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

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 <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small>-resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\mathrm { ON}}$</tex-math> </inline-formula>) performance and increase process costs. In addition, to address the challenge of varying charging current caused by changes in a battery voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm { BAT}}$</tex-math> </inline-formula>), we propose a normalized inductor current (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{\mathrm { IL}}$</tex-math> </inline-formula>)-based adaptive target current controller that leverages the relationship between the inductor current (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{L}$</tex-math> </inline-formula>) and output current to effectively regulate the battery charging current (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\mathrm { BAT}}$</tex-math> </inline-formula>). By utilizing the proposed controller, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\mathrm { BAT}}$</tex-math> </inline-formula> adaptively tracks the target charging current regardless of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm { BAT}}$</tex-math> </inline-formula>, which varies depending on the state-of-charge. The prototype chip was fabricated in a 180-nm CMOS process with a 4.7-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>H inductor, two 10-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>F flying capacitors, and a 10-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>F output capacitor. With the greatest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{L}$</tex-math> </inline-formula> reduction within the target USB-to-2-cell range, the converter demonstrated peak efficiencies of 97.4% (96%) in the forward mode and 97% (96.2%) in the on-the-go (OTG) mode with an inductor dc resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\mathrm { DC}}$</tex-math> </inline-formula>) of 11.5 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula> (295 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula>).