A 12-to-1 Flying Capacitor Cross-Connected Buck Converter With Inserted <i>D</i> > 0.5 Control for Fast Transient Response
Tingxu Hu, Mo Huang, Rui P. Martins, Yan Lü
Abstract
This article presents a 12-to-1 flying capacitor cross-connected (CCC) converter with an inserted duty cycle ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D) > $ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D > $ </tex-math></inline-formula> 0.5 control, the CCC achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$>\,\,2\times $ </tex-math></inline-formula> inductor current slew rate and thus a faster transient response, when compared with a conventional DSD converter. 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- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> HV-SOI process occupies a die area of 2.8 mm2. 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- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{H}$ </tex-math></inline-formula> inductors and a 10.6- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{F}$ </tex-math></inline-formula> output capacitor, the measured undershoot is 110 mV with a 4-A load current step. The normalized undershoot is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.73\times $ </tex-math></inline-formula> the minimum undershoot that DSD can achieve.