Current estimation and remote temperature monitoring system for low power digitally controlled DC-DC SMPS

This paper describes a simple adaptive digital system that can accurately estimate steady-state inductor current and, at the same time, provide remote temperature monitoring of power switches in low-power digitally controlled dc-dc converters. The system is well-suited for on-chip implementation. It provides a solution for combining a digital controller, current estimator and remote temperature monitor on a single integrated circuit. To estimate the current and temperature, the estimator utilizes inherently available information about the duty ratio and performs auto-calibration through the utilization of a current sink. During regular converter operation, a known load current step is introduced and the inductor current and a dc resistance R_eq emulating converter losses are calculated from the resulting increase in the duty ratio control variable. Then, based on the obtained resistance value, the temperature of the switching components is found. The effectiveness of the estimator is demonstrated on a digitally-controlled 1.5 V, 15 W buck converter operating at 500 kHz switching frequency.