Analysis of the effect of modulation delays on the size of the output capacitor

Constant frequency (PWM), constant on-time (COT) and constant off-time modulations exhibit inherent delays where the controller is unable to respond instantaneously. These delays can increase the required size of the output capacitor to meet dynamic requirements in applications with high demanding load such as the supply of microprocessors. This paper analyzes the minimum required output filter (output inductor and output capacitor) to meet a given specification and quantifies the effect that different modulations have in the minimum size of the output capacitor. The paper also shows a novel technique to mitigate the delays of the modulations by means of synchronizing the load step with the clock of the modulation. This technique is applicable to most of controllers as it only acts on the modulator.