolates the influence of the FREQ pin. Note that the LTC3829 can only be synchronized to an external clock whose frequency is within range of the LTC3829's internal VCO. This is guaranteed to be between 250kHz and 770kHz. A simplified block diagram is shown in Figure 16. If the external clock frequency is greater than the internal oscillator's frequency, fOSC, then current is sourced continuously from the phase detector output, pulling up the filter network. When the external clock frequency is less than fOSC, current is sunk continuously, pulling down the filter network. If the external and internal frequencies are the same but exhibit a phase difference, the current sources turn on for an amount of time corresponding to the phase difference. The voltage on the filter network is adjusted until the phase and frequency of the internal and external oscillators are identical. At the stable operating point, the phase detector output is high impedance and the filter capacitor CLP holds the voltage. Typically, the external clock (on the PLLIN pin) input high threshold is 1.6V, while the input low threshold is 1V.
The resulting short-circuit current is: 1/ 3 VSENSE(MAX ) 1 ISC = - IL(SC) * 3 RSENSE 2 Phase-Locked Loop and Frequency Synchronization The LTC3829 has a phase-locked loop (PLL) comprised of an internal voltage-controlled oscillator (VCO) and a phase detector. This allows the turn-on of the top MOSFET of controller 1 to be locked to the rising edge of an external clock signal applied to the PLLIN pin. The turn-on of the second phases' top MOSFETs is thus 120 out of phase with the external clock and so on. The phase detector is an edge sensitive digital type that provides zero degrees phase shift between the external and internal oscillators. This type of phase detector does not exhibit false lock to harmonics of the external clock.
3829f
LTC3829 applicaTions inForMaTion
900 800 700 FREQUENCY (kHz) 600 500 400 300 200 100 0 0 0.5 1 1.5 FREQ PIN VOLTAGE (V) 2 2.5
38501 F15
Figure 15. Relationship Between Oscillator Frequency and Voltage at the FREQ Pin
2.4V
5V 10A RSET FREQ
EXTERNAL OSCILLATOR
PLLIN
DIGITAL SYNC PHASE/ FREQUENCY DETECTOR
VCO
3829 F16
Figure 16. Phase-Locked Loop Block Diagram
Minimum On-Time Considerations Minimum on-time, tON(MIN), is the smallest time duration that the LTC3829 is capable of turning on the top MOSFET. It is determined by internal timing delays and the gate charge required to turn on the top MOSFET. Low duty cycle applications may approach this minimum on-time limit and care should be taken to ensure that: tON(MIN) < VOUT VIN ( f )
If the duty cycle falls below what can be accommodated by the minimum on-time, the controller will begin to skip cycles. The output voltage will continue to be regulated,
but the ripple voltage and current will increase. The minimum on-time for the LTC3829 is approximately 90ns, with reasonably good PCB layout, minimum 30% inductor current ripple and at least 10mV ripple on the current sense signal. The minimum on-time can be affected by PCB switching noise in the voltage and current loop. As the peak sense voltage decreases the minimum on-time gradually increases to 130ns. This is of particular concern in forced continuous applications with low ripple current at light loads. If the duty cycle drops below the minimum on-time limit in this situation, a significant amount of cycle skipping can occur with correspondingly larger current and voltage ripple.
