A Cascaded Hybrid Switched-Capacitor DC–DC Converter Capable of Fast Self Startup for USB

Abstract

Hybrid switched-capacitor (SC) dc–dc converters show promise in applications that require high conversion ratios and small physical size. However, the problem of flying capacitor voltage imbalance, especially during transients, remains a major challenge that limits the adoption of such converters. This article presents a highly integrated hybrid switched-capacitor (SC) converter for universal serial bus (USB) powered applica- tions, featuring fast balancing dynamics. The topology consists of two cascaded stages to increase the conversion ratio. The output voltage regulation and flying capacitor active balance are both achieved by modified ripple injection control (MRIC), with an additional phase skipping technique further improving the transient response during startup. Fabricated in 0.18 µm complementary metal-oxide-semiconductor (CMOS) technology, the converter prototype has a peak efficiency of 96.9% for 5:1.2 V conversion. Safe startup can be achieved with the input voltage rising from 0 to 5 V within 8 µs (0.62 V/ µss l e wr a t e ) .