Fast 2-Phase, No R Buck Controller with Output Tracking

The LTC3708 is a dual, 2-phase synchronous step-down switching regulator with output voltage up/down tracking capability. The IC allows either coincident or ratiometric tracking. Multiple LTC3708s can be daisy-chained in applications requiring more than two voltages to be tracked. Power supply sequencing is accomplished using an external soft-start timing capacitor.

The LTC3708 uses a constant on-time, valley current mode control architecture to deliver very low duty factors without requiring a sense resistor. Operating frequency is selected by an external resistor and is compensated for variations in input supply voltage. An internal phase-locked loop allows the IC to be synchronized to an external clock.

Fault protection is provided by an output overvoltage comparator and an optional short-circuit shutdown timer. The regulator current limit level is user programmable. A wide supply range allows voltages as high as 36V to be stepped down to 0.6V output.

Applications

* Notebook and Palmtop Computers, PDAs

* Digital Signal Processors

* Network Servers

* Very Low Duty Factor Operation (tON(MIN) < 85ns)

* No RSENSE™ Option for Maximum Efficiency

* Very Fast Transient Response

* Programmable Output Voltage Up/Down Tracking

* 2-Phase Operation Reduces Input Capacitance

* 0.6V ±1% Output Voltage Reference

* External Frequency Synchronization

* Monotonic Soft-Start

* On-board High Current MOSFET Drivers

* Wide VIN Range: Up to 36V

* Adjustable Cycle-by-Cycle Current Limit

* Instant Output Overvoltage Protection

* Optional Short-Circuit Shutdown Timer

* Power Good Output with 100µs Masking

* Available in 5mm × 5mm QFN Package