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 charger operates in buck, buck-boost or boost mode based on different input voltage and output voltage combinations. The converter can operate uninterruptedly and continuously across the Buck, Buck-boost and Boost operating states.

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.

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 funtion 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 but the converter never allows SYS to fall below the MINSYS threshold even if the BAT voltage falls below MINSYS. In order to determine if a battery is attached, the host must perididcally 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) toggling between charging, taper and termination.