A 2-Level Buck Converter Using Adaptive ON/OFF-Time Control for Frequency-Stable Operation

Abstract

This paper presents an adaptive ON/OFF-time (AOOT) control technique for a 2-level buck converter designed in a 180-nm BCD technology. Conventional adaptive on-time (AOT) control provides a simple comparator-based structure; however, its fixed on-time operation inherently results in switching-frequency variation and ripple-dependent behavior, which can lead to sub-harmonic oscillation under wide operating conditions. The proposed AOOT scheme adaptively generates both ON- and OFF-time according to the input and output conditions, thereby enabling direct regulation of the switching period and reducing ripple-dependent instability associated with conventional AOT control under the simulated operating conditions, without requiring a complex compensation network. A 1-MHz buck converter is evaluated in simulation with a 2.5-V input, supporting a wide output voltage range from 0.5 to 2.0 V and a maximum load current of 2.5 A (5-W output power). Simulation results demonstrate that the proposed AOOT control maintains a near-target 1-MHz switching period under the representative simulated load and output voltage conditions, while achieving predictable steady state operation. The proposed AOOT adaptively generates both ON- and OFF-time according to operating conditions, enabling direct regulation of the switching period while reducing the dependence on output-ripple-based retriggering without high order compensation or ripple-injection circuits.