Three-phase step-down DC/DC controller targets high current rails
May 13, 2010 // Paul Buckley
Linear Technology Corporation has introduced a three-phase single output high efficiency (up to 95 percent) synchronous step-down DC/DC controller with PolyPhase operation, differential output voltage sensing and integrated phased-lock loop (PLL) clock synchronization.
Up to six phases can be paralleled and clocked out of phase to minimize input and output filtering requirements for high current applications (up to 150 A). The differential amplifier provides true 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 LTC3829 operates with all N-channel MOSFETs from input voltages ranging from 4.5 V to 38 V, and it can produce ±0.75 percent accurate output voltages from 0.6 V to 5 V. 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 allows the use of multiple MOSFETs connected in parallel. A fixed operating frequency can be programmed from 250 kHz to 770 kHz or can be synchronized to an external clock with its internal PLL. The device's minimum on time of just 90ns makes the LTC3829 ideal for high step-down ratio applications.
The LTC3829 incorporates an adjustable Stage Shedding technique to increase light load efficiency by eliminating the gate charge and switching losses of two of its output stages. In addition, the LTC3829 can be configured for adjustable Burst Mode operation, producing even higher efficiency at light loads. An optional non-linear control mode improves load step transient response and adaptive voltage positioning (AVP) minimizes the maximum transient voltage deviation during a step-load.
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.
Availability and Pricing
The LTC3829 is available in thermally enhanced 38-lead TSSOP or 38-lead 5 mm x 7 mm QFN packages and operates over a -40 to 125 degrees C operating junction temperature range with the 1000-piece price starting at 3.71 US Dollars each. Both versions are available from stock.
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