LTC3707

1

3707fb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

High Efficiency, 2-Phase

Synchronous Step-Down

Switching Regulator

The LTC

switching regulator controller that drives N-channel

synchronous power MOSFET stages. A constant frequency

current mode architecture allows adjustment of the

frequency 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 microprocessor

generations, and a wide 3.5V to 30V 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

pin can select among Burst Mode operation, constant

frequency mode and continuous inductor current mode

or regulate a secondary winding.

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

■

180° Phased Dual Controllers Reduce Required

Input Capacitance and Power Supply Induced Noise

■

OPTI-LOOP

■

±1.5% Output Voltage Accuracy over Temperature

■

Dual N-Channel MOSFET Synchronous Drive

■

Power Good Output Voltage Monitor

■

DC Programmed Fixed Frequency 150kHz to 300kHz

■

■

Very Low Dropout Operation: 99% Duty Cycle

■

Adjustable Soft-Start Current Ramping

■

Foldback Output Current Limiting

■

Latched Short-Circuit Shutdown with Defeat Option

■

Output Overvoltage Protection

■

Remote Output Voltage Sense

■

■

5V and 3.3V Standby Regulators

■

Operation or PWM Operation

■

Small 28-Lead Narrow SSOP Package

■

Notebook and Palmtop Computers, PDAs

■

Battery Chargers

■

Portable Instruments

■

Battery-Operated Digital Devices

■

DC Power Distribution Systems

L, LT, LTC, LTM, Burst Mode, and OPTI-LOOP are registered 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, 6304066, 6580258.

+

4.7μF

D3

D4

D1

M2

M1

R2

105k

1%

1000pF

L1

6.3μH

220pF

1μF

CERAMIC

22μF

50V

CERAMIC

+

47μF

6V

SP

0.01Ω

R1

20k

1%

15k

5V

5A

D2

M4

M3

R4

63.4k

1%

L2

6.3μH

220pF

1000pF

+

56μF

6V

SP

0.01Ω

R3

20k

1%

15k

3.3V

5A

TG1

TG2

BOOST1

BOOST2

SW1

SW2

BG1

BG2

SGND

PGND

RUN/SS1

RUN/SS2

5.2V TO 28V

M1, M2, M3, M4: FDS6680A

3707 F01

0.1μF

0.1μF

LTC3707