LTC3707EGN High Effi ciency,2-Phase Synchronous Step-Down Switching Regulator

FEATURES

180° Phased Dual Controllers Reduce Required Input Capacitance and Power Supply Induced Noise

OPTI-LOOP® Compensation Minimizes COUT

±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

Wide VIN Range: 4.5V to 28V Operation

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

Low Shutdown IQ: 20μA

5V and 3.3V Standby Regulators

Selectable Constant Frequency, Burst Mode® Operation or PWM Operation

Small 28-Lead Narrow SSOP Package

APPLICATIONS

Notebook and Palmtop Computers, PDAs

Battery Chargers

Portable Instruments

Battery-Operated Digital Devices

DC Power Distribution Systems

DESCRIPTION

The LTC®3707 is a high performance dual step-down 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 MOSFET until VOUT returns to normal. The FCB mode pin can select among Burst Mode operation, constant frequency mode and continuous inductor current mode or regulate a secondary winding.

ABSOLUTE MAXIMUM RATINGS

Input Supply Voltage (VIN) .........................30V to –0.3V

Top Side Driver Voltages

(BOOST1, BOOST2) ................................... 36V to –0.3V

Switch Voltage (SW1, SW2) ......................... 30V to –5V

INTVCC, EXTVCC, RUN/SS1, RUN/SS2, (BOOST1-SW1),

(BOOST2-SW2), PGOOD .............................. 7V to –0.3V

SENSE1+, SENSE2+, SENSE1–, SENSE2– Voltages .........................(1.1)INTVCC to –0.3V FREQSET, STBYMD, FCB Voltage ......... INTVCC to –0.3V ITH1, ITH2, VOSENSE1, VO

SENSE2 Voltages ... 2.7V to –0.3V

Peak Output Current <10μs (TG1, TG2, BG1, BG2) .....3A

INTVCC Peak Output Current ................................. 40mA

Operating Temperature Range (Note 2).... –40°C to 85°C

Junction Temperature (Note 3) ............................. 125°C

Storage Temperature Range ................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec) .................. 300°C

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