Dynamic PWM Ramp Signal to Improve Load Transient in DCM and Mode Hoping Operation

Abstract

Demanding high power applications, such as fast processors, and pulsed loads are requiring new levels of performance from dc/dc converters. The requirement of high slew rate of load current with minimal output voltage deviation is challenging. In case of load transient in CCM operation, the duty ratio is almost constant over the load current range, it slightly changes to compensate the extra losses and keep output voltage regulation. While in DCM and mode hoping operation, duty ratio varies significantly in case of load transient, the compensator is required to update the error signal, consequently the duty ratio, as load current varies. Since it takes longer time for the compensator to reach the steady state in cases of large duty cycle variation (DCM operation), the output voltage deviation during load transient is drastically increased when operating in DCM compared to CCM operation. Proposed is a control method, that dynamically modulate the PWM ramp signal peak, consequently modulate the PWM modulator gain, to minimize the required error signal change during load transient, so that the compensator reach steady state faster. Therefore, lower output voltage deviation during load transient can be achieved. Principle of operation, analyses, and experimental results are presented, revealing significant load transient improvement.