A new current mode control for higher noise immunity and faster transient response in multi-phase operation

This paper presents a new current mode control using charge control concept to improve the performances of the constant on time control. These days, constant on time control is widely used in VR applications for its higher light load efficiency and higher bandwidth design capability. In this constant on time configuration, inductor current ripple based current mode control is very popular in today's industry because of its excellent small signal property with simple compensation network. The issue of this ripple based current mode control is that when the inductor current ripple becomes very small because of ripple cancellation effect in multiphase operation, control becomes very noise sensitive and create jittering at the output. Another issue in multiphase operation is - limited pulse overlapping capability at heavy load step up transient might create large undershoot at the output. In this paper, a new current mode constant on time control, based on charge control concept, is presented to improve the load step up transient performance in multiphase operation by achieving natural and linear pulse overlapping without adding any nonlinear control and to improve the noise immunity at ripple cancellation point without adding any external ramp into the system. Simulation and hardware test results in standard VR platform are also presented to verify the proposed concept.