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

Abstract

The buck-boost converter is essential for managing power on mobile devices that use batteries. It works by regulating the output voltage $\left(V_{0}=3.4 \mathrm{~V}\right)$ with a specific voltage conversion ratio $\left(M=V_{0} / V_{\text {IN }}\right)$, given a supplied voltage $\left(V_{\text {IN }}=2.7 \sim 4.2 \mathrm{~V}\right)$ that fluctuates based on the battery’s state-of-charge. In traditional non-inverting buck-boost topology, the inductor current $\left(I_{\mathrm{L}}\right)$ is typically greater than the output current $\left(I_{0}\right)$, leading to a significant conduction loss attributed to the inductor’s series resistance (DCR) and the switches’ on-resistance ($\left.R_{\mathrm{ON}}\right)$. Thus, many hybrid attempts involving flying capacitors $\left(C_{\mathrm{F}}\right)$ have been made to reduce $I_{\mathrm{L}}$. The approaches in [1–3] are able to decrease $I_{\mathrm{L}}$ to be equal to $I_{0}$, but only in the boost mode $(M \gt 1)$, 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 $I_{L}$ in the buck mode $(M \lt 1)$. Moreover, a discontinuous mode change between $M \gt 1$ and $M \lt 1$ is mandated when $V_{\mathbb{N}} \approx V_{0}$, 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 $I_{\mathrm{L}}$-reduction in the boost mode $\left(I_{L}=M \cdot I_{0}\right)$, and both [4, 5] necessitate the use of high-voltage-rating switches (e.g., LDMOS) that exhibit a poor $R_{\mathrm{ON}}$. Although the design of [6] may appear ideal in aspects of both $I_{L}$-reduction and switches’ voltage stress, the substantially differing bias voltage of $C_{\mathrm{F}}$ in buck and boost modes renders the mode change extremely difficult at $M \approx 1$.

Topics & Concepts