Effect of Combined Output Capacitors for Stability of Buck Converters With Constant On-Time Control

Constant on-time control has been widely used for power supply controllers in industry due to its fast transient response. However, existing stability analysis in literatures can only explain conditions with single type of output capacitor and usually recommend high equivalent series resistance ( ESR) *Co for stable operation. This paper proposes a new stability analysis for constant on-time control with combined output capacitors, which are often used in practical applications. Based on time-domain analysis for the inductor current, the output voltage, and the output capacitor currents, it is revealed that higher ESR and higher capacitance values can deteriorate the stability in many conditions with combined output capacitors. Also, a simple loop compensation solution is provided to improve stability. Simulation and experimental results demonstrate the theoretical analysis.