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 low-ESR decoupling capacitors are used as the output filter. 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. The small-signal model of the proposed architecture is derived to provide the design guideline for the ramp compensation gains and the number of output and decoupling capacitors. Besides, only low sampling-rate Analog-to-Digital Converters (ADCs) are required to sample the input voltage, the output voltage, and the average current making the proposed architecture compatible with the cost/complexity constraints of VRM applications. Simulation and experimental results show that the ripple-based control can achieve high-bandwidth performance, and the proposed digital control architecture can fulfill the AVP design requirements of single-phase VRMs.