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LTC3672B-1 Monolithic Fixed-Output 400mA Buck Regulator with Dual 150mA LDOs in 2mm x 2mm DFN FEATURES

DESCRIPTION
The LTC(R)3672B-1 is a triple power supply composed of a 400mA synchronous buck regulator and two 150mA lowdropout linear regulators (LDOs), where one of the LDOs can be powered from the buck output to improve efficiency. Constant-frequency 2.25MHz operation is maintained down to very light loads. The input supply range of 2.9V to 5.5V is especially well-suited for single-cell Lithium-Ion and Lithium-Polymer applications, and for powering low voltage ASICs from 3.3V or 5V rails. The LTC3672B-1 regulates 1.8V at the buck output, 1.2V at the LDO1 output, and 2.8V at the LDO2 output. External component count is minimal--all that is needed is a single inductor, an input capacitor, and output capacitors for each of the three outputs. Control loop compensation is internal to the LTC3672B-1. The LTC3672B-1 is available in a 2mm x 2mm x 0.75mm 8-Lead DFN package.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

Triple Output Supply From a Single 2.9V to 5.5V Input Buck DC/DC: Fixed 1.8V Output, Up to 400mA LDO1: Fixed 1.2V Output, Up to 150mA LDO2: Fixed 2.8V Output, Up to 150mA 2.5% Reference Accuracy Constant Frequency 2.25MHz Operation Minimum External Component Count Current Mode Operation for Excellent Line and Load Transient Response Internal Soft-Start for Each Output Single Enable Pin Turns On/Shuts Down All Three Outputs Tiny 2mm x 2mm x 0.75mm DFN Package
APPLICATIONS

DMB Cellphones Handheld Products (PDA, PMP, GPS) Multivoltage Power for Digital Logic, I/O, FPGAs, CPLDs, ASICs, CPUs, and RF Chipsets
TYPICAL APPLICATION
Buck DC/DC Efficiency vs Load
VIN 2.9V TO 5.5V 4.7 H SW BUCKOUT VIN1 ENABLE INPUT ENALL LDO1 1F LDO2
3672b1 TA01
100 95 VOUT1 1.8V 400mA (250mA IF LDO1 FULLY-LOADED) VOUT2 1.2V 150mA VOUT3 2.8V UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS) 90 EFFICIENCY (%) 85 80 75 70 65 60 0 50 100 150 200 250 300 350 400 ILOAD (mA)
3672b1 TA01b
VIN = 2.9V VIN = 3.6V VIN = 5.5V
2.2 F
VIN GND
10 F
LTC3672B-1 1F
3672B1f
1
LTC3672B-1 ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2, 3)
PIN CONFIGURATION
TOP VIEW SW 1 GND 2 ENALL 3 BUCKOUT 4 9 8 VIN 7 LDO2 6 LDO1 5 VIN1
VIN ............................................................... -0.3V to 6V VIN1, BUCKOUT, ENALL, SW, LDO2 ...........-0.3V to the lesser of (VIN + 0.3V) or 6V LDO1 ............. -0.3V to the lesser of (VIN1 + 0.3V) or 6V Junction Temperature ........................................... 125C Operating Temperature Range...................... -40 to 85C Storage Temperature Range....................... -65 to 125C
DC PACKAGE 8-LEAD (2mm 2mm) PLASTIC DFN TJMAX = 125C, JA = 102C/W, JC = 20C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC3672BEDC-1#PBF TAPE AND REEL LTC3672BEDC-1#TRPBF PART MARKING* LCWH PACKAGE DESCRIPTION 8-Lead (2mm x 2mm) Plastic DFN TEMPERATURE RANGE -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. 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 VUVLO IQ,VIN PARAMETER Input Voltage Range VIN Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis VIN Quiescent Current All Outputs Enabled, No Load Shutdown VIN1 Quiescent Current All Outputs Enabled, No Load Shutdown ENALL Pin Logic Low Voltage ENALL Pin Logic High Voltage ENALL Pin Pulldown Resistance Oscillator Frequency Regulated Output Voltage
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V, unless otherwise noted.
