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Step-down controller drives standard logic level from low-voltage supply

November 02, 2010 | Christoph Hammerschmidt | 222901177
Step-down controller drives standard logic level from low-voltage supply From a supply voltage of just 3.3V, Linear Technology's LTC3852 synchronous step-down DC/DC controller generates the supply voltage for low RDS(ON) and standard logic-level power MOSFETs. Since the LTC3852's internal charge pump and DC/DC controller are independent, the charge pump output can provide 5V to power the internal gate drivers, and the DC/DC converter power stage can draw power from another source with a voltage of up to 38V.

Output currents up to 25A can be supplied over an output voltage range from 0.8V to 99% of VIN (2.7V-5.5V), making the LTC3852 ideal for 3.3V-powered point-of-load applications. A constant-frequency current-mode architecture allows a selectable fixed or phase-lockable (PLL) frequency from 250kHz to 750kHz . Selectable Burst Mode® operation, pulse skip or forced continuous mode is user controlled to optimize light load efficiency. OPTI-LOOP® compensation allows the transient response to be optimized over 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) for highest efficiency, or by using an optional sense resistor in series with the inductor for highest accuracy. Current foldback limits MOSFET heat dissipation during short-circuit and overload conditions.

In addition, the LTC3852 has adjustable soft-start or tracking to control the turn-on characteristics of the supply, and features a precision 0.8V reference with an accuracy of ±1.25% over a -40°C to 125°C operating temperature range. With a maximum duty cycle of 99%, the LTC3852 has a very low dropout voltage, a useful feature for extending run times in battery-powered applications.

The LTC3852 is available in a thermally enhanced 3mm x 5mm QFN-24 package. The 1000-piece price starts at $1.95 and is available from stock. For more information, visit

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