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LT3684 36V, 2A, 2.8MHz Step-Down Switching Regulator FEATURES

DESCRIPTION
The LT(R)3684 is an adjustable frequency (300kHz to 2.8MHz) monolithic buck switching regulator that accepts input voltages up to 34V (36V maximum). A high efficiency 0.18 switch is included on the die along with a boost Schottky diode and the necessary oscillator, control and logic circuitry. Current mode topology is used for fast transient response and good loop stability. The LT3684's high operating frequency allows the use of small, low cost inductors and ceramic capacitors resulting in low output ripple while keeping total solution size to a minimum. The low current shutdown mode reduces input supply current to less than 1A while a resistor and capacitor on the RUN/SS pin provide a controlled output voltage ramp (soft-start). A power good flag signals when VOUT reaches 90% of the programmed output voltage. The LT3684 is available in 10-Pin MSOP and 3mm x 3mm DFN packages with Exposed Pads for low thermal resistance.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Wide Input Range: 3.6V to 34V Operating, 36V Maximum 2A Maximum Output Current Adjustable Switching Frequency: 300kHz to 2.8MHz Low Shutdown Current: IQ < 1A Integrated Boost Diode Power Good Flag Saturating Switch Design: 0.18 On-Resistance 1.265V Feedback Reference Voltage Output Voltage: 1.265V to 20V Soft-Start Capability Small 10-Pin Thermally Enhanced MSOP and (3mm x 3mm) DFN Packages
APPLICATIONS

Automotive Battery Regulation Power for Portable Products Distributed Supply Regulation Industrial Supplies Wall Transformer Regulation
TYPICAL APPLICATION
3.3V Step-Down Converter
VIN 4.5V TO 34V VIN OFF ON 16.2k 4.7F 330pF VC LT3684 RT PG 60.4k GND BIAS 324k FB 200k 22F 40 30 0 0.5 1 1.5 LOAD CURRENT (A) 2
3684 TA01b
Efficiency
VOUT 3.3V 2A 0.47F 90 80 70 60 50 VIN = 12V VOUT = 3.3V L = 4.7H f = 800kHz
BD BOOST SW 4.7H
RUN/SS
3684 TA01
EFFICIENCY (%)
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LT3684 ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, RUN/SS Voltage .................................................36V BOOST Pin Voltage ...................................................56V BOOST Pin Above SW Pin.........................................30V FB, RT, VC Voltage .......................................................5V BIAS, PG, BD Voltage ................................................30V Maximum Junction Temperature .......................... 125C
Operating Temperature Range (Note 2) LT3684E............................................... -40C to 85C LT3684I ............................................. -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) (MSE Only) ....................................................... 300C
PACKAGE/ORDER INFORMATION
TOP VIEW TOP VIEW BD BOOST SW VIN RUN/SS 1 2 3 4 5 11 10 RT 9 VC 8 FB 7 BIAS 6 PG BD BOOST SW VIN RUN/SS 1 2 3 4 5 10 9 8 7 6 RT VC FB BIAS PG
11
MSE PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125C, JA = 45C/W, JC = 10C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 125C, JA = 45C/W, JC = 10C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER LT3684EDD LT3684IDD
DD PART MARKING* LCVT LCVT
ORDER PART NUMBER LT3684EMSE LT3684IMSE
MSE PART MARKING* LTCVS LTCVS
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
ELECTRICAL CHARACTERISTICS
PARAMETER Minimum Input Voltage Quiescent Current from VIN
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 10V, VRUNS/SS = 10V, VBOOST = 15V, VBIAS = 3.3V unless otherwise noted. (Note 2)
CONDITIONS
MIN
TYP 3 0.01 0.4 1.2 0.01
MAX 3.6 0.5 0.8 2.0 0.5 1.5 0.1
UNITS V A mA mA A mA mA
VRUN/SS = 0.2V VBIAS = 3V, Not Switching VBIAS = 0, Not Switching
Quiescent Current from BIAS
VRUN/SS = 0.2V VBIAS = 3V, Not Switching VBIAS = 0, Not Switching
0.85 0
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LT3684 ELECTRICAL CHARACTERISTICS
PARAMETER Minimum Bias Voltage Feedback Voltage
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 10V, VRUNS/SS = 10V VBOOST = 15V, VBIAS = 3.3V unless otherwise noted. (Note 2)
CONDITIONS MIN 1.25 1.24 TYP 2.7 1.265 1.265 30 0.002 330 1000 75 100 3.5 2 RT = 8.66k RT = 29.4k RT = 187k
MAX 3 1.28 1.29 100 0.02
UNITS V V V nA %/V Mho A A A/V V
FB Pin Bias Current (Note 3) FB Voltage Line Regulation Error Amp gm Error Amp Gain VC Source Current VC Sink Current VC Pin to Switch Current Gain VC Clamp Voltage Switching Frequency 4V < VIN < 34V
2.7 1.25 250 3.1
3.0 1.4 300 100 3.6 360 0.02
3.3 1.55 350 150 4.0 2 2.1 30 10 0.2
MHz MHz kHz nS A mV A V mA A V V mV mV
Minimum Switch Off-Time Switch Current Limit Switch VCESAT Boost Schottky Reverse Leakage Minimum Boost Voltage (Note 4) BOOST Pin Current RUN/SS Pin Current RUN/SS Input Voltage High RUN/SS Input Voltage Low PG Threshold Offset from Feedback Voltage PG Hysteresis PG Leakage PG Sink Current VPG = 5V VPG = 0.4V VFB Rising ISW = 1A VRUN/SS = 2.5V Duty Cycle = 5% ISW = 2A VSW = 10V, VBIAS = 0V
1.6 18 5 2.5 100 10 0.1
1
A A
100
300
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 LT3684E 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. The LT3684I specifications are guaranteed over the -40C to 125C temperature range.
