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Small two-phase DC/DC controllers feature 95% efficiency

Posted: 09 Jul 2007 ?? ?Print Version ?Bookmark and Share

Keywords:step-down switching regulator? DC/DC converter? ceramic capacitors?


Linear Technology Corp. has launched LTC3850, a 95-percent efficient, dual-output synchronous step-down switching regulator controller that drives all N-channel power MOSFET stages with coincident or ratiometric tracking. The 4-24V input range encompasses various applications including most intermediate bus voltages and battery chemistries. The strong on-board driver allows the use of high power external MOSFETs to produce output currents up to 20A with output voltages ranging from 0.8V to 5.5V. Applications include notebook and tablet PCs, portable instruments, datacom, telecom, STBs, basestations and multifunction printers where a step-down DC/DC converter must deliver high power with low heat dissipation in a small solution size.

A constant-frequency current mode architecture allows a selectable fixed or PLL frequency from 250kHz to 780kHz. Power loss and supply noise are minimized by operating both stages 180 out-of-phase. OPTI-LOOP compensation allows the transient response to be optimized over different output capacitance and ESR values, including all ceramic I/O 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 conditions.

In addition, LTC3850 has adjustable soft-start to control the turn-on time. Selectable Burst Mode operation, pulse skipping mode or continuous inductor current mode is user controlled to optimize light load efficiency vs. output ripple. LTC3850 features a precision 0.8V reference with an accuracy of 1 percent over a -40C to 85C operating temperature range. With up to 97 percent duty cycle, LTC3850 has a very low drop-out voltage, a useful feature for extending run times in battery-powered applications.

LTC3850 is offered in a thermally enhanced 4-by-4mm QFN-28 and SSOP-28 packages. Pricing for 1,000-piece quantities begins at $2.40 each.

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