Charging IC-NVDC Architecture (with BQS24259 as an example)

The BQS24259 uses a nvdc (narrow-voltage DC) architecture that uses BATFET to separate the system from the battery, and the minimum systems voltage is set by reg01[3:1], even if the battery is completely depleted, and the system is set to the minimum system voltage (default 3.5V).

When the battery voltage is below the minimum system voltage set, then the BATFET will run in linear mode (LDO mode), and the system will be 150mv higher than the set system voltage, and when the battery voltage rises to a higher than the minimum system voltage, the BATFET will open completely, and the voltage difference between the system and the battery is Batfet RDS, and when the system voltage is the lowest voltage adjusted, the status register Reg08[0] will become higher.

The system voltage is always adjusted above the battery voltage of 70mv when the battery is charged to the end or the battery is above the minimum system setting voltage, as shown in the figure below.