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 near-soft 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- μm CMOS, occupies a core area of 0.86 mm 2 . It achieves a 93.5% peak efficiency when the CR is 4.5, with two 3.3- μH inductors (3010 package), two 0.47- μF C F s, and a 2-MHz switching frequency.