Online calibration of MOSFET on-state resistance for precise current sensing

An approach for online current sensing calibration is presented 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 online calibration approach, showing a significant improvement in accuracy over voltage sensing across the power MOSFET on-resistance.