Modeling a Hysteretic Modulator's PFM and PWM Modes

摘要

In this paper, the describing function approach is used to extend the modeling of hysteretic mode control from the PWM mode to the PWM/PFM dual mode. A detailed circuit configuration of the PFM modulator and derivation of the model are introduced. Based on the derived model, a single zero transfer function is presented and several engineering approximations are applied to represent the dynamic characteristics of the PWM/PFM hysteretic modulator. A closed loop analysis is performed to assist the system designer with understanding the modulator.