Digital V2 control with fast-acting capacitor current estimator

A digital hybrid ramp compensation method with output capacitor current ramp estimator and external ramp for digital V² control is proposed to solve the stability issues in low-ESR output capacitor application of buck converters. Since capacitor current is in derivative relation with output voltage, the proposed method has faster transient response and simpler structure than digital inductor current estimation. Besides, proposed estimation technique solves ramp distortion issue of prior analog or digital capacitor current estimators considering the ESR and ESL of output capacitor. The small-signal model is derived by describing function to understand the dynamic of the current estimator and provides stability criteria to design the current feedback gain and external ramp slope in proposed structure. The effectiveness of the proposed control structure and the current ramp estimator has been verified with simulation and experimental results.