2-Phase, 5-Bit VID, Current Mode, High Efficiency, Synchronous Step-Down Switching Regulator

The LTC1709-7 is a 2-phase, VID programmable, synchronous step-down switching regulator controller that drives two all N-channel external power MOSFET stages in a fixed frequency architecture. The 2-phase controller drives its two output stages out of phase at frequencies up to 300kHz to minimize the RMS ripple currents in both input and output capacitors. The 2-phase technique effectively multiplies the fundamental frequency by two, improving transient response while operating each channel at an optimum frequency for efficiency. Thermal design is also simplified.

An operating mode select pin (FCB) can be used to regulate a secondary winding or select among three modes including Burst Mode™ operation for highest efficiency. An internal differential amplifier provides true remote sensing of the regulated supply’s positive and negative output terminals as required in high current applications.

The RUN/SS pin provides soft-start and optional timed, short-circuit shutdown. Current foldback limits MOSFET dissipation during short-circuit conditions when the overcurrent latchoff is disabled. OPTI-LOOP compensation allows the transient response to be optimized for a wide range of output capacitors and ESR values.

Vout Range

VRM

LTC1709

1.3V to 3.5V

VRM8.4

LTC1709-7

0.925V to 2V

Mobile

LTC1709-8

1.3V to 3.5V

VRM8.4

LTC1709-85

1.05V to 1.825V

VRM8.5

LTC1709-9

1.1V to 1.85V

VRM9.0

Applications

* Mobile/Desktop Computers

* Internet Servers

* Large Memory Arrays

* DC Power Distribution Systems

* Output Stages Operate Antiphase Reducing Input Capacitance Requirements and Power Supply Induced Noise

* Dual Input Supply Capability for Load Sharing

* 5-Bit Mobile VID Code: VOUT = 0.925V to 2V

* Current Mode Control Ensures Current Sharing

* True Remote Sensing Differential Amplifier

* Power Good Output Indicator

* OPTI-LOOP™ Compensation Minimizes COUT

* Three Operational Modes: PWM, Burst and Cycle Skip