Low-frequency ripple-shaping controller for operation of non-inverting buck-boost converters near step-up step-down boundary

This paper introduces a practical controller for low power noninverting dc-dc buck-boost converters that minimizes the step-up step-down mode transition problem, while also significantly improving power processing efficiency compared to existing state-of-the-art solutions. Near the step-down step-up boundary, the controller enters a low-frequency ripple shaping mode of operation that allows lower operation frequency than in conventional buck or boost modes without paying a penalty of increased ripple, i.e. RMS, current. As a result, both switching and conduction losses are reduced. Furthermore, since the ripple shaping mode can cover both buck and boost modes of operation, mode toggling problems are practically eliminated. The effectiveness of the controller is demonstrated with a 1.8 V to 5 V input, 3.3 V/10W output experimental prototype where stable operation, smooth mode transitions, and power processing efficiency improvements of up to 6% are demonstrated.