Note 3: Bias current measured in regulation. Bias current flows into the FB pin. Note 4: This is the minimum voltage across the boost capacitor needed to guarantee full saturation of the switch.
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LT3684 TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency (VOUT = 5.0V)
100 VIN = 12V VIN = 24V 80 90 85 80 EFFICIENCY (%) 75 70 65 60 L: NEC PLC-0745-4R7 f = 800kHz 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 LOAD CURRENT (A)
3684 G01
(TA = 25C unless otherwise noted) Efficiency
90 85 VIN = 12V
Efficiency (VOUT = 3.3V)
VIN = 7V
90 EFFICIENCY (%)
EFFICIENCY (%)
VIN = 24V
80 VIN = 12V VIN = 24V 75 70 65 60 L: NEC PLC-0745-4R7 f = 800kHz 55 50 0 0.5 VOUT = 3.3V L = 10H LOAD = 1A 1 2 2.5 1.5 SWITCHING FREQUENCY (MHz) 3
3684 G03
70
60
55 50 0
50
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 LOAD CURRENT (A)
3684 G02
Maximum Load Current
4.0 3.5 LOAD CURRENT (A) LOAD CURRENT (A) TYPICAL 3.0 2.5 2.0 1.5 1.0 5 10 25 20 15 INPUT VOLTAGE (V) 30
3684 G04
Maximum Load Current
4.0 3.5 TYPICAL 3.0 2.5 MINIMUM 2.0 1.5 1.0 5 10 25 20 15 INPUT VOLTAGE (V) 30
3684 G05
Switch Current Limit
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0 20 60 40 DUTY CYCLE (%) 80 100
3684 G06
MINIMUM
VOUT = 3.3V TA = 25C L = 4.7H f = 800kHz
VOUT = 5V TA = 25C L = 4.7H f = 800kHz
Switch Current Limit
4.5 4.0 SWITCH CURRENT LIMIT (A) 3.0 2.5 2.0 1.5 1.0 0.5 0 -50 -25 0 25 50 75 TEMPERATURE (C) 100 125 DUTY CYCLE = 90 % DUTY CYCLE = 10 % 600 500 400 300 200 100 0 700
Switch Voltage Drop
90 80 BOOST PIN CURRENT (mA) 70 60 50 40 30 20 10 0 0 500 1000 1500 2000 2500 3000 3500 SWITCH CURRENT (mA)
3684 G08
SWITCH CURRENT LIMIT (A)
Boost Pin Current
VOLTAGE DROP (mV)
0
500 1000 1500 2000 2500 3000 3500 SWITCH CURRENT (mA)
3684 G09
3684 G07
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LT3684 TYPICAL PERFORMANCE CHARACTERISTICS
Feedback Voltage
1.290 1.285 FEEDBACK VOLTAGE (V) 1.280 FREQUENCY (MHz) 1.275 1.270 1.265 1.260 1.255 1.250 -50 -25 0 25 50 75 TEMPERATURE (C) 100 125 1.20 1.15 1.10 1.05 1.00 0.95 0.90 0.85 0.80 -50 -25 0 25 50 75 TEMPERATURE (C) 100 125 SWITCHING FREQUENCY (kHz)
(TA = 25C unless otherwise noted) Frequency Foldback
1200 RT = 45.3k 1000 800 600 400 200 0 0 200 400 600 800 1000 1200 1400 FB PIN VOLTAGE (mV)
3684 G12
Switching Frequency
RT = 45.3k
3684 G10
3684 G11
Minimum Switch On-Time
140 MINIMUM SWITCH ON-TIME (ns) 120 SWITCH CURRENT LIMIT (A) 100 80 60 40 20 0 -50 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -25 25 0 50 75 TEMPERATURE (C) 100 125
Soft-Start
12 10 8 6 4 2 0 0 0.5 2 2.5 1.5 RUN/SS PIN VOLTAGE (V) 1 3 3.5
3684 G14
RUN/SS Pin Current
RUN/SS PIN CURRENT (A)
0
5
20 30 15 25 10 RUN/SS PIN VOLTAGE (V)
35
3684 G15
3684 G13
Boost Diode
1.6 1.4 VC PIN CURRENT (A) BOOST DIODE Vf (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 0 1.0 0.5 1.5 BOOST DIODE CURRENT (A) 2.0
3684 G16
Error Amp Output Current
100 80 60 40 20 0 -20 -40 -60 -80 1.065 1 .265 1.165 1.365 FB PIN VOLTAGE (V) 1.465
3684 G17
Minimum Input Voltage
4.5
4.0 INPUT VOLTAGE (V)
3.5
3.0 VOUT = 3.3V TA = 25C L = 4.7H f = 800kHz 0.1 0.01 1 LOAD CURRENT (A) 10
3684 G18
2.5
2.0 0.001
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LT3684 TYPICAL PERFORMANCE CHARACTERISTICS
Minimum Input Voltage
6.5 2.50
(TA = 25C unless otherwise noted) Power Good Threshold
1.200 PG RISING
VC Voltages
THRESHOLD VOLTAGE (V)
INPUT VOLTAGE (V)
CURRENT LIMIT CLAMP 1.50
THRESHOLD VOLTAGE (V) 100
6.0
2.00
1.180 1.160
5.5
5.0 VOUT = 5V TA = 25C L = 4.7H f = 800kHz 0.1 0.01 1 LOAD CURRENT (A) 10
3684 G19
1.00 SWITCHING THRESHOLD 0.50
1.140
4.5
1.120
4.0 0.001
0 -50
-25
0 50 25 75 TEMPERATURE (C)
125
1.100 -50
-25
0 50 25 75 TEMPERATURE (C)
100
125
3684 G20
3684 G21
Switching Waveforms (Discontinuous Operation)
IL 0.5A/DIV IL 0.5A/DIV
Switching Waveforms (Continuous Operation)
VSW 5V/DIV
VRUN/SS 5V/DIV
VOUT 10mV/DIV VIN = 12V, FRONT PAGE APPLICATION ILOAD = 140mA 1s/DIV
3684 G22
VOUT 10mV/DIV VIN = 12V, FRONT PAGE APPLICATION ILOAD = 1A 1s/DIV
3684 G23
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LT3684 PIN FUNCTIONS
