A Battery-to-3.4 V Hybrid Buck-Boost Converter With Always Reduced Conduction Loss

Abstract

This article presents a hybrid buck-boost converter designed for lithium-ion battery-powered mobile devices. The proposed converter consists of four low-voltage power switches and one flying capacitor ( $C_{\text {F}}$ ). Unlike the conventional buck-boost converters (CBBCs) that employ two power switches in series with an inductor, this converter uses only one. The $C_{\text {F}}$ , which is paralleled with the inductor (L), facilitates charge transfer to the output capacitor in the buck mode and distributes input current in the boost mode. This configuration significantly reduces inductor current across the entire input voltage ( $V_{\text {IN}}$ ) range. By leveraging the low-voltage stress of power switches and reduced current stress of inductor, the conduction loss (CDL) of the power switches is reduced by up to 64% compared with other studies with equivalent silicon areas. The converter was fabricated with a $0.18~{\mu }$ m bipolar-CMOS-DMOS (BCD) process using only 5-V devices. Measurement results show that the converter achieves a peak efficiency of 98.6% with a small dc resistance (DCR) of 8 m $\Omega $ and maintains a peak efficiency of 97.3% with a larger DCR of 170 m $\Omega $ . Moreover, the converter achieves an on-die current density of 1.47 A/mm².