A Voltage Ripple Compensation Method for Constant On-Time Buck Converter

Abstract

Subharmonic oscillation stands as a critical concern in the context of ripple-based constant-on-time (COT) controllers. While this issue can be mitigated through the application of the virtual inductor current (VIC) technique, it comes at the cost of load transient response. To achieve both high stability and rapid transient response, this paper introduces an Output Capacitor Voltage Ripple Compensation (VRC) technique. This technique minimizes the phase delay attributed to output capacitance by introducing a virtual output ripple ( $\text{V}_{\mathrm {VOR}})$ inversely related to the feedback voltage. The VVOR serves to expedite the load transient response by counteracting the additional virtual inductor current injection during load transients. Utilizing a $0.13\mu \text{m}$ BCD technology, a synchronous buck converter is integrated with the proposed VRC-COT controller, showcasing exceptional stability across a load current range of 0 to 8A, even when equipped with a 30% $88\mu \text{F}$ ceramic output capacitor. Additionally, the load transient response exhibits reduced overshoot and undershoot, measuring at 120mV and 130mV, respectively, in response to load steps from 0A to 8A within a $10\mu \text{S}$ timeframe.

Keywords

• Constant on-time (COT)
• ripple-based control
• voltage ripple compensation (VRC)
• equivalent series resistor (ESR)
• subharmonic oscillation