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High Power Multiphase Step-Down DC/DC Controller Features Differential Remote Sensing, Active Voltage Positioning & Stage Shedding Technology

24th May 2010

Linear Technology (UK) Limited

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Datasheet

Linear Technology introduced the LTC3856, a two-phase single output high efficiency (up to 95%) synchronous step-down DC/DC controller with PolyPhase® operation, differential output voltage sensing and integrated phased-lock loop (PLL) synchronization. Up to 12 phases can be paralleled and clocked out of phase to minimize input and output filtering requirements for high current applications (up to 300A). The differential amplifier provides remote output voltage sensing of both the positive and negative terminals, enabling high accuracy regulation independent of IR losses in trace runs, vias and interconnects. Applications include high current ASIC and FPGA supplies, power distribution buses, high power audio amplifiers and network servers.

The LTC3856 operates with all N-channel MOSFETs from input voltages ranging from 4.5V to 38V and it can produce ±0.75% accurate output voltages from 0.6V to 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 current limit set point over a broad temperature range. The powerful onboard gate drivers minimize MOSFET switching losses and enable 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 LTC3856 ideal for high step-down ratio applications.

The LTC3856 incorporates an adjustable Stage Shedding™ technique to increase efficiency at light loads by eliminating gate charge and switching losses of one of its output stages. In addition, the LTC3856 can be configured for adjustable Burst Mode® operation to produce even higher efficiency at light loads. Its adaptive voltage positioning (AVP) minimizes the maximum transient voltage deviation during a load current step.

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, a power good output and external VCC control.