3829f
LTC3829 applicaTions inForMaTion
Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: %Efficiency = 100% - (L1 + L2 + L3 + ...) where L1, L2, etc. are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC3829 circuits: 1) IC VIN current, 2) INTVCC regulator current, 3) I2R losses, 4) topside MOSFET transition losses. 1. The VIN current is the DC supply current given in the Electrical Characteristics table, which excludes MOSFET driver and control currents. VIN current typically results in a small (<0.1%) loss. 2. INTVCC current is the sum of the MOSFET driver and control currents. The MOSFET driver current results from switching the gate capacitance of the power MOSFETs. Each time a MOSFET gate is switched from low to high to low again, a packet of charge dQ moves from INTVCC to ground. The resulting dQ/dt is a current out of INTVCC that is typically much larger than the control circuit current. In continuous mode, IGATECHG = f(QT + QB), where QT and QB are the gate charges of the topside and bottom side MOSFETs. Supplying INTVCC power through EXTVCC from an output-derived source will scale the VIN current required for the driver and control circuits by a factor of (duty cycle)/(efficiency). For example, in a 20V to 5V application, 10mA of INTVCC current results in approximately 2.5mA of VIN current. This reduces the mid-current loss from 10% or more (if the driver was powered directly from VIN) to only a few percent. 3. I2R losses are predicted from the DC resistances of the fuse (if used), MOSFET, inductor and current sense resistor. In continuous mode, the average output current flows through L and RSENSE, but is chopped between the topside MOSFET and the synchronous MOSFET. If the two MOSFETs have approximately the same RDS(ON), then the resistance of one MOSFET can simply be summed with the resistances of L and RSENSE to obtain I2R losses. For example, if each RDS(ON) = 10m, RL = 10m, RSENSE = 5m, then the total resistance is 25m. This results in losses ranging from 2% to 8% as the output current increases from 3A to 15A for a 5V output, or a 3% to 12% loss for a 3.3V output. Efficiency varies as the inverse square of VOUT for the same external components and output power level. The combined effects of increasingly lower output voltages and higher currents required by high performance digital systems is not doubling but quadrupling the importance of loss terms in the switching regulator system! 4. Transition losses apply only to the topside MOSFET(s), and become significant only when operating at high input voltages (typically 15V or greater). Transition losses can be estimated from: Transition Loss = (1.7) VIN2 * IO(MAX) * CRSS * f Other hidden losses such as copper trace and internal battery resistances can account for an additional 5% to 10% efficiency degradation in portable systems. It is very important to include these system level losses during the design phase. The internal battery and fuse resistance losses can be minimized by making sure that CIN has adequate charge storage and very low ESR at the switching frequency. A 25W supply will typically require a minimum of 20F to 40F of capacitance having a maximum of 20m to 50m of ESR. Other losses including Schottky conduction losses during dead time and inductor core losses generally account for less than 2% total additional loss.
3829f
LTC3829 applicaTions inForMaTion
Checking Transient Response The regulator loop response can be checked by looking at the load current transient response. Switching regulators take several cycles to respond to a step in DC (resistive) load current. When a load step occurs, VOUT shifts by an amount equal to ILOAD (ESR), where ESR is the effective series resistance of COUT . ILOAD also begins to charge or discharge COUT generating the feedback error signal that forces the regulator to adapt to the current change and return VOUT to its steady-state value. During this recovery time VOUT can be monitored for excessive overshoot or ringing, which would indicate a stability problem. The availability of the ITH pin not only allows optimization of control loop behavior but also provides a DC-coupled and AC-filtered closed-loop response test point. The DC step, rise time and settling at this test point truly reflects the closed-loop response. Assuming a predominantly second order system, phase margin and/or damping factor can be estimated using the percentage of overshoot seen at this pin. The bandwidth can also be estimated by examining the rise time at the pin. The ITH external components shown in the Typical Application circuit will provide an adequate starting point for most applications. The ITH series RC-CC filter sets the dominant pole-zero loop compensation. The values can be modified slightly (from 0.5 to 2 times their suggested values) to optimize transient response once the final PC layout is done and the particular output capacitor type and value have been determined. The output capacitors need to be selected because the various types and values determine the loop