8.2 A 96.9%-Peak-Efficiency Bilaterally-Symmetrical Hybrid Buck-Boost Converter Featuring Seamless Single-Mode Operation, Always-Reduced Inductor Current, and the Use of All CMOS Switches

The buck-boost converter is essential for managing power on mobile devices that use batteries. It works by regulating the output voltage (V₀=3.4 ~V) with a specific voltage conversion ratio (M=V₀ / VIN), given a supplied voltage (VIN=2.7 ~ 4.2 ~V) that fluctuates based on the battery's state-of-charge. In traditional non-inverting buck-boost topology, the inductor current (IL) is typically greater than the output current (I₀), leading to a significant conduction loss attributed to the inductor's series resistance (DCR) and the switches' on-resistance (.RON). Thus, many hybrid attempts involving flying capacitors (CF) have been made to reduce IL. The approaches in [1–3] are able to decrease IL to be equal to I₀, but only in the boost mode (M > 1), due to their design that directly connects the inductor to the output. When compared to a conventional buck converter, these methods are ineffective at reducing IL in the buck mode (M < 1). Moreover, a discontinuous mode change between M > 1 and M < 1 is mandated when VN ≈ V₀, adding to the design complexity with the necessity for intricate voltage-sensing and mode control. To address this, single-mode buck-boost converters [4, 5] were introduced. However, [4] forfeits the benefit of IL-reduction in the boost mode (IL=M · I₀), and both [4, 5] necessitate the use of high-voltage-rating switches (e.g., LDMOS) that exhibit a poor RON. Although the design of [6] may appear ideal in aspects of both IL-reduction and switches' voltage stress, the substantially differing bias voltage of CF in buck and boost modes renders the mode change extremely difficult at M ≈ 1.