A Dual-Input Bidirectional 3-Level Battery Charger with Coarse-Fine VCF Balancing and Wide VCR for Foldable Mobile Applications

The on-going trends for foldable mobile phones require smaller form factors and high-density battery charging with a wide-input range to reduce the battery charging time. Thus, multi-level or hybrid converters can be a solution to reduce the size of passive devices and to achieve a higher efficiency at high input voltages compared with 2-L converters [1]–[4]. Another trend for mobile applications is wireless power sharing, which allows one mobile device to charge another device (e.g., smart watch, phone, or earbuds). If a travel adapter (T.A) is attached to the mobile device, wireless power sharing can allow two devices to be charged at the same time. To support this feature, the dual-input bi-directional 3-level charger is proposed as shown in Fig. 21.2.1 (top left). The dual-input SWs ($D_{\text{CHG}}$ and $D_{\text{wc}}$) support wired and wireless battery charging, respectively, while the USB on-the-go $(0.\mathrm{T}.\mathrm{G})$ and wireless power sharing are connected to each switch. Figure 21.2.1 (top right) presents the proposed bi-directional charger operations. When the power sharing is activated with a load current $(/_{\text{TX}})$ during battery charging, the adapter increases the charging current $(l_{\text{CHG}})$ to supply power to $V_{\text{wc}}$ while simultaneously charging the battery. As the wireless device requires more current from $\prime_{\text{TX}}, /\text{cHG}$ increases until it reaches an $/\text{cHG}$ regulation level. Then, the $l_{\text{DHC}}$ regulation current dominates while $1_{\text{BAT}}$ decreases. $\vert \mathrm{f}l_{\text{TX}}$ further increases to a heavy load, $I_{\text{DHG}}$ is no longer sufficient to provide both $\prime_{\text{TX}}$ and $1_{\text{BAT}}$ and as a result the battery begins to supply the insufficient current to $V_{\text{wc}}$, At this point, the inductor current $(I_{\text{ND}})$ flows from the battery to the input, where the charger operates as the boost converter because the battery becomes a supplier. When the adapter is detached, the charger supplies power from the battery while regulating the bypass voltage $(V_{\text{BYP}})$. In a prior work [5], a bidirectional 3-L charger was presented. However, it does not support a seamless mode transition between the buck and reverse boost operations.