Small-Signal Modeling of Multiphase V2 Constant On-Time Control with Phase Overlapping

Multiphase V (2) constant-on time control (COT) based on pulse distribution method is increasingly used in voltage regulators for CPUs and GPUs because of its good light-load efficiency, fast transient response, and simple structure. When the duty cycle of an N phase V (2) COT controlled buck exceeds 1/N, the output voltage exhibits variable on-time and off-time modulation from a small-signal perspective. Hence, single-phase V (2) COT control models cannot be extended to the multiphase V (2) control in the phase overlapping regions (or when D > 1/N). To address this issue, this work presents a general small-signal model of multiphase V (2) COT control architectures for the whole duty cycle range based on describing function method. The proposed models for multiphase V (2) COT control architectures are verified using SIMPLIS simulation and experimental results from a twelve phase V (2) COT controlled buck platform.