CONDITIONS
MIN 2.9
TYP 1.7 12
MAX 5.5 2 100 400 1 5 1 0.4
UNITS V V mV A A A A V V M
VIN Rising (Note 4) VBUCKOUT = 1.9V VENALL = 0V VIN1 = 1.8V
260
IQ,VIN1
2.3 VENALL = 0V

VIL VIH RENALL fOSC VBUCKOUT IMAXP IOUT,BUCK RP,BUCK RN,BUCK
1.2 5.5 1.8 2.25 1.8 800 0.6 0.7 2.7 1.845 1100
Synchronous Buck Regulator MHz V mA mA
3672B1f
1.755 550 400
PMOS Switch Maximum Peak Current (Note 5) Available Output Current PMOS Switch On-Resistance NMOS Switch On-Resistance
2
LTC3672B-1 ELECTRICAL CHARACTERISTICS
SYMBOL RPD,BUCKOUT RPD,SW tSS,BUCK VLDO1 PARAMETER BUCKOUT Pulldown Resistance in Shutdown SW Pulldown Resistance in Shutdown Soft-Start Time Regulated Output Voltage Line Regulation with Respect to VIN with Respect to VIN1 Load Regulation Available Output Current Short-Circuit Output Current VDROP1 tSS,LDO1 RPD,LDO1 LDO Regulator 2 VLDO2 Regulated Output Voltage Line Regulation with Respect to VIN Load Regulation Available Output Current Short-Circuit Output Current VDROP2 tSS,LDO2 RPD,LDO2 Dropout Voltage (Note 6) Soft-Start Time Output Pulldown Resistance in Shutdown ILDO2 = 150mA LDO2 Output, ILDO2 = 1mA ILDO2 = 1mA, VIN = 3V to 5.5V ILDO2 = 1mA to 150mA 150 453 188 0.1 10 250
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V, unless otherwise noted.
CONDITIONS VENALL = 0V VENALL = 0V MIN TYP 10 10 0.2 LDO1 Output, ILDO1 = 1mA ILDO1 = 1mA VIN = 3V to 5.5V, VIN1 = 1.8V VIN = 3.6V, VIN1 = 1.7V to 1.9V ILDO1 = 1mA to 150mA 150 347 ILDO1 = 150mA 484 0.3 10 2.73 2.8 1 0.1 2.87 570
MAX
UNITS k k ms
LDO Regulator 1: VIN1 = 1.8V Unless Otherwise Noted 1.17 1.2 0.05 1 -0.05 1.23 V mV/V mV/V mV/mA mA mA mV ms k V mV/V mV/mA mA mA mV ms k
Dropout Voltage (Note 6) Soft-Start Time Output Pulldown Resistance in Shutdown
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 LTC3672B-1 is guaranteed to meet performance specifications from 0C to 85C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability.
Note 4: Dynamic supply current is higher due to the gate charge delivered to the buck regulator's internal MOSFET switches at the switching frequency. Note 5: The current limit features of this part are intended to protect the IC from short term or intermittent fault conditions. Continuous operation above the specified maximum specified pin current rating may result in device degradation or failure. Note 6: Dropout voltage is the minimum input to output voltage differential needed to maintain regulation at a specified output current. When LDO1 is in dropout, its output voltage will be equal to: VIN1 - VDROP1. When LDO2 is in dropout, its output voltage will be equal to: VIN - VDROP2.
