JAJSFS8 July 2018 BQ25601D
The device deploys Narrow VDC architecture (NVDC) with BATFET separating system from battery. The minimum system voltage is set by SYS_Min bits. Even with a fully depleted battery, the system is regulated above the minimum system voltage.
When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode), and the system is typically 180 mV above the minimum system voltage setting. As the battery voltage rises above the minimum system voltage, BATFET is fully on and the voltage difference between the system and battery is the VDS of BATFET.
When the battery charging is disabled and above minimum system voltage setting or charging is terminated, the system is always regulated at typically 50mV above battery voltage. The status register VSYS_STAT bit goes high when the system is in minimum system voltage regulation.