A 2.5MHz, 97%-accuracy on-chip current sensor with dynamically-biased shunt feedback for current-mode switching dc-dc converters

A 2.5MHz, 97%-accuracy on-chip current sensor for current-mode switching dc-dc converters is presented in this paper. By employing dynamically-biased shunt feedback, the non-dominant pole of the current sensor is pushed to higher frequencies, thereby improving the speed of the current sensor with low quiescent current consumption. Additionally, a feed-forward gain stage in the proposed current sensor increases the dc loop-gain magnitude and thus improves the accuracy of the current sensing. The proposed current sensor for the buck converter is designed using a standard 0.35 mu m CMOS process. Results show that the proposed sensor achieves at least 97% sensing accuracy and <30ns settling time by consuming the quiescent current of 43 mu A. The sensor allows the current-mode buck converter to operate at switching frequencies up to 2.5MHz with a duty cycle down to 0.2.