CHARGER manages battery current flow to maintain VSYS voltage.
The battery is isolated when VBUS is connected and the battery is fully charged. Under this condition, VBUS supplies VSYS. When VBUS is disconnected, VSYS is supplied by its decoupling capacitors until it is connected to VBAT. The connection is triggered by VSYS reaching VSYSBELOW_VBAT level and is completed within tSWITCH.
After VBUS has been connected (and debounced), VSYS is disconnected from VBAT and supplied by its decoupling capacitors until supplied by VBUS, which happens within tSWITCH.
The system load requirements are prioritized over battery charge current when VBUS is connected and the battery is charging. During charging, if the system current load exceeds IBUSLIM, the battery charge current decreases to maintain the VSYS voltage. CHARGER reduces the current to maintain an internal voltage of VCHDROPOUT above the VBAT voltage. If more current is required, CHARGER enters the SUPPLEMENT state to provide current from the battery, up to IBATLIM.