DC-DC Controller’s DCR Architecture Enhances Current-Sense SNR

The dc-resistance (DCR) sensing architecture implemented in Linear Technology’s LTC3875 dual-output current-mode synchronous step-down dc-dc controller helps improve a current-sense signal’s signal-to-noise ratio (SNR). The controller enables the use of very low DCR power inductors. Power-inductor DCR down to 0.2 mΩ can be used without a sense resistor to maximize converter efficiency and increase power density. With the new DCR sensing scheme, switching jitter associated with low DCR sensing applications reduces significantly. Input voltage ranges from 4.5 to 38 V, while fixed output voltage ranges from 0.6 to 3.5 V with ±0.5% accuracy from −40 to 125°C. Dual onboard differential amplifiers offer true remote output-voltage sensing of both output voltages. Up to 12 phases can be paralleled and clocked out-of-phase to minimize input and output filtering. Paralleled outputs maintain less than ±5% current mismatch between phases. Fixed operating frequency is selectable from 250 to 720 kHz, or it can be synchronized to an external clock. Onboard 1.1-Ω N-channel gate drivers reduce MOSFET switching losses. To minimize power loss, the controller’s adjustable current limit is configurable for sense voltages from 10 to 30 mV. The LTC3875 comes in a 40-lead, 6- by 6-mm QFN package.

LINEAR TECHNOLOGY CORP.