BD (Pin 1): This pin connects to the anode of the boost Schottky diode. BOOST (Pin 2): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. SW (Pin 3): The SW pin is the output of the internal power switch. Connect this pin to the inductor, catch diode and boost capacitor. VIN (Pin 4): The VIN pin supplies current to the LT3684's internal regulator and to the internal power switch. This pin must be locally bypassed. RUN/SS (Pin 5): The RUN/SS pin is used to put the LT3684 in shutdown mode. Tie to ground to shut down the LT3684. Tie to 2.3V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. RUN/SS also provides a soft-start function; see the Applications Information section. PG (Pin 6): The PG pin is the open collector output of an internal comparator. PG remains low until the FB pin is within 10% of the final regulation voltage. PG output is valid when VIN is above 3.5V and RUN/SS is high. BIAS (Pin 7): The BIAS pin supplies the current to the LT3684's internal regulator. Tie this pin to the lowest available voltage source above 3V (typically VOUT). This architecture increases efficiency especially when the input voltage is much higher than the output. FB (Pin 8): The LT3684 regulates the FB pin to 1.265V. Connect the feedback resistor divider tap to this pin. VC (Pin 9): The VC pin is the output of the internal error amplifier. The voltage on this pin controls the peak switch current. Tie an RC network from this pin to ground to compensate the control loop. RT (Pin 10): Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency. Exposed Pad (Pin 11): Ground. The Exposed Pad must be soldered to PCB.
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LT3684 BLOCK DIAGRAM
VIN C1 7 INTERNAL 1.265V REF 4 VIN BIAS
5
RUN/SS
SLOPE COMP
10 RT
RT
OSCILLATOR 300kHz-2.8MHz
SOFT-START 6 PG ERROR AMP
+ -
GND 11
1.12V
+ -
FB
8 R2 R1
3684 BD
8
+ -
SWITCH LATCH R Q S VC CLAMP
BD
1
BOOST
2 C3
SW
L1 3 D1 C2 VOUT
VC
9 CC RC CF
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LT3684 OPERATION
The LT3684 is a constant frequency, current mode stepdown regulator. An oscillator, with frequency set by RT, enables an RS flip-flop, turning on the internal power switch. An amplifier and comparator monitor the current flowing between the VIN and SW pins, turning the switch off when this current reaches a level determined by the voltage at VC. An error amplifier measures the output voltage through an external resistor divider tied to the FB pin and servos the VC pin. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. An active clamp on the VC pin provides current limit. The VC pin is also clamped to the voltage on the RUN/SS pin; soft-start is implemented by generating a voltage ramp at the RUN/SS pin using an external resistor and capacitor. An internal regulator provides power to the control circuitry. The bias regulator normally draws power from the VIN pin, but if the BIAS pin is connected to an external voltage higher than 3V bias power will be drawn from the external source (typically the regulated output voltage). This improves efficiency. The RUN/SS pin is used to place the LT3684 in shutdown, disconnecting the output and reducing the input current to less than 1A. The switch driver operates from either the input or from the BOOST pin. An external capacitor and diode are used to generate a voltage at the BOOST pin that is higher than the input supply. This allows the driver to fully saturate the internal bipolar NPN power switch for efficient operation. The oscillator reduces the LT3684's operating frequency when the voltage at the FB pin is low. This frequency foldback helps to control the output current during startup and overload. The LT3684 contains a power good comparator which trips when the FB pin is at 90% of its regulated value. The PG output is an open-collector transistor that is off when the output is in regulation, allowing an external resistor to pull the PG pin high. Power good is valid when the LT3684 is enabled and VIN is above 3.6V.
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LT3684 APPLICATIONS INFORMATION
FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the 1% resistors according to: V R1= R2 OUT - 1 1.265 Reference designators refer to the Block Diagram. Setting the Switching Frequency The LT3684 uses a constant frequency PWM architecture that can be programmed to switch from 300kHz to 2.8MHz by using a resistor tied from the RT pin to ground. A table showing the necessary RT value for a desired switching frequency is in Figure 1.
