The analysis of multi-phase current feedforward type-III constant on-time control with ultrafast load transient response for voltage regulator modules

This paper presents a new method of addressing the constant on time and minimal off time limitation of widely used COT variable frequency control. This is done by means of estimated capacitor current feedforward method. Ultrafast transient response is achieved with a new COT controller reacting much faster to output caps charge and discharge currents following a load transient step. A new output caps current estimator circuit is presented that accurately models a complex output filter network, including effective series inductance. System frequency response with combined output cap current estimator circuit and a type-II error amplifier shows a voltage mode type-III compensator. New compensator enables higher BW with sufficient phase margin limits. Dynamic performance of 4 phase, 3MHz and 16A load step at 3uSec slew rate show superior transient response in both voltage deviation and recovery time. Integrated controller is implemented in a 0.18μm Tower Jazz process. ASIC performance closely matches target design specs.