A Hybrid Bidirectional Converter With Always-Half-Inductor Current Using Adaptive Target Current Tracking for USB-to-2-Cell Applications

Abstract

This article presents an always-half-inductor- current hybrid bidirectional converter (AHI-HBC) for USB- to-2-cell bidirectional power transfer. The converter achieves always-half-inductor current (AHI) in both directions compared to conventional bidirectional converters (CBCs) while using only 5-V transistors. This enables the elimination of high-voltage (HV) transistors, which have poor ON-resistance ( RON) performance and increase process costs. In addition, to address the challenge of varying charging current caused by changes in a battery voltage (VBAT), we propose a normalized inductor current ( NIL)- based adaptive target current controller that leverages the relationship between the inductor current (IL) and output current to e ffectively regulate the battery charging current ( IBAT). By utilizing the proposed controller, IBAT adaptively tracks the target charging current regardless of VBAT, which varies depending on the state-of-charge. The prototype chip was fabricated in a 180- nm CMOS process with a 4.7- µH inductor, two 10- µF flying capacitors, and a 10- µF output capacitor. With the greatest IL reduction within the target USB-to-2-cell range, the converter demonstrated peak e fficiencies of 97.4% (96%) in the forward mode and 97% (96.2%) in the on-the-go (OTG) mode with an inductor dc resistance ( RDC) of 11.5 m Ω (295 m Ω).