Digital Noninverting-Buck-Boost Converter with Enhanced Duty-Cycle-Overlap Control

The nonideal effects of the comparator and dead time in a synchronous controlled dc-dc converter adversely affect the stability of a four-switch noninverting-buck-boost (NIBB) converter. The pulse-skipping phenomenon occurs in the mode-transition region near the boundary between the step-down and step-up regions, and this phenomenon leads to an unstable output voltage and an unpredictable output voltage ripple. However, these two results may damage the entire power system and application system. This brief proposes an enhanced duty-cycle-overlap control technique for a digitally controlled NIBB converter. The proposed technique offers two duty cycle limitations for various conditions in the mode-transition region and ensures the stability of the digital controller and output voltage. Moreover, this technique involves combining the duty cycles of both step-down and step-up modes for deriving an accurate value of the output voltage. The experimental results derived from a digital controller implemented through a field-programmable-gate-array-based platform revealed that the output voltage of the NIBB converter was stable throughout the transition region. The observed input voltage of the converter, provided by a Li-ion battery, was 2.5-4.5 V, and the output voltage was typically 3.3 V, which is suitable for communication systems, audio systems, and I/O pad power supplies. The switching frequency was 1 MHz, and the maximum load current was 500 mA.