High precision load current sensing using on-line calibration of trace resistance in VRM applications

A method for the on-line calibration of a circuit board trace resistance at the output of a buck converter is described. The input current is measured with a precision resistor and processed to obtain a DC reference for the output current. The voltage drop across a trace resistance at the output is amplified with a gain that is adaptively adjusted to match the DC reference. This method is applied to obtain an accurate and high-bandwidth measurement of the load current in the modern microprocessor voltage regulator application (VRM), thus enabling an accurate DC load-line regulation as well as a fast transient response. Experimental results show an accuracy well within the tolerance band of this application, and exceeding all other popular methods.