Step-down DC/DC Controller Rated at 20A

(Product News, 25 Aug 2008)

Linear Technology Corp.'s LTC3851 wide input range synchronous step-down switching regulator controller drives all N-channel power MOSFET stages and has coincident or ratiometric tracking. The 4V to 38V input range encompasses a wide variety of applications, including most intermediate bus voltages and battery chemistries. The strong on-board MOSFET gate drivers allow the use of high power external MOSFETs to produce output currents up to 20A with output voltages ranging from 0.8V to 5.5V, making the LTC3851 ideal for point-of-load requirements. Applications include automotive, industrial, medical, datacom and telecom systems, multifunction printers and set-top boxes.

A constant-frequency current mode architecture provides a selectable fixed or phase-lockable (PLL) frequency from 250kHz to 750kHz. OPTI-LOOP compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values, including all ceramic capacitors designs. Output current sensing is accomplished by measuring the voltage drop across the output inductor (DCR) or by using an optional sense resistor; also the current limit threshold voltage is programmable. Current foldback limits MOSFET heat dissipation during short-circuit and over-load conditions. In addition, the LTC3851 has adjustable soft-start to control the turn-on time and manage inrush current. Selectable Burst Mode operation, pulse skip mode or continuous current mode is user controlled to optimize light load efficiency vs. output ripple. The LTC3851 features a precision 0.8V reference with an accuracy of ±1 percent over a -40°C to 85°C operating temperature range. With up to 99 percent duty cycle, the LTC3851 has a very low drop-out voltage, a useful feature for extending run times in battery powered applications.

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