Digital Hybrid Ripple-Based Constant On-Time Control for Voltage Regulator Modules

This paper presents a digital hybrid ripple-based constant on-time control scheme for voltage regulator modules (VRMs). Due to the sampling effects of the digital implementation, the stability issue becomes worse than the analog ripple-based control schemes, especially when the composite output capacitors are utilized. In order to stabilize the system and to fulfill the output impedance requirement of adaptive voltage positioning (AVP), a hybrid ramp compensation strategy, which includes the external ramp and the estimated current ramp, is proposed in this paper. No complicated compensators are required as the conventional voltage-mode control. The small-signal model of the proposed architecture is derived to provide the design guideline for the ramp compensation gains with different output capacitors. Besides, the oversampling effect of the output voltage by using analog-to-digital converters (ADCs) are also analyzed by using the presented model. Simulation and experimental results show that the proposed digital ripple-based control architecture can achieve fast load transient performance and to fulfill the AVP design requirements of single-phase VRMs.