A 29.5W Switched-Capacitor based Dual-Output Hybrid Secondary Charger Providing Simultaneous Two-Cell Battery Charging and System Supply Voltage with Input Current Limiting Feature

The fast charging system for a two-cell battery typically consists of primary-secondary charging configurations followed by a buck converter to provide the system supply voltage (Vsys) [Fig. 1 (top)]. Recent works on efficient battery charging have focused on the primary charger capable of operating both as a voltage and current source [1] –[5]. By contrast, the secondary charger only needs to function as a current source, providing substantial charging current during the constant current (CC) mode. Among various secondary charger architectures, the 2:1 switched-capacitor (SC) power converter is highly favored due to its remarkable efficiency [6]. The SC converter can maintain a relatively constant charging current by adjusting the input voltage $\left(\mathrm{V}_{\mathrm{IN}}\right)$, relying on software communication between the USB input and the charger.