A stable mode-transition technique for a digitally controlled non-inverting buck-boost DC-DC Converter

The propagation delay of a comparator and dead time causes the duty-discontinuity region near the boundary of the step-down and step-up regions in a non-inverting buck-boost (NIBB) converter. The duty-discontinuity region leads to an unstable output voltage and an unpredictable output voltage ripple, which might cause the entire power system to shut down. In this paper, a mode-transition technique called duty-lock control is proposed for a digitally controlled NIBB converter. It locks the duty cycle and eliminates the error between the output voltage and the reference signal by using a proposed fixed reference scheme that ensures the stability of the digital controller and output voltage. The experimental results that were applied to a field-programmable gate array-based platform revealed that the output voltage of the NIBB converter is stable throughout the entire transition region, without any efficiency tradeoffs. The input voltage of the converter that was provided by a Li-ion battery was 2.7-4.2 V, and the output voltage was 1.0-3.6 V, which is suitable for radio-frequency power amplifiers. The switching frequency was 500 kHz, and the maximum load current was 450 mA.