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LTC3707-SYNC

High Efficiency, 2-Phase Synchronous Step-Down Switching Regulator

Linear Technology 

LTC3707-SYNC

High Efficiency, 2-Phase

Synchronous Step-Down Switching Regulator

FEATURES

s 180° Phased Controllers Reduce Required Input

Capacitance and Power Supply Induced Noise

s OPTI-LOOP® Compensation Minimizes COUT

s Dual N-Channel MOSFET Synchronous Drive

s ±1.5% Output Voltage Accuracy

s Power Good Output Voltage Monitor

s Phase-Lockable Fixed Frequency 150kHz to 300kHz

s Wide VIN Range: 4.5V to 28V Operation

s Very Low Dropout Operation: 99% Duty Cycle

s Adjustable Soft-Start Current Ramping

s Foldback Output Current Limiting

s Latched Short-Circuit Shutdown with Defeat Option

s Output Overvoltage Protection

s Remote Output Voltage Sense

s Low Shutdown IQ: 20µA

s 5V and 3.3V Standby Regulators

s Small 28-Lead Narrow SSOP Package (0.150" Wide)

s Selectable Constant Frequency, Burst Mode® or

PWM Operation

U

APPLICATIO S

s Notebook and Palmtop Computers, PDAs

s Telecom Systems

s Portable Instruments

s Battery-Operated Digital Devices

s DC Power Distribution Systems

DESCRIPTIO

The LTC®3707-SYNC is a high performance dual step-

down switching regulator controller that drives all

N-channel synchronous power MOSFET stages. A con-

stant frequency current mode architecture allows phase-

lockable frequency of up to 300kHz. Power loss and noise

due to the ESR of the input capacitors are minimized by

operating the two controller output stages out of phase.

OPTI-LOOP compensation allows the transient response

to be optimized over a wide range of output capacitance and

ESR values. The precision 0.8V reference and power good

output indicator are compatible with future microproces-

sor generations, and a wide 4.5V to 28V (30V maximum)

input supply range encompasses all battery chemistries.

A RUN/SS pin for each controller provides both soft-start

and optional timed, short-circuit shutdown. Current

foldback limits MOSFET dissipation during short-circuit

conditions when overcurrent latchoff is disabled. Output

overvoltage protection circuitry latches on the bottom

MOSFET until VOUT returns to normal. The FCB mode pin

can select among Burst Mode, constant frequency mode

and continuous inductor current mode or regulate a

secondary winding. The IC includes a power good output

pin that indicates when both outputs are within 7.5% of

their designed set point.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATIO

L1

6.3µH

D1

VOUT1

5V

5A

+

RSENSE1

0.01Ω

COUT1

47µF

6V

SP

R2

105k

1%

+

4.7µF

M1

CB1, 0.1µF

M2

D3

VIN PGOOD INTVCC

TG1

TG2

BOOST1

BOOST2

SW1

SW2

LTC3707-SYNC

BG1

BG2

1µF

D4

CERAMIC

M3

CB2, 0.1µF

M4

fIN

1000pF

PLLIN

SENSE1+

SENSE1–

PGND

SENSE2+

SENSE2–

1000pF

VOSENSE1

VOSENSE2

ITH1

ITH2

R1

CC1

220pF

RUN/SS1 SGND RUN/SS2

CC2

220pF

R3

20k

1%

RC1

15k

CSS1

0.1µF

CSS2

RC2

0.1µF

15k

20k

1%

VIN

CIN 5.2V TO 28V

22µF

50V

CERAMIC

L2

6.3µH

D2

RSENSE2

0.01Ω

R4

63.4k

1%

COUT

56µF

6V

SP

VOUT2

3.3V

5A

M1, M2, M3, M4: FDS6680A

3707 F01

Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter

3707sf

1

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