On-line calibration of lossless current sensing

In this paper, we describe a lossless current sensing method with on-line calibration where an auxiliary switch and a precision sense resistor are connected in parallel with a main power switch to achieve accuracy comparable to the sense resistor method, together with the advantage of essentially no additional power loss. The proposed current-sensing circuit and the calibration methods are particularly well suited for digital controller implementations where the required control and calibration functions can be easily accomplished. Experimental results with a digitally controlled 1.5 V, 15 A synchronous buck converter demonstrate functionality of the on-line calibration approach, showing a significant improvement in accuracy over voltage sensing across the power MOSFET on-resistance.