Inductor DCR Current-Sense Calculator

DCR current sensing emerged in the 2000s as CPU voltage regulator module (VRM) designs pushed above 100 A load current, where I-squared-R loss in a 5-milliohm sense resistor (~5 W) became unacceptable. Intersil (now Renesas) and Linear Technology pioneered the matching-RC-network technique in controller ICs like the ISL6559 and LTC3731. By 2010 every multiphase CPU VRM and server buck converter used DCR sensing; the technique also moved into motor drives and battery management.

Enter inductor L, DCR (milliohms, from datasheet), sense cap C (typically 100 nF-1 µF), and load current for V_sense estimation. The tool solves R = L/(DCR·C) such that the RC time constant matches L/DCR — producing a capacitor voltage proportional to inductor current.

V_sense = I·DCR; pick the sense amp input range accordingly. For ±1% accuracy over temperature, add a thermistor voltage-divider for DCR compensation. Modern PWM controllers (ISL, TPS, MAX series) have built-in DCR sense networks with digital trim. Everything runs client-side.