Due to superior light-load efficiency and high-bandwidth design capability, constant-on time (COT) control is preferred for multiphase buck regulators. For compensation design, single-phase model can be extended to multiphase only when there is no phase overlapping. Based on describing function method, this work introduces a general small-signal model for multiphase COT control applicable for both no-phase overlapping and phase overlapping regions. Also, this model is used to formulate compensation design guideline for achieving adequate phase margin for wide duty cycle operation with non-zero load line and zero-load line. Proposed model is verified with the SIMPLIS simulation and experiments.