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LTC3672B-1 TYPICAL PERFORMANCE CHARACTERISTICS
VIN Quiescent Current vs VIN Voltage
500 400 300 200 100 0 2.5 SW PIN NOT SWITCHING 130C 90C IVIN1 (A) 25C -45C 5 4 90C IVIN1 (A) 25C 0.5 0 -50 -25 3 2 1 0 2.5 130C
TA = 25C unless otherwise specified. VIN1 Quiescent Current vs Temperature
3.0 2.5 2.0 1.5 1.0 VIN = 2.8V TO 5.5V VIN1 = 1.8V
VIN1 Quiescent Current vs VIN1 Voltage
VIN = VIN1
IVIN (A)
-45C
3.0
3.5
4.0 VIN (V)
4.5
5.0
5.5
3.0
3.5
3672b1 G01
4.0 4.5 VIN1 (V)
5.0
5.5
0
3672b1 G02
25 50 75 100 125 150 TEMPERATURE (C)
3672b1 G03
Buck Regulated Output vs Temperature
1.845 BUCK REGULATED OUTPUT (V) 1.830 1.815 BUCK AT NO LOAD 1.800 1.785 1.770 1.755 -50 -25 BUCK AT 400mA LOAD VIN = 3.6V VIN1 = 1.8V LDO1 REGULATED OUTPUT (V) 1.23 1.22 1.21 1.20 1.19 1.18
LDO1 Regulated Output vs Temperature
VIN = 3.6V VIN1 = 1.8V LDO2 REGULATED OUTPUT (V) 2.87 2.85 2.83 2.81 2.79 2.77 2.75
LDO2 Regulated Output vs Temperature
VIN = 3.6V VIN1 = 1.8V
LDO1 AT NO LOAD
LDO2 AT NO LOAD LDO2 AT 150mA LOAD
LDO1 AT 150mA LOAD
0
25 50 75 100 125 150 TEMPERATURE (C)
3672b1 G04
1.17 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
3672b1 G05
2.73 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
3672b1 G06
Buck Regulated Output vs VIN Input Voltage
1.85 1.84 BUCK REGULATED OUTPUT (V) 1.83 1.82 1.81 1.80 1.79 1.78 1.77 1.76 1.75 2.5 3.0 3.5 4.0 4.5 5.0 VIN INPUT VOLTAGE (V) 5.5 BUCK AT 400mA LOAD BUCK AT NO LOAD BOTH LDOs UNLOADED LDO1 REGULATED OUTPUT (V) 1.23 1.22 1.21
LDO1 Regulated Output vs VIN1 Input Voltage
BUCK AND LDO2 UNLOADED VIN = 3.6V LDO2 REGULATED OUTPUT (V) 2.86 2.84 2.82 2.80 2.78 2.76
LDO2 Regulated Output Voltage vs VIN Input Voltage
BUCK AND LDO1 UNLOADED
ILDO1 = 0mA 1.20 1.19 1.18 1.17 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN1 INPUT VOLTAGE (V)
3672b1 G08
ILDO2 = 0mA ILDO2 = 150mA
ILDO1 = 150mA
2.74 2.5
3.0
3672b1 G07
3.5 4.0 4.5 5.0 VIN INPUT VOLTAGE (V)
5.5
3672b1 G09
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LTC3672B-1 TYPICAL PERFORMANCE CHARACTERISTICS
VIN1-LDO1 Dropout Voltage vs Load
600 500 DROPOUT VOLTAGE (mV) DROPOUT VOLTAGE (mV) 400 300 200 130C 100 0 25C 300 250 200 150 100 50 0 -45C LDO1 SHORT CIRCUIT CURRENT (mA)
TA = 25C unless otherwise specified.
VIN-LDO2 Dropout Voltage vs Load
500 450 400 350 300 250 200 150 100 50 0
LDO1 Short Circuit Current vs VIN1
VIN = 5.5V
130C 25C
-45C
-45C 25C 90C 0 1 2 3 VIN1 (V) 4 5 6
3672b1 G12
0
25
50 75 100 LDO1 LOAD (mA)
125
150
0
25
3672b1 G10
50 75 100 LDO2 LOAD (mA)
125
150
3672b1 G11
LDO1 Short Circuit Current vs VIN
500 LDO1 SHORT CIRCUIT CURRENT (mA) 400 300 200 100 0 2.5 LDO2 SHORT CIRCUIT CURRENT (mA) VIN1 = 1.8V 600 500 400 300 200 100
LDO2 Short Circuit Current vs VIN
2.6 2.5 FREQUENCY (MHz) 2.4 2.3 2.2 2.1 2.0
Buck Oscillator Frequency vs Temperature
VIN = 5.5V
VIN = 4.2V
VIN = 3.6V
-45C 25C 90C 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5
0 2.5
-45C 25C 90C 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5
VIN = 2.9V
3672b1 G13
3672b1 G14
1.9 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C)
3672b1 G15
PMOS Switch Maximum Peak Current
PMOS SWITCH MAX PEAK CURRENT (mA) 1000 PMOS ON-RESISTANCE (m) 900 800 900 700 600 500 400 300 200 100
Buck PMOS Switch On-Resistance
130C 90C 25C -45C ENALL OUTPUT VOLTAGES 500mV/DIV 0V 1V 0V
Startup Transient
VOUT3 VOUT1 VOUT1 VOUT2
800
50s/DIV
3672b1 G18
700 VIN = 2.9V VIN = 3.6V VIN = 5.5V
FRONT PAGE APPLICATION VIN = 3.6V 10mA RESISTIVE LOAD ON EACH OUTPUT 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5
600 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C)
3672b1 G16
0 2.5
3672b1 G17
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LTC3672B-1 PIN FUNCTIONS
