LINEAR TECHNOLOGY LTC3707 Specifications and User Guide

LTC3707

High Efficiency, 2-Phase

Synchronous Step-Down Switching Regulator

FEATURES DESCRIPTIO 180° Phased Dual Controllers Reduce Required The LTC®3707 is a high performance dual step-down Input Capacitance and Power Supply Induced Noise switching regulator controller that drives N-channel syn- OPTI-LOOP® Compensation Minimizes COUT chronous power MOSFET stages. A constant frequency ±1.5% Output Voltage Accuracy over Temperature current mode architecture allows adjustment of the fre- Dual N-Channel MOSFET Synchronous Drive quency up to 300k Hz. Power loss and noise due to the ESR

Power Good Output Voltage Monitor of the input capacitors are minimized by operating the two DC Programmed Fixed Frequency 150k Hz to 300k Hz controller output stages out of phase.

Wide VIN Range: 4.5V to 28V Operation

OPTI-LOOP compensation allows the transient response

Very Low Dropout Operation: 99% Duty Cycle

to be optimized over a wide range of output capacitance and

Adjustable Soft-Start Current Ramping

ESR values. The precision 0.8V reference and power good

Foldback Output Current Limiting

output indicator are compatible with future microproces-

Latched Short-Circuit Shutdown with Defeat Option

sor generations, and a wide 3.5V to 30V input supply range

Output Overvoltage Protection

encompasses all battery chemistries.

Remote Output Voltage Sense

Low Shutdown IQ: 20µA A RUN/SS pin for each controller provides both soft-start 5V and 3.3V Standby Regulators and optional timed, short-circuit shutdown. Current Small 28-Lead Narrow SSOP Package foldback limits MOSFET dissipation during short-circuit Selectable Constant Frequency, Burst Mode® conditions when overcurrent latchoff is disabled. Output Operation or PWM Operation overvoltage protection circuitry latches on the bottom MOSFET until VOUT returns to normal. The FCB mode pin

APPLICATIO S can select among Burst Mode operation, constant fre-

quency mode and continuous inductor current mode or

Notebook and Palmtop Computers, PDAs

regulate a secondary winding.

Battery Chargers Portable Instruments Battery-Operated Digital Devices

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

DC Power Distribution Systems Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.

VIN TYPICAL APPLICATIO CIN 5.2V TO 28V

D4 CERAMIC 50V

VIN INTVCC

CERAMIC

M1 TG1 TG2 M3

L1 CB1, 0.1µF CB2, 0.1µF L2

6.3µH BOOST1 BOOST2 6.3µH

SW1 SW2 LTC3707

D1 M2 BG1 BG2 D2M4

SGND PGND

SENSE1+ SENSE2+

RSENSE1 RSENSE2

VOUT1 SENSE1– SENSE2– VOUT2

5V VOSENSE1 VOSENSE2 3.3V 5A R2 R4 5A

105k ITH1 ITH2

COUT1 CC1 CC2

1% R1 RUN/SS1 RUN/SS2 R3 1% +COUT

6V RC1 CSS1 CSS2 RC2 6V

SP 15k 0.1µF 0.1µF 15k SP

M1, M2, M3, M4: FDS6680A

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