Digital Synthetic Ripple Modulator for point-of-load converters

Hysteretic modulators exhibit superior dynamic performance and without sacrificing the transient response they help to reduce the number of output capacitors. Due to tight regulation requirements modern point-of-load converters have very small output ripple. This small output ripple fails to generate a suitable piece-wise linear modulation waveform for the hysteretic comparator. This paper presents a fully digital Synthetic Ripple Modulator (SRM) comprising of a hysteretic comparator, a ripple synthesizer, and a voltage error amplifier for tight output voltage regulation. The ripple synthesizer realizes a high-quality low-cost current sensors by creating a piece-wise linear synthetic ripple using sensed converter voltages. This artificial ripple is then added to the output voltage and fed as a carrier to the hysteretic comparator. This improves the large signal dynamics of the converter, especially in low voltage application. Analysis and experimental results on a 2 V/10 A, 20 W single phase prototype are presented to verify the operation of the proposed digital SRM.