A Hybrid Boost Converter With Cross-Connected Flying Capacitors

This article presents a monolithic hybrid boost converter suitable for a high conversion ratio (CR). It uses two inductors, two cross-connected flying capacitors (C(F)s), and six power switches, allowing a two-phase operation and C(F)s nearsoft charging. With the internal voltages halved by the C(F)s, the inductor current ripple and voltage stress of the switches decrease, thus allowing a reduction in both power loss and silicon area. In addition, the cross-connected C(F)s double the pulsewidth of the control signals, thereby allowing a higher switching frequency even under a very high CR. Moreover, this design shares the large bootstrap capacitors of the high-side NMOS switches and also eliminates the need for an additional bootstrap voltage generation for the stacked NMOS switches, enabling an area-efficient full integration of the bootstrap capacitors. The converter, fabricated in 0.35-mu m CMOS, occupies a core area of 0.86 mm2. It achieves a 93.5% peak efficiency when the CR is 4.5, with two 3.3-mu H inductors (3010 package), two 0.47-mu F C(F)s, and a 2-MHz switching frequency.