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Power/Alternative Energy??

DC/DC controller regulates pre-biased loads

Posted: 15 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:DC/DC controller? switch? regulator? capacitor?

Linear Technology Corp. has launched a highly efficient, triple-output, synchronous step-down switching regulator controller with coincident or ratiometric tracking that safely powers pre-biased loads. The LTC3853 targets point-of-load regulation in datacom, telecom, STBs, base stations, and multifunction printers, where multiple voltage rails must deliver high power with low heat dissipation in a compact size.

The 4.5V to 24V (28V max) input range has a wide variety of applications covering the most intermediate bus voltages. The 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.

A constant-frequency, current-mode architecture permits a selectable fixed or PLL frequency from 250KHz to 750KHz. Power loss and supply noise are reduced 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 equivalent series resistance values including all ceramic input and output capacitors.

The LTC3853 has a precision 0.8V reference with an accuracy of 1 percent from 40C to 125C operating temperature range. With up to 98 percent duty cycle, the LTC3853 has a very low drop-out voltage, a useful feature for extending runtimes in battery-powered applications.

Output current sensing is accomplished by measuring the voltage drop across the output inductor or by using an optional sense resistor. Current foldback limits MOSFET heat dissipation during short-circuit and overload conditions.

At the same time, the controller provides 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 is offered in a thermally enhanced 6mm x 6mm QFN-40 package.

-Gina Roos
eeProductCenter





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