Subharmonic Analysis for Buck Converters With Constant On-Time Control and Ramp Compensation

This paper presents a new subharmonic analysis for buck converters with constant on-time control and ramp compensation. For constant on-time control, subharmonic oscillation can be eliminated by adding a compensation ramp with a fixed slope during the off time and a fixed level during the on time. Based on the inductor current information, the compensation ramp, and the charge variations of the output capacitor, the minimum amount of compensation ramp to avoid subharmonic is derived, and the effect of circuit propagation delay is quantified. A prototype of buck converter is built by using constant on-time control with ramp compensation. Experimental results demonstrate the detailed theoretical analysis.