A Novel Adaptive-Ramp Ripple-Based Constant On-Time Buck Converter for Stability and Transient Optimization in Wide Operation Range

The fixed-ramp ripple-based constant on-time (RBCOT) control scheme for buck converters has recently been adopted in many dc–dc conversion applications for its simplicity and high light-load efficiency. However, it cannot overcome the problems with feedback instability and excessive load transient response when the converter is required to cover wide working conditions of input voltage, output voltage, and switching frequency in the application of power management integrated circuit (PMIC). In this paper, an adaptive-ramp RBCOT scheme is proposed to solve such a problem. The control law is derived from theoretical analysis of small-signal models. A simple analog circuitry, which can be easily integrated into an integrated circuit, is proposed to achieve invariant Q factor (or Q value, quality factor) under different working conditions. Simulations and experiments were conducted to verify the proposed concept.

I. Introduction

In the past several years, ripple-based constant on-time (RBCOT) control scheme has been adopted in many dc–dc conversion applications due to their simplicity, low cost, fast load transient response, and high conversion efficiency under the light-load conditions without sacrificing its heavy-load efficiency. Due to the omission of the output dc regulation circuit, RBCOT scheme cannot meet the regulation precision needed for V-Core applications. However, it is well suited for non-V-Core (non-CPU core power) applications, such as input–output (I/O), phase-locked loop (PLL), and memory units, in which the requirements for the voltage precision and the current level are not as stringent. Recently, there have been research and development efforts to develop a dc converter based on the RBCOT buck configuration for low-end power management integrated circuit (PMIC) applications.