A lossless, accurate, self-calibrating current-sensing technique for DC-DC converters

High-performance, state-of-the-art applications demand smart power supplies to be adaptive, power efficient, and reliably accurate, which is why monitoring inductor current flow in a lossless fashion is not only desirable but also critical for protection and feedback control. Filter-based lossless current-sensing technique use a tuned filter across the inductor to estimate current flow, and its accuracy is dependent on the inductance and equivalent series resistance (ESR) of the device. Because of process-related tolerances, errors as high as ±28% are reported, even when the nominal inductor value is known, which is not the case for the IC designer, whose errors will then grossly exceed this value. A technique is proposed to boost the accuracy of these current-sensing filters by automatically adjusting their bandwidth and gain via phase and gain feedback control loops. The proposed scheme essentially measures the inductance and ESR values during startup and power-on reset events. Because the filter is automatically tuned to the inductor, the current during normal operation can be measured accurately by simply sensing the voltage across the inductor. A PCB prototype implementation of the proposed technique achieved overall DC and AC gain errors of 2.3% and 5% at full load, respectively, when lossless, state-of-the-art schemes achieve 20-40% error.