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Dual-output DC/DC controller offers up to 12 phases

Posted: 13 Nov 2009 ?? ?Print Version ?Bookmark and Share

Keywords:DC/DC controller? amplifier? FPGA?

Linear Technology Corp. unveils a dual-output synchronous step-down DC/DC controller with multiphase operation, differential output voltage sensing and integrated PLL synchronization. The LTC3855 claims 95 percent efficiency, offering up to 12 phases that can be paralleled and clocked out of phase to minimize input and output filtering requirements for current applications up to 200A.

The differential amplifier provides true remote output voltage sensing of both the positive and negative terminals, enabling high accuracy regulation where IR losses occur through vias, trace runs and interconnects. Applications include high current ASIC and FPGA supplies, power distribution buses, high power audio amplifiers and network servers.

The LTC3855 operates with all n-channel MOSFETs from input voltages ranging from 4.5V to 38V, and it can produce >0.75 percent accurate output voltages from 0.6V to 12.5V. The output current is sensed by monitoring the voltage drop across the output inductor (DCR) or by using a sense resistor. Programmable DCR temperature compensation maintains an accurate and constant over current limit over a broad temperature range. The onboard 1.1? gate driver minimizes MOSFET switching losses and allows the use of multiple MOSFETs connected in parallel. A fixed operating frequency can be programmed from 250KHz to 770KHz or can be synchronized to an external clock with its internal PLL. The device's minimum on-time of just 90ns makes the LTC3855 suited for high step-down ratio applications.

Tracking and sequencing functions allow the optimization of power-up and power-down of multiple power supplies. Additional features include current mode control, an onboard LDO for IC power, programmable soft start, two power good signals and external VCC control.

The LTC3855 is available in 38-lead SSOP or 40-lead 6mm x 6mm QFN packages. The LTC3855E operates from -40C to 85C, with the 1000-piece price starting at $3.18. The LTC3855I Industrial grade version operates from -40C to 125C, with a 1,000-piece price starting at $3.59 each. Both versions are available from stock.

For application notes on DC/DC controllers click here.

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