The charger employs a synchronous buck-boost converter that allows charging the 1s to 4s battery from a legacy 5V USB input source, HVDCP and USB-PD power sources. The converter operates uninterruptedly and continuously in buck, boost or buck-boost mode depending on the input to system output voltage difference. When the input voltage is close to the system output voltage, the converter operates in a proprietary buck-boost mode.

With a battery attached at BAT and input power at VBUS, the charger can provide at least the MINSYS voltage at SYS and charge current for the battery at BAT. Once the battery voltage reaches the MINSYS voltage, the SYS voltage follows the BAT voltage up. With no battery attached to BAT and input power at VBUS, the voltages at SYS and BAT vary depending on the whether or not charge is enabled as explained below.

1. No battery or battery removed and charge disabled by CE pin or EN_CHG register or thermistor removed from TS pin - The charger keeps the BAT pin voltage at low-level, steady-state voltage and regulates SYS pin to MINSYS. The host can monitor the ADC BAT pin voltage and TS fault register to determine when a valid battery is attached.
2. No battery or battery removed while charge enabled and TS pin function is disabled - The charger continuously tries to charge the BAT capacitance, typically resulting in the BAT voltage alternating between a low level and BATOVP fault. The SYS voltage follows the battery voltage up, potentially reaching SYSOVP fault. In order to determine if a battery is attached, the host must periodically disable charge, force IBAT discharge current and then read the ADC BAT pin voltage. Alternatively, the host can monitor the INT pin for rapid interrupts and then read the charge status bits for fast (<1 s for typical BAT pin capacitance) toggling between charging, taper and termination.