SW (Pin 1): Switch Node Connection to Inductor. This pin connects to the drains of the buck regulator's main PMOS and synchronous NMOS switches. GND (Pin 2): Ground. ENALL (Pin 3): Enables all three outputs when high, shuts down the IC when low. This is a MOS gate input. An internal 5.5M resistor pulls this pin to ground. BUCKOUT (Pin 4): Output Voltage Sense Connection for the Buck Regulator. VIN1 (Pin 5): Power Input for the First Low Dropout Linear Regulator, LDO1. This pin may be connected to the buck regulator's output, VIN, or a voltage not exceeding VIN. LDO1 (Pin 6): Output of the First Low Dropout Linear Regulator. This pin must be bypassed to ground with a 1F or greater ceramic capacitor. LDO2 (Pin 7): Output of the Second Low Dropout Linear Regulator. This pin must be bypassed to ground with a 1F or greater ceramic capacitor. VIN (Pin 8): Input Bias Supply for the IC, and Power Input for the Buck Regulator and LDO2. This pin should be bypassed to ground with a 2.2F or greater ceramic capacitor. Exposed Pad (Pin 9): Ground. The Exposed Pad must be soldered to PCB.
BLOCK DIAGRAM
4 BUCKOUT 8 VIN 5 VIN1 LDO1 6 LDO2 7 1M GND 2 ENABLE BUCK 400k 2M
SW 1
2.25MHz OSC 800mV REFERENCE
LOGIC ENALL 3 5.5M
ENABLE LDO2 ENABLE LDO1 9 EXPOSED PAD (GND)
3672b1 BD
6
+ -
800k LDO2 LDO1 800k
400mA BUCK
800k
3672B1f
LTC3672B-1 OPERATION
INTRODUCTION The LTC3672B-1 combines a synchronous buck converter with two low dropout linear DC regulators (LDOs) to provide three low voltage outputs from a higher voltage input source. All outputs are enabled and disabled together through the ENALL pin. The output regulation voltages are set during manufacturing to 1.8V nominal for the buck, 1.2V nominal for LDO1, and 2.8V nominal for LDO2. LDO1 may be powered off of the buck output for higher overall efficiency. For versions of the IC with different output regulation voltages, consult the LTC factory. SYNCHRONOUS BUCK REGULATOR The synchronous buck uses a constant-frequency current mode architecture, switching at 2.25MHz down to very light loads, and supports no-load operation by skipping cycles. When the input voltage drops very close to or falls below the target output voltage, the buck supports 100% duty cycle operation (low dropout mode). Soft-start circuitry limits inrush current when powering on. Output current is limited in the event of an output short-circuit. The switch node is slew-rate limited to reduce EMI radiation. The buck regulation control-loop compensation is internal to the IC, and requires no external components. Main Control Loop An error amplifier monitors the difference between an internal reference voltage and the voltage on the BUCKOUT pin. When the BUCKOUT voltage is below the reference, the error amplifier output voltage increases. When the BUCKOUT voltage exceeds the reference, the error amplifier output voltage decreases. The error amplifier output controls the peak inductor current through the following mechanism: Paced by a free-running 2.25MHz oscillator, the main P-channel MOSFET switch is turned on at the start of the oscillator cycle. Current flows from the VIN supply through this PMOS switch, through the inductor via the SW pin, and into the output capacitor and load. When the current reaches the level programmed by the output of the error amplifier, the PMOS is shut off, and the N-channel MOSFET synchronous rectifier turns on. Energy stored in the inductor discharges into the load through this NMOS. The NMOS turns off at the end of the 2.25MHz cycle, or sooner, if the current through it drops to zero before the end of the cycle. Through these mechanisms, the error amplifier adjusts the peak inductor current to deliver the required output power to regulate the output voltage as sensed by the BUCKOUT pin. All necessary control-loop compensation is internal to the step-down switching regulator, requiring only a single ceramic output capacitor for stability. Light Load/No-Load Cycle-Skipping At light loads, the inductor current may reach zero before the end of the oscillator cycle, which will turn off the NMOS synchronous rectifier. In this case, the SW pin goes high impedance and will show damped "ringing". This is known as discontinuous operation, and is normal behavior for a switching regulator. At very light load and no-load conditions, the buck will automatically skip cycles as needed to maintain output regulation. Soft-Start Soft-start in the buck regulator is accomplished by gradually increasing the maximum allowed peak inductor current over a 200s period. This allows the output to rise slowly, controlling the inrush current required to charge up the output capacitor. A soft-start cycle occurs whenever the LTC3672B-1 is enabled, or after a fault condition has occurred (thermal shutdown or UVLO). Switch Slew-Rate Control The buck regulator contains new patent pending circuitry to limit the slew rate of the switch node (SW pin). This new circuitry is designed to transition the switch node over a period of a couple nanoseconds, significantly reducing radiated EMI and conducted supply noise while maintaining high efficiency. LOW VIN SUPPLY UNDERVOLTAGE LOCKOUT An undervoltage lockout (UVLO) circuit shuts down the LTC3672B-1 when VIN drops below about 1.7V.
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LTC3672B-1 OPERATION
LOW DROPOUT LINEAR REGULATORS (LDOS) The LTC3672B-1 contains two 150mA fixed-output LDO regulators. LDO1 takes power from the VIN1 pin and regulates a 1.2V output at the LDO1 pin. By connecting VIN1 to the buck regulator's 1.8V output, overall conversion efficiency can be improved, because the bulk of the stepdown will be done by the buck regulator at higher efficiency than what the LDO can do on its own. For example, for the case of deriving a 1.2V output from a 3.6V input (e.g. Lithium-Ion battery nominal voltage), using an LDO to do all of the step-down results in an efficiency of at most 1.2V/3.6V = 33.3%, using the fact that the upper-bound on any linear regulator's efficiency is output voltage divided by input voltage. Feeding the LDO from the output of the buck regulator, with a typical buck efficiency of 85%, raises the ceiling on overall efficiency to 85% * 1.2V/1.8V = 56.6%. This can increase battery life by up to 70%! LDO2 takes power straight from VIN and regulates a 2.8V output at the LDO2 pin. For stability, each LDO output must be bypassed to ground with a minimum 1F ceramic capacitor.
APPLICATIONS INFORMATION
BUCK REGULATOR INDUCTOR SELECTION Many different sizes and shapes of inductors are available from numerous manufacturers. Choosing the right inductor from such a large selection of devices can be overwhelming, but following a few basic guidelines will make the selection process much simpler. The buck regulator is designed to work with inductors in the range of 2.2H to 10H. A 4.7H inductor is a good starting point. Larger value inductors reduce ripple current, which improves output ripple voltage. Lower value inductors result in higher ripple current and improved transient response time. To maximize efficiency, choose an inductor with a low DC resistance. Choose an inductor with a DC current rating at least 1.5 times larger than the maximum load current to ensure that the inductor does not saturate during normal operation. If output short circuit is a possible condition, the inductor should be rated to handle the maximum peak current specified for the stepdown converters. Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or PermalloyTM materials are small and don't radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. Inductors that are very thin or have a very small volume typically have much higher core and DCR losses, and will not give the best efficiency. The choice of which style inductor to use often depends more on the price vs size, performance, and any radiated EMI requirements than on what the buck regulator needs to operate. Table 1 shows several inductors that work well with the buck regulator. These inductors offer a good compromise in current rating, DCR and physical size. Consult each manufacturer for detailed information on their entire selection of inductors.
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LTC3672B-1 APPLICATIONS INFORMATION
Table 1. Recommended Inductors for the Buck Regulator
INDUCTOR TYPE DB318C D312C DE2812C CDRH3D16 CDRH2D11 CLS4D09 SD3118 SD3112 SD12 SD10 LPS3015 * = Typical DCR L (H) 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 4.7 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 MAX IDC (A) 1.07 1.2 0.79 0.9 1.15 1.37 0.9 1.1 0.5 0.6 0.75 1.3 1.59 0.8 0.97 1.29 1.42 1.08 1.31 1.1 1.3 MAX DCR () 0.1 0.07 0.24 0.2 0.13* 0.105* 0.11 0.085 0.17 0.123 0.19 0.162 0.113 0.246 0.165 0.117* 0.104* 0.153* 0.108* 0.2 0.13 SIZE IN mm (L x W x H) 3.8 x 3.8 x 1.8 3.8 x 3.8 x 1.8 3.6 x 3.6 x 1.2 3.6 x 3.6 x 1.2 3 x 2.8 x 1.2 3 x 2.8 x 1.2 4 x 4 x 1.8 4 x 4 x 1.8 3.2 x 3.2 x 1.2 3.2 x 3.2 x 1.2 4.9 x 4.9 x 1 3.1 x 3.1 x 1.8 3.1 x 3.1 x 1.8 3.1 x 3.1 x 1.2 3.1 x 3.1 x 1.2 5.2 x 5.2 x 1.2 5.2 x 5.2 x 1.2 5.2 x 5.2 x 1 5.2 x 5.2 x 1 3 x 3 x 1.5 3 x 3 x 1.5 MANUFACTURER Toko www.toko.com
Sumida www.sumida.com
Cooper www.cooperet.com
Coil Craft www.coilcraft.com
INPUT/OUTPUT CAPACITOR SELECTION Low ESR (equivalent series resistance) ceramic capacitors should be used to bypass the following pins to ground: VIN, VIN1, the buck output, LDO1, and LDO2. Only X5R or X7R ceramic capacitors should be used because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. A 10F output capacitor is sufficient for the buck regulator output. For good transient response and stability the output capacitor for the buck regulator should retain at least 4F of capacitance over operating temperature and bias voltage. The VIN pin should be bypassed with a 2.2F capacitor. The LDO1 and LDO2 output pins should be bypassed with a 1F capacitor or greater. VIN1 should be bypassed with a 1F capacitor, which may be omitted if VIN1 is tied to the buck regulator's output capacitor.
Consult with capacitor manufacturers for detailed information on their selection and specifications of ceramic capacitors. Many manufacturers now offer very thin (<1mm tall) ceramic capacitors ideal for use in height-restricted designs. Table 2 shows a list of several ceramic capacitor manufacturers.
Table 2. Ceramic Capacitor Manufacturers
AVX Murata Taiyo Yuden Vishay Siliconix TDK www.avxcorp.com www.murata.com www.t-yuden.com www.vishay.com www.tdk.com
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LTC3672B-1 APPLICATIONS INFORMATION
PRINTED CIRCUIT BOARD LAYOUT CONSIDERATIONS When laying out the printed circuit board, the following list should be followed to ensure proper operation of the LTC3672B-1: 1) The Exposed Pad of the package should connect directly to a large ground plane to minimize thermal and electrical impedance. 2) The connections from the input supply pins (VIN and VIN1) to their respective decoupling capacitors should be kept as short as possible. The GND side of these capacitors should connect directly to the ground plane of the part. The VIN capacitor provides the AC current to the buck regulator's power MOSFETs and their drivers. It is especially important to minimize PCB trace inductance from this capacitor to the VIN and GND pins of the LTC3672B-1. 3) The switching power trace connecting the SW pin to the inductor should be kept as short as possible to reduce radiated EMI and parasitic coupling. 4) The LDO output capacitors should be placed as close to the IC as possible, and connect to the LDO outputs and the GND pin as directly as possible.
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LTC3672B-1 PACKAGE DESCRIPTION
DC Package 8-Lead Plastic DFN (2mm x 2mm)
(Reference LTC DWG # 05-08-1719 Rev O)
0.70 0.05 2.55 0.05 1.15 0.05 0.64 0.05 (2 SIDES) PACKAGE OUTLINE
0.25 0.05 0.45 BSC 1.37 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.05 TYP 2.00 0.10 (4 SIDES)
R = 0.115 TYP 5
8 0.40 0.10 PIN 1 NOTCH R = 0.20 OR 0.25 x 45 CHAMFER
(DC8) DFN 0106 REVO
PIN 1 BAR TOP MARK (SEE NOTE 6)
0.64 0.10 (2 SIDES)
4 0.200 REF 0.75 0.05 1.37 0.10 (2 SIDES) 0.00 - 0.05
0.23 0.05 0.45 BSC
1
BOTTOM VIEW--EXPOSED PAD
NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 0.15mm 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
3672B1f
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.
11
LTC3672B-1 TYPICAL APPLICATION
LTC3672B-1 with VIN1 Tied to VIN, VOUT1 Capable of 400mA Even with VOUT2 and VOUT3 Fully Loaded
VIN 2.9V TO 5.5V
LTC3672B-1 with VIN1 Tied to an Independent Supply, VOUT1 Capable of 400mA Even with VOUT2 and VOUT3 Fully Loaded
VIN 2.9V TO 5.5V 4.7 H SW BUCKOUT 10 F VOUT1 1.8V 400mA (250mA IF LDO1 FULLY-LOADED) VOUT2 1.2V 150mA VOUT3 2.8V UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS)
2.2 F
VIN VIN1 SW GND BUCKOUT LDO1 ENALL LTC3672B-1 LDO2
3672b1 TA02
4.7 H 10 F
VOUT1 1.8V 400mA VOUT2 1.2V 150mA VOUT3 2.8V UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS)
2.2 F
VIN GND 1F
LTC3672B-1 VIN1 ENALL LDO2
3672b1 TA03
ENABLE INPUT
1F
VIN1 1.8V TO VIN ENABLE INPUT
LDO1 1F
1F
1F
LTC3672B-1 with VIN1 Tied to Buckout with More LDO Output Capacitance for Improved Transient Response
VIN 2.9V TO 5.5V 4.7 H SW BUCKOUT VIN1 ENABLE INPUT LDO1 ENALL LTC3672B-1 LDO2
3672b1 TA04
Load Transient Response
10 F VOUT1 1.8V 400mA (250mA IF LDO1 FULLY-LOADED) VOUT2 1.2V 150mA VOUT3 2.8V UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS) VOUT2 50mV/DIV AC-COUPLED VOUT3 VOUT1 VOUT2 AND VOUT3 100mA LOAD CURRENT 10mA
10 F
VIN GND
4.7 F
4.7 F
20s/DIV VIN = 3.6V SIMULTANEOUS LOAD TRANSIENT ON BOTH LDOs VOUT1 FLOATING
3672b1 TA04b
RELATED PARTS
PART NUMBER LTC3405/LTC3405A LTC3406/LTC3406B LTC3407/LTC3407-2 LTC3410/LTC3410B LTC3411 LTC3445 LTC3446 LTC3448 DESCRIPTION 300mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converter 600mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converter Dual 600mA/800mA IOUT, 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converter 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converter 1.25A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter I2C Controllable 600mA Synchronous Buck Regulator with Two 50mA LDOs in a 4mm x 4mm QFN Synchronous 1A, 2.25MHz Step-Down DC/DC Regulator with Dual VLDOs 600A IOUT, 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converter with LDO Mode COMMENTS 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 20A, ISD <1A, ThinSOT Package 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20A, ISD <1A, ThinSOT Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD <1A, MS10E Package 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 26A, ISD <1A, SC70 Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60A, ISD <1A, MS10 Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.85V, IQ = 360A, ISD <27A, 4mm x 4mm QFN Package 95% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN) = 0.4V, IQ = 140A, ISD <1A, 3mm x 4mm DFN Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 32A, ISD <1A, MS10, DFN Packages 95% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN) = 0.4V, IQ = 85A, ISD <1A, 3mm x 3mm DFN Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD <1A, DFN-8 Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD <1A, MS10, DFN Packages
3672B1f LT 0607 * PRINTED IN USA
LTC3541/LTC3541-1/ Synchronous 500mA, 2.25MHz Step-Down DC/DC LTC3541-2/LTC3541-3 Regulator with a 300mA VLDO in a 3mm x 3mm DFN LTC3547 LTC3548/LTC3548-1/ LTC3548-2 Dual 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converter Dual 800mA/400mA IOUT, 2.25MHz, Synchronous StepDown DC/DC Converter
12 Linear Technology Corporation
(408) 432-1900
1630 McCarthy Blvd., Milpitas, CA 95035-7417
FAX: (408) 434-0507 www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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