Autotuning techniques for digitally-controlled point-of-load converters with wide range of capacitive loads

This paper addresses auto-tuning of digital controllers for point-of-load (POL) switching converters with wide range of capacitive loads. Two auto-tuning methods are considered with particular attention given to robustness and feasibility. The first method is derived from the well known relay-feedback autotuning technique, where specific frequencies are excited to gain information on the power stage. In the second, system-identification based method, compensator parameters are computed based on on-line identification of the power stage frequency response. The tuning techniques proposed in this paper have been specifically developed to handle wide capacitance and ESR range, and important extensions of the basic algorithms are implemented in order to face practical issues such as limit cycling conditions, output voltage tolerance specification, closed-loop bandwidth maximization and phase margin constraints. Simulation and experimental results on a 12-to-1.5 V, 9 A, 200 kHz POL converter are provided to show the effectiveness and to compare the considered techniques.