gain and phase. An output current pulse of 20% to 80% of full-load current having a rise time of 1s to 10s will produce output voltage and ITH pin waveforms that will give a sense of the overall loop stability without breaking the feedback loop. Placing a power MOSFET directly across the output capacitor and driving the gate with an appropriate signal generator is a practical way to produce a realistic load step condition. The initial output voltage step resulting from the step change in output current may not be within the bandwidth of the feedback loop, so this signal cannot be used to determine phase margin. This is why it is better to look at the ITH pin signal which is in the feedback loop and is the filtered and compensated control loop response. The gain of the loop will be increased by increasing RC and the bandwidth of the loop will be increased by decreasing CC. If RC is increased by the same factor that CC is decreased, the zero frequency will be kept the same, thereby keeping the phase shift the same in the most critical frequency range of the feedback loop. The output voltage settling behavior is related to the stability of the closed-loop system and will demonstrate the actual overall supply performance. A second, more severe transient is caused by switching in loads with large (>1F) supply bypass capacitors. The discharged bypass capacitors are effectively put in parallel with COUT , causing a rapid drop in VOUT . No regulator can alter its delivery of current quickly enough to prevent this sudden step change in output voltage if the load switch resistance is low and it is driven quickly. If the ratio of CLOAD to COUT is greater than 1:50, the switch rise time should be controlled so that the load rise time is limited to approximately 25 * CLOAD. Thus a 10F capacitor would require a 250s rise time, limiting the charging current to about 200mA. PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the IC. These items are also illustrated graphically in the layout diagram of Figure 17. Check the following in the PC layout:
3829f
LTC3829 applicaTions inForMaTion
1. Keep the SGND at one end of a printed circuit path thus preventing MOSFET currents from traveling under the IC. The INTVCC decoupling capacitor should be placed immediately adjacent to the IC between the INTVCC pin and PGND plane. A 1F ceramic capacitor of the X7R or X5R type is small enough to fit very close to the IC to minimize the ill effects of the large current pulses drawn to drive the bottom MOSFETs. An additional 5F to 10F of ceramic, tantalum or other very low ESR capacitance is recommended in order to keep the internal IC supply quiet. The power ground returns to the sources of the bottom N-channel MOSFETs, anodes of the Schottky diodes and (-) plates of CIN, which should have as short lead lengths as possible. 2. Does the IC DIFFP pin connect to the (+) plates of COUT? A 30pF to 300pF feedforward capacitor between the DIFFP and VFB pins should be placed as close as possible to the IC. 3. Are the SENSE- and SENSE+ printed circuit traces for each channel routed together with minimum PC trace spacing? The filter capacitors between SENSE+ and SENSE- for each channel should be as close as possible to the pins of the IC. Connect the SENSE- and SENSE+ pins to the pads of the sense resistor as illustrated in Figure 1. 4. Do the (+) plates of CPWR connect to the drains of the topside MOSFETs as closely as possible? This capacitor provides the pulsed current to the MOSFETs. 5. Keep the switching nodes, SWn, BOOSTn and TGn away from sensitive small-signal nodes (SENSE+, , SENSE-, DIFFP DIFFN, VFB). Ideally the SWn, BOOSTn and TGn printed circuit traces should be routed away and separated from the IC and especially the quiet side of the IC. Separate the high dv/dt traces from sensitive small-signal nodes with ground traces or ground planes. 6. Use a low impedance source such as a logic gate to drive the PLLIN pin and keep the lead as short as possible. 7. The 47pF to 330pF ceramic capacitor between the ITH pin and signal ground should be placed as close as possible to the IC. Figure 17 illustrates all branch currents in a 3-phase switching regulator. It becomes very clear after studying the current waveforms why it is critical to keep the high switching current paths to a small physical size. High electric and magnetic fields will radiate from these loops just as radio stations transmit signals. The output capacitor ground should return to the negative terminal of the input capacitor and not share a common ground path with any switched current paths. The left half of the circuit gives rise to the noise generated by a switching regulator. The ground terminations of the synchronous MOSFETs and Schottky diodes should return to the bottom plate(s) of the input capacitor(s) with a short isolated PC trace since very high switched currents are present. External OPTI-LOOP(R) compensation allows overcompensation for PC layouts which are not optimized but this is not the recommended design procedure.
