Load Transient Response Analysis of Constant On-Time DC-DC Converters Using a State-Variables Approach

In the design of constant-on-time buck converters, prediction of the onset of subharmonics, at steady-state working conditions, and prediction of the saturation of the controller, i.e., the occurrence of at least one switching cycle at minimum off-time, after a dynamic step variation of the load are relevant aspects. By starting from the design parameters of a constant-on-time buck converter and grounding on a state-variables approach, we consider these aspects and develop a reliable and efficient approach to determine both limits. The proposed approach, despite having rigorous mathematical basis, is sufficiently simple. Thus it can be easily applied to predict results in designing constant-on time buck converters. The accuracy and effectiveness of the proposed approach is tested versus experimental results. This article is accompanied by a MATLAB live script that allows the reader to reproduce the proposed results and create new case studies.