Analysis of multi-phase hybrid ripple-based adaptive on-time control for voltage regulator modules

This paper presents the multi-phase hybrid ripple-based adaptive on-time control architecture for VRMs. Due to the ripple cancellation effects with multi-phase operations, ripple-based control may suffer from large jitter issues and instability issues when applying to VRMs with ceramic output capacitors. By utilizing the hybrid ripple concept, both inductor current ripple and compensated external ramp are fed back to the modulator to reduce jitter and improve stability. However, the system becomes more complicated with two different ramp compensations. A small-signal model is derived based on the describing function approach to analyze the proposed control architecture and to provide the design guideline for determining the external ramp compensations based on different load-line requirements. Moreover, a feedforward controller is presented to improve the reference tracking performance of the conventional ripple-based control. Both simulation and experimental results are given to show the effectiveness of the proposed control architecture for VRMs, and to show the fast load transient and fast reference tracking characteristic of the hybrid ripple-based control scheme.