External ramp autotuning for current mode control of switching converters

An external ramp autotuning is proposed to optimize the dynamic performance of current-mode control. Conventionally, a fixed external ramp is chosen to compensate the worst-case of inductor current slope variation, while prior adaptive ramp compensation strategies cannot adaptively compensate the current slope variation by inductor tolerance and topology change. Therefore, using either approach, the overall performance suffers from over compensation, so system bandwidth is limited. This paper shows tuning external ramp slope to track the constant quality factor of double pole at half of switching frequency based on sensed slope of current feedback signal, so stable and wide bandwidth performance over all possible duty cycle variation, inductor tolerance, and topology change is achieved without suffering from worst-case design. Simple digital and analog implementations are proposed to realize the autotuning method. This method is applicable to digital or analog current-mode controllers with peak current mode, valley current mode, and average current mode operations. The effectiveness of the proposed method has been verified with simulation and experimental results.