Triple Output Synchronous Step-Down DC/DC Controller

The strong on-board gate drivers power all N-channel MOSFET stages and can produce output currents up to 20A per phase with output voltages ranging from 0.8V to 13.5V. Applications include point-of-load regulation in datacom, telecom, set-top boxes, basestations, and multifunction printers, where multiple voltage rails must deliver high power with low heat dissipation in a small solution size.

A constant-frequency current mode architecture allows a selectable fixed or phase-lockable (PLL) frequency from 250kHz to 750kHz. Power loss and supply noise are minimized by operating the three stages 120° out-of-phase. The LTC3853 can also be used in a 2+1 configuration, with output stages 1 and 2 180° out of phase. OPTI-LOOP® compensation allows for a wide range of output capacitance and ESR values, including all ceramic input and output capacitors. Output current sensing is accomplished by measuring the voltage drop across the output inductor (DCR) or by using an optional sense resistor. Current foldback limits MOSFET heat dissipation during short-circuit and overload conditions.

In addition, the LTC3853 has adjustable soft-start to control the turn-on time. Selectable Burst Mode® operation, pulse skipping or continuous inductor current modes are user controlled to optimize light load efficiency vs. output ripple. The LTC3853 features a precision 0.8V reference with an accuracy of ±1% over a -40°C to 125°C operating temperature range. With up to 98% duty cycle, the LTC3853 has a very low drop-out voltage, a useful feature for extending run times in battery-powered applications.