A Dual-Input Bidirectional Three-Level Battery Charger Using Coarse-Fine <i>V</i> _CF Balancing and Frequency Foldback Control for Foldable Mobile Applications

Foldable mobile applications recently have been leading the battery charger to have a slim height with a small form-factor and high efficiency at higher input voltages to increase the power density. Another trend for mobile applications is the power sharing, which enables to supply two mobile devices simultaneously. To meet these requirements, this article presents a dual-input bidirectional three-level battery charger. With the dual-input bidirectional structure, it can support the battery charging while supplying the wireless power-sharing device at the same time. Besides, a proposed coarse-fine flying capacitor voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$</tex-math> </inline-formula> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CF</sub>) balancer can achieve accurate and fast balancing even during the bidirectional operation. In addition, a frequency foldback controller extends an effective duty ratio to have a wide voltage conversion ratio (VCR). The proposed charger has been fabricated using a 130-nm BCD process with a total chip area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.4\times 4.2$</tex-math> </inline-formula> mm. It achieves a seamless bidirectional operation with a well-balanced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$</tex-math> </inline-formula> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CF</sub>, a peak charging efficiency of 96.8%, and a maximum VCR of 92.9%.