3829f
LTC3829 applicaTions inForMaTion
L1 SW1 RSENSE1
D1
VIN SW2 RIN
L2 RSENSE2 COUT
VOUT
+
CIN
D2
+
RL
BOLD LINES INDICATE HIGH, SWITCHING CURRENTS. KEEP LINES TO A MINIMUM LENGTH. SW3 D3
L3 RSENSE3
3829 F17
Figure 17. Branch Current Waveform
3829f
1.5V, 60A Converter Using Sense Resistors, fSW = 400kHz
VIN 100k 0.1F MODE RUN 40.2k INTVCC 4.7F 16V Q1 L1 0.33H RSENSE1 0.001 S1P S1N VOUT 25 24 D1 CMDSH-3 33 32 31 30 D2 CMDSH-3 26 27 28 SW2 BG2 D3 CMDSH-3 19 20 21 22 VIN 10 10F 16V X5R TG3 S2N R23 100 R22 100 R21 100 S2P S1N S1P BG3 SW3 Q9 L3 0.33H S3P S3N VOUT Q11 Q12 RSENSE3 0.001 100F 6.3V X5R VOSENSE- 0.1F Q7 Q8 Q5 L2 0.33H 29 0.1F TG2 S2P S2N 10F 16V X5R BG1 SW1 VIN Q1,Q5,Q9: RJK0305DPB Q3,Q4,Q7,Q8,Q11,Q12: RJK0330DPB 0.1F TG1 Q3 Q4 18 16 10 35 3 ILIM FREQ RUN PLLIN MODE IFAST VIN INTVCC BOOST1 TG1 SW1 BG1 LTC3829 BOOST2 TG2 SW2 BG2 BOOST3 TG3 SW3 BG3 34 13 14 15 ISET DIFFN DIFFP DIFFOUT AVP EXTVCC PGOOD ITEMP GND TK/SS 1 2 38 4 23 17 37 39 9 ITH VFB CLKOUT 36 180F 16V 180F 16V GND 2.2 VIN 10F 16V X5R
VIN
+
+
VIN 7V TO 14V
DIFFOUT
Typical applicaTion
100pF PLLIN
30.1k
20.0k
47pF
1nF
CLKOUT
13.5k
100F 6.3V X5R
+
330F 2.5V SANYO 2
40.2k
VOSENSE+
VOSENSE-
0
66.5
DIFFOUT
EXTVCC
PGOOD
ITEMP
VOSENSE+ VOUT RSENSE2 0.001 10
CSS 0.1F SENSE1+ SENSE2- SENSE3+ SENSE1- SENSE2+ SENSE3-
100F 6.3V X5R
+
VOUT 1.5V 330F 60A 2.5V SANYO 2 GND
5 C21 1000pF R26 100 S3N S3P R24 100 R25 100 C22 1000pF C23 1000pF
6
7
8 11
12
+
330F 2.5V SANYO 2
3829 TA02
LTC3829
3829f
LTC3829 package DescripTion
(Reference LTC DWG # 05-08-1701 Rev C)
0.70 0.05
UHF Package 38-Lead Plastic QFN (5mm x 7mm)
5.50
0.05 4.10 0.05 3.00 REF
5.15 0.05
3.15 0.05
PACKAGE OUTLINE 0.25 0.05 0.50 BSC 5.5 REF 6.10 7.50 0.05 0.05
RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED PIN 1 NOTCH R = 0.30 TYP OR 0.35 45 CHAMFER 37 38 0.40 0.10 1 2
5.00
0.10
0.75
0.05 0.00 - 0.05
3.00 REF
PIN 1 TOP MARK (SEE NOTE 6)
7.00
0.10
5.50 REF
5.15 0.10
3.15 0.10
(UH) QFN REF C 1107
0.200 REF 0.25
0.05
0.50 BSC
R = 0.125 TYP
R = 0.10 TYP
BOTTOM VIEW--EXPOSED PAD
NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE M0-220 VARIATION WHKD 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
3829f
LTC3829 package DescripTion
(Reference LTC DWG # 05-08-1772 Rev A)
FE Package 38-Lead Plastic TSSOP (4.4mm) Exposed Pad Variation AA
4.75 REF
38 6.60 0.10 4.50 REF 2.74 REF
SEE NOTE 4
9.60 - 9.80* (.378 - .386) 4.75 REF (.187)
20
0.315 0.05 1.05 0.10 0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
6.40 2.74 REF (.252) (.108) BSC
1
0.25 REF
19 1.20 (.047) MAX
4.30 - 4.50* (.169 - .177)
0 -8
0.09 - 0.20 (.0035 - .0079)
0.50 - 0.75 (.020 - .030)
0.50 (.0196) BSC
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3. DRAWING NOT TO SCALE
0.17 - 0.27 (.0067 - .0106) TYP
