4-output multiphase step-down DC/DC controller: up to 260A

February 09, 2016 // By Graham Prophet
LTC7851/-1 is a quad output multiphase synchronous step-down DC/DC controller with accurate current sharing between phases and differential output voltage sensing. Up to eight phases (with two ICs) can be paralleled and can be clocked out-of-phase to minimise input and output filtering for very high current requirements up to 260A.

This controller works in conjunction with external power train devices such as DrMOS and power blocks as well as discrete N-channel MOSFETs and associated gate drivers, enabling flexible design configurations. Applications include power distribution and industrial systems, FPGA, DSP, processor and ASIC supplies.

An internal current share loop equalises current between phases when paralleled, enabling accurate current sharing between phases across multiple ICs, both in steady state and during a transient event. It operates with a VCC supply voltage from 3V to 5.5V, is designed for step-down conversion from an input voltage from 3V to 27V and produces one to four independent output voltages ranging from 0.6V to 5V. The device’s voltage mode control architecture allows for a selectable fixed operating frequency from 250 kHz to 2.25 MHz or it can be synchronised to an external clock over the same range. The output current is sensed by monitoring the voltage drop across the output inductor (DCR) for maximum efficiency or by using a low value sense resistor. The onboard differential amplifiers provide true remote output voltage sensing for all outputs of both VOUT and ground terminals for high accuracy regulation.

The LTC7851-1 is similar to the LTC7851, but with a lower current sense amplifier gain, for power train applications using DrMOS with internal current sense capability. Additional features for each phase include current monitoring, adjustable current limit, programmable soft- start or tracking, and a power-good signal. It maintains ±0.75% reference voltage accuracy over an operating temperature range of -20°C to 85°C.

The LTC7851/-1 is housed in a 58-lead 5mm x 9mm QFN package and is priced from $4.27 (1000).

Linear Technology; visit www.linear.com/product/LTC7851