SWITCHING FREQUENCY (MHz) 0.2 0.3 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 RT VALUE (k) 267 187 133 84.5 60.4 45.3 36.5 29.4 23.7 20.5 16.9 14.3 12.1 10.2 8.66
where VIN is the typical input voltage, VOUT is the output voltage, is the catch diode drop (~0.5V), VSW is the internal switch drop (~0.5V at max load). This equation shows that slower switching frequency is necessary to safely accommodate high VIN/VOUT ratio. Also, as shown in the next section, lower frequency allows a lower dropout voltage. The reason input voltage range depends on the switching frequency is because the LT3684 switch has finite minimum on and off times. The switch can turn on for a minimum of ~150ns and turn off for a minimum of ~150ns. This means that the minimum and maximum duty cycles are: DCMIN = fSW tON(MIN) DCMAX = 1- fSW tOFF(MIN) where fSW is the switching frequency, the tON(MIN) is the minimum switch on time (~150ns), and the tOFF(MIN) is the minimum switch off time (~150ns). These equations show that duty cycle range increases when switching frequency is decreased. A good choice of switching frequency should allow adequate input voltage range (see next section) and keep the inductor and capacitor values small. Input Voltage Range The maximum input voltage for LT3684 applications depends on switching frequency, the Absolute Maximum Ratings on VIN and BOOST pins, and on operating mode. If the output is in start-up or short-circuit operating modes, then VIN must be below 34V and below the result of the following equation: VIN(MAX ) = VOUT + VD -V +V fSW tON(MIN) D SW
Figure 1. Switching Frequency vs RT Value
Operating Frequency Tradeoffs Selection of the operating frequency is a tradeoff between efficiency, component size, minimum dropout voltage, and maximum input voltage. The advantage of high frequency operation is that smaller inductor and capacitor values may be used. The disadvantages are lower efficiency, lower maximum input voltage, and higher dropout voltage. The highest acceptable switching frequency (fSW(MAX)) for a given application can be calculated as follows: fSW(MAX ) = VD + VOUT tON(MIN) ( VD + VIN - VSW )
where VIN(MAX) is the maximum operating input voltage, VOUT is the output voltage, VD is the catch diode drop (~0.5V), VSW is the internal switch drop (~0.5V at max load), fSW is the switching frequency (set by RT), and tON(MIN) is the minimum switch on time (~150ns). Note that a higher switching frequency will depress the maximum operating input voltage. Conversely, a lower switching
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LT3684 APPLICATIONS INFORMATION
frequency will be necessary to achieve safe operation at high input voltages. If the output is in regulation and no short-circuit or start-up events are expected, then input voltage transients of up to 36V are acceptable regardless of the switching frequency. In this mode, the LT3684 may enter pulse skipping operation where some switching pulses are skipped to maintain output regulation. In this mode the output voltage ripple and inductor current ripple will be higher than in normal operation. The minimum input voltage is determined by either the LT3684's minimum operating voltage of ~3.6V or by its maximum duty cycle (see equation in previous section). The minimum input voltage due to duty cycle is: VIN(MIN) = VOUT + VD -V +V 1- fSW tOFF(MIN) D SW at least 3.5A at low duty cycles and decreases linearly to 2.5A at DC = 0.8. The maximum output current is a function of the inductor ripple current: IOUT(MAX) = ILIM - IL/2 Be sure to pick an inductor ripple current that provides sufficient maximum output current (IOUT(MAX)). The largest inductor ripple current occurs at the highest VIN. To guarantee that the ripple current stays below the specified maximum, the inductor value should be chosen according to the following equation: V +V V +V L = OUT D 1- OUT D VIN(MAX ) fIL where VD is the voltage drop of the catch diode (~0.4V), VIN(MAX) is the maximum input voltage, VOUT is the output voltage, fSW is the switching frequency (set by RT), and L is in the inductor value. The inductor's RMS current rating must be greater than the maximum load current and its saturation current should be about 30% higher. For robust operation in fault conditions (start-up or short circuit) and high input voltage (>30V), the saturation current should be above 3.5A. To keep the efficiency high, the series resistance (DCR) should be less than 0.1, and the core material should be intended for high frequency applications. Table 1 lists several vendors and suitable types.
Table 1. Inductor Vendors
VENDOR Murata TDK Toko URL www.murata.com www.componenttdk.com www.toko.com PART SERIES LQH55D SLF7045 SLF10145 D62CB D63CB D75C D75F Sumida www.sumida.com CR54 CDRH74 CDRH6D38 CR75 TYPE Open Shielded Shielded Shielded Shielded Shielded Open Open Shielded Shielded Open
where VIN(MIN) is the minimum input voltage, and tOFF(MIN) is the minimum switch off time (150ns). Note that higher switching frequency will increase the minimum input voltage. If a lower dropout voltage is desired, a lower switching frequency should be used. Inductor Selection For a given input and output voltage, the inductor value and switching frequency will determine the ripple current. The ripple current IL increases with higher VIN or VOUT and decreases with higher inductance and faster switching frequency. A reasonable starting point for selecting the ripple current is: IL = 0.4(IOUT(MAX)) where IOUT(MAX) is the maximum output load current. To guarantee sufficient output current, peak inductor current must be lower than the LT3684's switch current limit (ILIM). The peak inductor current is: IL(PEAK) = IOUT(MAX) + IL/2 where IL(PEAK) is the peak inductor current, IOUT(MAX) is the maximum output load current, and IL is the inductor ripple current. The LT3684's switch current limit (ILIM) is
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LT3684 APPLICATIONS INFORMATION
Of course, such a simple design guide will not always result in the optimum inductor for your application. A larger value inductor provides a slightly higher maximum load current and will reduce the output voltage ripple. If your load is lower than 2A, then you can decrease the value of the inductor and operate with higher ripple current. This allows you to use a physically smaller inductor, or one with a lower DCR resulting in higher efficiency. There are several graphs in the Typical Performance Characteristics section of this data sheet that show the maximum load current as a function of input voltage and inductor value for several popular output voltages. Low inductance may result in discontinuous mode operation, which is okay but further reduces maximum load current. For details of maximum output current and discontinuous mode operation, see Linear Technology Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5), there is a minimum inductance required to avoid subharmonic oscillations. See AN19. Input Capacitor Bypass the input of the LT3684 circuit with a ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage, and should not be used. A 4.7F to 10F ceramic capacitor is adequate to bypass the LT3684 and will easily handle the ripple current. Note that larger input capacitance is required when a lower switching frequency is used. If the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT3684 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 4.7F capacitor is capable of this task, but only if it is placed close to the LT3684 and the catch diode (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT3684. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT3684 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3684's voltage rating. This situation is easily avoided (see the Hot Plugging Safety section). For space sensitive applications, a 2.2F ceramic capacitor can be used for local bypassing of the LT3684 input. However, the lower input capacitance will result in increased input current ripple and input voltage ripple, and may couple noise into other circuitry. Also, the increased voltage ripple will raise the minimum operating voltage of the LT3684 to ~3.7V. Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT3684 to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3684's control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: COUT = 100 VOUT fSW
where fSW is in MHz, and COUT is the recommended output capacitance in F. Use X5R or X7R types. This choice will provide low output ripple and good transient response. Transient performance can be improved with a higher value capacitor if the compensation network is also adjusted to maintain the loop bandwidth. A lower value of output capacitor can be used to save space and cost but transient performance will suffer. See the Frequency Compensation section to choose an appropriate compensation network.
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LT3684 APPLICATIONS INFORMATION
Table 2. Capacitor Vendors
VENDOR Panasonic PHONE (714) 373-7366 URL www.panasonic.com PART SERIES Ceramic, Polymer, Tantalum Kemet Sanyo (864) 963-6300 (408) 749-9714 www.kemet.com www.sanyovideo.com Ceramic, Tantalum Ceramic, Polymer, Tantalum Murata AVX Taiyo Yuden (864) 963-6300 (408) 436-1300 www.murata.com www.avxcorp.com www.taiyo-yuden.com Ceramic Ceramic, Tantalum Ceramic TPS Series POSCAP T494, T495 EEF Series COMMANDS
When choosing a capacitor, look carefully through the data sheet to find out what the actual capacitance is under operating conditions (applied voltage and temperature). A physically larger capacitor, or one with a higher voltage rating, may be required. High performance tantalum or electrolytic capacitors can be used for the output capacitor. Low ESR is important, so choose one that is intended for use in switching regulators. The ESR should be specified by the supplier, and should be 0.05 or less. Such a capacitor will be larger than a ceramic capacitor and will have a larger capacitance, because the capacitor must be large to achieve low ESR. Table 2 lists several capacitor vendors. Catch Diode The catch diode conducts current only during switch off time. Average forward current in normal operation can be calculated from: ID(AVG) = IOUT (VIN - VOUT)/VIN where IOUT is the output load current. The only reason to consider a diode with a larger current rating than necessary for nominal operation is for the worst-case condition of shorted output. The diode current will then increase to the typical peak switch current. Peak reverse voltage is equal to the regulator input voltage. Use a diode with a reverse voltage rating greater than the input voltage. Table 3 lists several Schottky diodes and their manufacturers.
Table 3. Diode Vendors
PART NUMBER On Semicnductor MBRM120E MBRM140 Diodes Inc. B120 B130 B220 B230 DFLS240L International Rectifier 10BQ030 20BQ030 VR (V) 20 40 20 30 20 30 40 30 30 IAVE (A) 1 1 1 1 2 2 2 1 2 VF AT 1A (mV) 530 550 500 500 500 500 500 420 470 470 VF AT 2A (mV) 595
Frequency Compensation The LT3684 uses current mode control to regulate the output. This simplifies loop compensation. In particular, the LT3684 does not require the ESR of the output capacitor for stability, so you are free to use ceramic capacitors to achieve low output ripple and small circuit size. Frequency compensation is provided by the components tied to the VC pin, as shown in Figure 2. Generally a capacitor (CC) and a resistor (RC) in series to ground are used. In addition, there may be lower value capacitor in parallel. This capacitor (CF) is not part of the loop compensation but is used to filter noise at the switching frequency, and is required only if a phase-lead capacitor is used or if the output capacitor has high ESR.
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LT3684 APPLICATIONS INFORMATION
LT3684 CURRENT MODE POWER STAGE gm = 3.5mho SW ERROR AMPLIFIER FB ESR gm = 330mho 3M C1 POLYMER OR TANTALUM R2 CERAMIC 10s/DIV R1 CPL OUTPUT IL 1A/DIV VOUT = 12V, FRONT PAGE APPLICATION
VC RC CC
CF
Figure 2. Model for Loop Response
Loop compensation determines the stability and transient performance. Designing the compensation network is a bit complicated and the best values depend on the application and in particular the type of output capacitor. A practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the compensation network to optimize the performance. Stability should then be checked across all operating conditions, including load current, input voltage and temperature. The LT1375 data sheet contains a more thorough discussion of loop compensation and describes how to test the stability using a transient load. Figure 2 shows an equivalent circuit for the LT3684 control loop. The error amplifier is a transconductance amplifier with finite output impedance. The power section, consisting of the modulator, power switch and inductor, is modeled as a transconductance amplifier generating an output current proportional to the voltage at the VC pin. Note that the output capacitor integrates this current, and that the capacitor on the VC pin (CC) integrates the error amplifier output current, resulting in two poles in the loop. In most cases a zero is required and comes from either the output capacitor ESR or from a resistor RC in series with CC. This simple model works well as long as the value of the inductor is not too high and the loop crossover frequency is much lower than the switching frequency. A phase lead capacitor (CPL) across the feedback divider
14
- +
1.265V
+
C1
VOUT 100mV/DIV
GND
3684 F03
Figure 3. Transient Load Response of the LT3684 Front Page Application as the Load Current is Stepped from 500mA to 1500mA. VOUT = 3.3V
3684 F02
may improve the transient response. Figure 3 shows the transient response when the load current is stepped from 500mA to 1500mA and back to 500mA. BOOST and BIAS Pin Considerations Capacitor C3 and the internal boost Schottky diode (see the Block Diagram) are used to generate a boost voltage that is higher than the input voltage. In most cases a 0.22F capacitor will work well. Figure 2 shows three ways to arrange the boost circuit. The BOOST pin must be more than 2.3V above the SW pin for best efficiency. For outputs of 3V and above, the standard circuit (Figure 4a) is best. For outputs between 2.8V and 3V, use a 1F boost capacitor. A 2.5V output presents a special case because it is marginally adequate to support the boosted drive stage while using the internal boost diode. For reliable BOOST pin operation with 2.5V outputs use a good external Schottky diode (such as the ON Semi MBR0540), and a 1F boost capacitor (see Figure 4b). For lower output voltages the boost diode can be tied to the input (Figure 4c), or to another supply greater than 2.8V. The circuit in Figure 4a is more efficient because the BOOST pin current and BIAS pin quiescent current comes from a lower voltage source. You must also be sure that the maximum voltage ratings of the BOOST and BIAS pins are not exceeded. The minimum operating voltage of an LT3684 application is limited by the minimum input voltage (3.6V) and by the maximum duty cycle as outlined in a previous section. For
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LT3684 APPLICATIONS INFORMATION
VOUT BD BOOST C3 SW INPUT VOLTAGE (V) VIN VIN LT3684 5.0 4.5 4.0 TO RUN 3.5 3.0 VOUT = 3.3V TA = 25C L = 4.7H f = 800kHz 0.1 0.01 1 LOAD CURRENT (A) 10 6.0 TO START 5.5
4.7F
GND
(4a) For VOUT > 2.8V
VOUT BD BOOST VIN VIN LT3684 SW INPUT VOLTAGE (V) C3 D2
2.5 2.0 0.001
8.0 TO START 7.0
4.7F
GND
6.0 5.0 TO RUN 4.0 3.0 2.0 0.001 VOUT = 5V TA = 25C L = 4.7H f = 800kHz 0.1 0.01 1 LOAD CURRENT (A) 10
3684 F05
(4b) For 2.5V < VOUT < 2.8V
VOUT BD BOOST VIN VIN LT3684 SW C3
4.7F
GND
Figure 5. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit
3684 FO4
(4c) For VOUT < 2.5V Figure 4. Three Circuits For Generating The Boost Voltage
proper start-up, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3684 is turned on with its RUN/SS pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly. This minimum load will depend on input and output voltages, and on the arrangement of the boost circuit. The minimum load generally goes to zero once the circuit has started. Figure 5 shows a plot of minimum load to start and to run as a function of input
voltage. In many cases the discharged output capacitor will present a load to the switcher and the minimum input to start will be the same as the minimum input to run. This occurs, for example, if RUN/SS is asserted after VIN is applied. The plots show the worst-case situation where VIN is ramping very slowly. For lower start-up voltage, the boost diode can be tied to VIN; however, this restricts the input range to one-half of the absolute maximum rating of the BOOST pin. At light loads, the inductor current becomes discontinuous and the effective duty cycle can be very high. This reduces the minimum input voltage to approximately 300mV above VOUT. At higher load currents, the inductor current is continuous and the duty cycle is limited by the maximum duty cycle of the LT3684, requiring a higher input voltage to maintain regulation.
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15
LT3684 APPLICATIONS INFORMATION
Soft-Start The RUN/SS pin can be used to soft-start the LT3684, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC filter to create a voltage ramp at this pin. Figure 7 shows the startup and shut-down waveforms with the soft-start circuit. By choosing a large RC time constant, the peak start-up current can be reduced to the current that is required to regulate the output, with no overshoot. Choose the value of the resistor so that it can supply 20A when the RUN/SS pin reaches 2.3V.
VIN D4 MBRS140 VIN RUN/SS VC GND FB BACKUP BOOST LT3684 SW VOUT
3684 F07
Figure 7. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output. It Also Protects the Circuit from a Reversed Input. The LT3684 Runs Only When the Input is Present
RUN 15k RUN/SS 0.22F GND
IL 1A/DIV
VRUN/SS 2V/DIV VOUT 2V/DIV
LT3684 can pull large currents from the output through the SW pin and the VIN pin. Figure 7 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 8 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT3684's VIN and SW pins, the catch diode (D1) and the input capacitor (C1). The loop formed by these components should be as small as possible. These components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane below these components. The SW and BOOST nodes should be as small as possible. Finally, keep the FB and VC nodes small so that the ground traces will shield them from the SW and BOOST nodes. The Exposed Pad on the bottom of the package must be soldered to ground so that the pad acts as a heat sink. To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT3684 to additional ground planes within the circuit board and on the bottom side.
2ms/DIV
3481 F06
Figure 6. To Soft-Start the LT3684, Add a Resisitor and Capacitor to the RUN/SS Pin
Shorted and Reversed Input Protection If the inductor is chosen so that it won't saturate excessively, an LT3684 buck regulator will tolerate a shorted output. There is another situation to consider in systems where the output will be held high when the input to the LT3684 is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode OR-ed with the LT3684's output. If the VIN pin is allowed to float and the RUN/SS pin is held high (either by a logic signal or because it is tied to VIN), then the LT3684's internal circuitry will pull its quiescent current through its SW pin. This is fine if your system can tolerate a few mA in this state. If you ground the RUN/SS pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the
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16
LT3684 APPLICATIONS INFORMATION
L1 VOUT C2
RRT
CC
RC R2 R1
D1
C1 GND RPG
3684 F08
VIAS TO LOCAL GROUND PLANE VIAS TO VOUT
VIAS TO RUN/SS VIAS TO PG
VIAS TO VIN OUTLINE OF LOCAL GROUND PLANE
Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation
Hot Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3684 circuits. However, these capacitors can cause problems if the LT3684 is plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion). The low loss ceramic capacitor, combined with stray inductance in series with the power source, forms an under damped tank circuit, and the voltage at the VIN pin of the LT3684 can ring to twice the nominal input voltage, possibly exceeding the LT3684's rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3684 into an energized supply, the input network should be designed to prevent this overshoot. Figure 9 shows the waveforms that result when an LT3684 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The first plot is the response with a 4.7F ceramic capacitor at the input. The input voltage rings as high as 50V and the input current peaks at 26A. A good solution is shown in Figure 9b. A 0.7 resistor is added in series with the
input to eliminate the voltage overshoot (it also reduces the peak input current). A 0.1F capacitor improves high frequency filtering. For high input voltages its impact on efficiency is minor, reducing efficiency by 1.5 percent for a 5V output at full load operating from 24V. High Temperature Considerations The PCB must provide heat sinking to keep the LT3684 cool. The Exposed Pad on the bottom of the package must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these layers will spread the heat dissipated by the LT3684. Place additional vias can reduce thermal resistance further. With these steps, the thermal resistance from die (or junction) to ambient can be reduced to JA = 35C/W or less. With 100 LFPM airflow, this resistance can fall by another 25%. Further increases in airflow will lead to lower thermal resistance. Because of the large output current capability of the LT3684, it is possible to dissipate enough heat to raise the junction temperature beyond the absolute maximum of 125C. When operating at high ambient temperatures, the
3684f
17
LT3684 APPLICATIONS INFORMATION
CLOSING SWITCH SIMULATES HOT PLUG IIN VIN LT3684 DANGER VIN 20V/DIV RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING
+
4.7F
LOW IMPEDANCE ENERGIZED 24V SUPPLY
STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR
IIN 10A/DIV 20s/DIV
(9a)
0.7 LT3684 VIN 20V/DIV
+
0.1F 4.7F IIN 10A/DIV
(9b)
20s/DIV
LT3684
VIN 20V/DIV
+
22F 35V AI.EI.
+
4.7F IIN 10A/DIV
(9c)
20s/DIV
3684 F09
Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation when the LT3684 is Connected to a Live Supply
maximum load current should be derated as the ambient temperature approaches 125C. Power dissipation within the LT3684 can be estimated by calculating the total power loss from an efficiency measurement and subtracting the catch diode loss and inductor loss. The die temperature is calculated by multiplying the LT3684 power dissipation by the thermal resistance from junction to ambient.
Other Linear Technology Publications Application Notes 19, 35 and 44 contain more detailed descriptions and design information for buck regulators and other switching regulators. The LT1376 data sheet has a more extensive discussion of output ripple, loop compensation and stability testing. Design Note 100 shows how to generate a bipolar output supply using a buck regulator.