0.05 - 0.15 (.002 - .006)
FE38 (AA) TSSOP 0608 REV A
4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE
3829f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC3829 Typical applicaTion
1.2V/60A Triple Phase Converter with Active Voltage Positioning, fSW = 400kHz +
TG1 SW1 BG1 PGND SENSE1+ SENSE1- TG2 SW2 BG2 0.3H 0.001 VIN 22F 6V TO 14V 35V 3
4.7F
SW3 SW2 SW1 220pF 100k
INTVCC EXTVCC ITEMP BOOST1 BOOST2 BOOST3 RUN ILIM MODE FREQ ITH TK/SS SGND DIFFOUT AVP ISET VFB DIFFN DIFFP PGOOD
VIN
VIN 0.3H 0.001 VOUT 1.2V 60A
LTC3829
10k
0.1F
IFAST SENSE2+ SENSE2- TG3 SW3 BG3 CLKOUT SENSE3+ SENSE3-
VIN 0.3H 0.001
20k 20k
75
+
100
COUT 330F 4V 6
3829 TA03
relaTeD parTs
PART NUMBER LTC3855 LTC3860 LTC3853 LTC3850/LTC3850-1 LTC3850-2 LTC3854 LTC3851/LTC3851-1 DESCRIPTION Dual, Multiphase, Synchronous DC/DC Step-Down Controller with Differential Remote Sense COMMENTS Phase-Lockable Fixed Frequency 250kHz to 770kHz, 4.5V VIN 38V, 0.8V VOUT 12.5V
Dual, Multiphase Step-Down DC/DC Controller with Differential Works with DRMOS and Power Blocks for High Current Remote Sense and Accurate Current Share Applications Triple Output, Multiphase Synchronous Step-Down DC/DC Controller, RSENSE or DCR Current Sensing and Tracking Phase-Lockable Fixed 250kHz to 750kHz Frequency, 4V VIN 24V, VOUT3 Up to 13.5V
Dual 2-Phase, High Efficiency Synchronous Step-Down DC/DC Phase-Lockable Fixed 250kHz to 780kHz Frequency, 4V VIN 30V, 0.8V VOUT 5.25V Controller, RSENSE or DCR Current Sensing and Tracking Small Footprint Wide VIN Range Synchronous Step-Down DC/DC Controller, RSENSE or DCR Current Sensing No RSENSETM Wide VIN Range Synchronous Step-Down DC/DC Controller, RSENSE or DCR Current Sensing and Tracking High Frequency Synchronous Voltage Mode Step-Down DC/DC Controller Fixed 400kHz Operating Frequency, 4.5V VIN 38V, 0.8V VOUT 5.25V, 2mm x 3mm QFN-12 Phase-Lockable Fixed 250kHz to 750kHz Frequency, 4V VIN 38V, 0.8V VOUT 5.25V, MSOP-16E, 3mm x 3mm QFN-16, SSOP-16 Fast Transient Response, tON(MIN) = 30ns, 4V VIN 38V, 0.6V VOUT 0.8VIN, MSOP-16E, 3mm x 3mm QFN-16
LTC3775 LTC3878 LTC3879
No RSENSE Constant On-Time Synchronous Step-Down DC/DC Very Fast Transient Response, tON(MIN) = 43ns, 4V VIN 38V, Controller, No RSENSE Required 0.8V VOUT 0.9VIN, SSOP-16 No RSENSE Constant On-Time Synchronous Step-Down DC/DC Very Fast Transient Response, tON(MIN) = 43ns, 4V VIN 38V, Controller, No RSENSE Required 0.6V VOUT 0.9VIN, MSOP-16E, 3mm x 3mm QFN-16
3829f
0 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT 0410 * PRINTED IN USA
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2010

▲Up To Search▲

Price & Availability of LTC3829EUHF-TRPBF

	To Download LTC3829EUHF-TRPBF Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .