A Novel Ultrafast Transient Constant on-Time Buck Converter for Multiphase Operation

Constant on-time control (COT) has been widely adopted in buck converters because of its simplicity, fast transient response, and high light-load efficiency. However, the increasing power demands of CPUs and AI/ML engines is pushing voltage regulators to support higher output currents, which typically requires the use of multiphase operation. However, since most high-performance COT schemes utilize ripple as a control variable, the ripple cancellation point in multiphase designs imposes difficult stability concerns, limiting performance, and robustness. In this article, a novel ultrafast transient COT (UFTCOT) control scheme is proposed to enable fast and robust operation even in multiphase converters. The small-signal models of the proposed control scheme are derived based on a describing function technique, whose theoretical results are compared, along with simulation and measurement results, to contrast the proposed UFTCOT technique to exiting approaches.