Buck Circuit Design With Pseudo-Constant Frequency and Constant On-Time for High Current Point-of-Load Regulation

Abstract

This paper introduces an accurate frequency regulation method based on a constant on-time (COT) buck regulator designed for point-of-load (POL) regulation with a fast load transient requirement and wide load range. Traditional COT regulators suffer from frequency shift due to load variations. The proposed frequency adjustment circuit helps the COT control engine to reach its target frequency of operation by adjusting the on-time pulse under varying conditions. This circuit includes a phase detector and a voltage-to-current converter block. The phase error between the target clock signal and the PWM is directly used to adjust the width of the on-time pulse. This will fine-tune the bandwidth of the frequency regulation loop, which can help to improve the transient performance of the COT as well. The fabricated chip has been tested under 20A/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> load transient speed with a 10A load step condition. The measured silicon performance shows that the error of the switching frequency is less than 0.16% in the 400kHz to 1MHz range during steady-state operation.