An Inductor-First Hybrid Buck-Boost Converter Featuring Seamless Single-Mode Operation, 97.2% Peak Efficiency, and 565 mA/mm3 Current Density with Ultra-Compact 1 mm3-Volume Inductor

To manage power on mobile devices using batteries, a buck-boost converter has been widely exploited with growing market demand for its step-up and step-down functions. Although a supply voltage $(V_{\text{IN}}=2.9-4.2\mathrm{V})$ from the battery varies, the converter can provide a target output voltage $(V_{OUT}=3.4V)$ by adjusting its voltage conversion ratio $\left(M=V_{\text{OUT}} / V_{\text{IN}}\right)$ between 0.8 and 1.2. This converter highly requires the breakthrough for achieving both high efficiency and high power density. However, these goals are at odds with inductor's large DC resistance (DCR) for employing a compact inductor ($L$). The conventional buck-boost topology suffers from significant conduction loss due to high inductor current $(l_{\mathrm{L}})$, which further degrades the efficiency when a smaller $L$ with higher DCR is used for compact-sized systems. Moreover, large $I_{L}$ ripple $(\Delta l_{\mathrm{L}})$ due to wide voltage swing across $L$ necessitates a bulky inductor with high inductance.