Sub-milliOhm DCR-sensing multiphase step-down DC/DC controller

January 23, 2014 // By Graham Prophet
LTC3875 is a dual output current-mode synchronous step-down DC/DC controller that enables the use of very low DC-resistance (DCR) power inductors by using a novel DCR sensing architecture that enhances the signal-to-noise ratio of the current sense signal.

Power inductor DCR as low as 0.2 milliOhms (m Ω) can be used without a sense resistor to maximise converter efficiency and increase power density. This DCR sensing technique dramatically reduces the switching jitter normally associated with low-DCR sensing applications.

LTC3875 operates over an input voltage range of 4.5V to 38V and produces a fixed output voltage from 0.6V to 3.5V with ±0.5% accuracy from -40°C to 125°C. Dual onboard differential amplifiers provide true remote output voltage sensing of both output voltages. Up to 12 phases can be paralleled and clocked out-of-phase to minimise input and output filtering. When both outputs are paralleled, the LTC3875 maintains less than ±5% current mismatch between phases, making it suitable for very high current requirements up to 360A. Precise programmable current sense limits and DCR temperature compensation limit the maximum output current precisely over temperature. Applications include high current power distribution, redundant (n+1) supplies, industrial systems, processor and ASIC power.

The LTC3875 has a selectable fixed operating frequency from 250 kHz to 720 kHz or it can be synchronised to an external clock. 1.1- Ω onboard all-N-channel gate drivers minimise MOSFET switching losses. Its adjustable current limit can be configured for very low sense voltages from 10 to 30 mV to minimise power loss. The second channel features a fast transient circuit that improves the load-step-up transient by up to 30% . Additional features include adjustable soft-start or tracking, foldback current limit, short-circuit soft recovery, output overvoltage protection and a power-good output voltage monitor.

The LTC3875 is available in a 40-lead 6 x 6 mm QFN package for $3.47 (1000).

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