Pseudo-Constant Switching Frequency in On-Time Controlled Buck Converter with Predicting Correction Techniques

Abstract

The predicting correction technique (PCT) is proposed to achieve an adaptive on-time control for ripple-based buck converters. The switching frequency f(SW) variation is suppressed when the PCT technique considers complete parasitic resistances of the components and devices. Even without extra clock-controlled circuits and current sensing circuits, the buck converter operates with a nearly constant f(SW) over a wide load range. Parasitic resistances almost cause no influence and restriction on f(SW). Only input voltage is used to predict the adaptive on-time. Measurement results show only 0.32% in Delta f(SW) / f(SW) and 5.7 kHz/A in Delta f(SW) / Delta I-LOAD in case of 1.4 A load current change and f(SW) is 2.5 MHz. Consequently, a pseudo-constant f(SW) with well-defined noise spectrum strongly benefits the solution of electromagnetic interference (EMI) for system-on-a-chip (SoC) applications.