A novel ripple-based constant on-time control with virtual inductor current ripple for Buck converter with ceramic output capacitors

Ripple-based constant on-time (RBCOT) control has found applications because of its fast load transient response, small component count, and good light-load efficiency. However, this control scheme often encounters instability issue of subharmonic oscillation when ceramic capacitors are used for converter output filter capacitors. In the paper, a novel RBCOT control with virtual inductor current ripple was proposed to alleviate this problem. The novel control scheme improves system stability of RBCOT control without adding extra pins and converter components in IC implementation. Thus resulting in less component count and controller cost. Describing function method was used to derive the model and stability criterion of the proposed scheme, including the effect of delay-time. The scheme was implemented in an IC. Simulation and experimental results also confirm the proposed concept and the accuracy of the stability criterion developed.