A 12-to-1 Flying Capacitor Cross-Connected Buck Converter With Inserted D > 0.5 Control for Fast Transient Response Tingxu Hu, Student Member , IEEE

Abstract

This article presents a 12-to-1 flying capacitor cross- connected (CCC) converter with an inserted duty cycle ( D) > 0.5 control for fast transient response. As analyzed, CCC and double- step-down (DSD) converters have almost the same power loss and silicon area, while the CCC uses a much smaller input capacitance. Besides, with the proposed D > 0.5 control, the CCC achieves > 2× inductor current slew rate and thus a faster transient response, when compared with a conventional DSD con- verter. Subsequently, we use a primary–secondary synchronized hysteretic (SH) controller that further improves the transient response. We investigate the small-signal model to guide the controller’s design. Moreover, we propose a shared bootstrap circuit to save the silicon area. The prototype chip fabricated in a 0.18-µm HV-SOI process occupies a die area of 2.8 mm 2. The measured peak efficiency is 86.8% with a 12-V input, a 1.2-V output, and a 2-MHz switching frequency. With two 0.74-µH inductors and a 10.6- µF output capacitor, the measured undershoot is 110 mV with a 4-A load current step. The normalized undershoot is 0.73× the minimum undershoot that DSD can achieve.