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18
LT3684 TYPICAL APPLICATIONS
5V Step-Down Converter
VOUT 5V 2A VIN ON OFF RUN/SS BD BOOST 0.47F 4.7F 20k 60.4k 330pF f = 800kHz D: DIODES INC. DFLS240L L: TAIYO YUDEN NP06DZB6R8M VC RT PG GND BIAS 590k FB 200k
3684 TA02
VIN 6.3V TO 34V
L 6.8H
LT3684
SW D
22F
3.3V Step-Down Converter
VIN 4.4V TO 34V VIN ON OFF RUN/SS BD BOOST 0.47F 4.7F 16.2k 60.4k 330pF f = 800kHz D: DIODES INC. DFLS240L L: TAIYO YUDEN NP06DZB4R7M VC RT PG GND BIAS 324k FB 200k
3684 TA03
VOUT 3.3V 2A
L 4.7H
LT3684
SW D
22F
3684f
19
LT3684 TYPICAL APPLICATIONS
2.5V Step-Down Converter
VOUT 2.5V 2A VIN ON OFF RUN/SS BD BOOST 1mF 4.7mF 22.1k 84.5k 220pF f = 600kHz D1: DIODES INC. DFLS240L D2: MBR0540 L: TAIYO YUDEN NP06DZB4R7M VC RT PG GND BIAS 196k FB 200k
3684 TA04
VIN 4V TO 34V D2 L 4.7mH D1
LT3684
SW
47mF
5V, 2MHz Step-Down Converter
VIN 8.6V TO 22V TRANSIENT TO 36V VIN ON OFF RUN/SS BD BOOST 0.47mF 2.2mF 20k 16.9k 330pF f = 2MHz D: DIODES INC. DFLS240L L: SUMIDA CDRH4D22/HP-2R2 VC RT PG GND BIAS 590k FB 200k
3684 TA05
VOUT 5V 2A
L 2.2mH
LT3684
SW D
10mF
3684f
20
LT3684 TYPICAL APPLICATIONS
12V Step-Down Converter
VIN 15V TO 34V VIN ON OFF RUN/SS BD BOOST 0.47F 10F 30k 60.4k 330pF f = 800kHz D: DIODES INC. DFLS240L L: NEC/TOKIN PLC-0755-100 VC RT PG GND BIAS 845k FB 100k
3684 TA06
VOUT 12V 2A
L 10H
LT3684
SW D
22F
1.8V Step-Down Converter
VIN 3.5V TO 27V VIN ON OFF RUN/SS BD BOOST 0.47F 4.7F 15.4k 105k 330pF f = 500kHz D: DIODES INC. DFLS240L L: TAIYO YUDEN NP06DZB3R3M VC RT PG GND BIAS 84.5k FB 200k
3684 TA07
VOUT 1.8V 2A
L 3.3H
LT3684
SW D
47F
3684f
21
LT3684 PACKAGE DESCRIPTION
DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
0.675 0.05
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 6 0.38 0.10 10
3.00 0.10 (4 SIDES) PIN 1 TOP MARK (SEE NOTE 6)
1.65 0.10 (2 SIDES)
(DD) DFN 1103
5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES)
1
0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 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
3684f
22
LT3684 PACKAGE DESCRIPTION
MSE Package 10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1664)
BOTTOM VIEW OF EXPOSED PAD OPTION
2.794 0.102 (.110 .004)
0.889 0.127 (.035 .005)
1
2.06 0.102 (.081 .004) 1.83 0.102 (.072 .004)
5.23 (.206) MIN
2.083 0.102 3.20 - 3.45 (.082 .004) (.126 - .136)
10
0.50 0.305 0.038 (.0197) (.0120 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
3.00 0.102 (.118 .004) (NOTE 3) 10 9 8 7 6
0.497 0.076 (.0196 .003) REF
4.90 0.152 (.193 .006) 0.254 (.010) GAUGE PLANE 0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) SEATING PLANE 1.10 (.043) MAX DETAIL "A" 0 - 6 TYP 12345
3.00 0.102 (.118 .004) (NOTE 4)
0.86 (.034) REF
0.50 (.0197) NOTE: BSC 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.17 - 0.27 (.007 - .011) TYP
0.127 0.076 (.005 .003)
MSOP (MSE) 0603
3684f
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.
23
LT3684 TYPICAL APPLICATION
1.265V Step-Down Converter
VOUT 1.265V 2A VIN ON OFF RUN/SS BD BOOST 0.47mF 4.7mF 13k 105k 330pF f = 500kHz
3648 TA08
VIN 3.6V TO 27V
L 3.3mH
VC RT PG
LT3648
SW D BIAS
GND
FB 47mF
D: DIODES INC. DFLS240L L: TAIYO YUDEN NP06DZB3R3M
RELATED PARTS
PART NUMBER LT1933 LT3437 LT1936 LT3493 LT1976/LT1977 LT1767 LT1940 LT1766 LT3434/LT3435 LT3481 DESCRIPTION 500mA (IOUT), 500kHz Step-Down Switching Regulator in SOT-23 60V, 400mA (IOUT), MicroPower Step-Down DC/DC Converter with Burst Mode Operation 36V, 1.4A (IOUT), 500kHz High Efficiency Step-Down DC/DC Converter 36V, 1.2A (IOUT), 750kHz High Efficiency Step-Down DC/DC Converter 60V, 1.2A (IOUT), 200kHz/500kHz, High Efficiency StepDown DC/DC Converter with Burst Mode Operation 25V, 1.2A (IOUT), 1.1MHz, High Efficiency Step-Down DC/DC Converter COMMENTS VIN: 3.6V to 36V, VOUT(MIN) = 12V, IQ = 1.6mA, ISD < 1A, ThinSOTTM Package VIN: 3.3V to 80V, VOUT(MIN) = 1.25V, IQ = 100A, ISD < 1A, DFN Package VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.9mA, ISD < 1A, MS8E Package VIN: 3.6V to 40V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1A, DFN Package VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100A, ISD < 1A, TSSOP16E Package VIN: 3V to 25V, VOUT(MIN) = 1.20V, IQ = 1mA, ISD < 6A, MS8E Package
Dual 25V, 1.4A (IOUT), 1.1MHz, High Efficiency Step-Down VIN: 3.6V to 25V, VOUT(MIN) = 1.20V, IQ = 3.8mA, ISD < 30A, TSSOP16E DC/DC Converter Package 60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter 60V, 2.4A (IOUT), 200/500kHz, High Efficiency Step-Down DC/DC Converter with Burst Mode Operation 36V, 2A (IOUT), Micropower 2.8MHz, High Efficiency Step-Down DC/DC Converter VIN: 5.5V to 60V, VOUT(MIN) = 1.20V, IQ = 2.5mA, ISD < 25A, TSSOP16E Package VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100A, ISD < 1A, TSSOP16E Package VIN: 3.6V to 36V, VOUT(MIN) = 1.265V, IQ = 5A, ISD < 1A, 3mm x 3mm DFN and MS10E Packages
3684f
24 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0207 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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