SLUSDF9 June 2020 BQ25790
The device terminates a charge cycle when the battery voltage is above the recharge threshold, the converter is operated in the battery constant voltage regulation loop and the current is below the termination current. After the charging cycle is completed, the BATFET turns off. The converter keeps running to power the system and the BATFET can turn on again if the supplement mode is triggered.
When termination is done, the status register CHG_STAT is set to 111 and an INT pulse is asserted to the host. Termination is temporarily disabled when the charger device is in input current (IINDPM), input voltage (VINDPM) or thermal (TREG) regulation. Termination can be permanently disabled by writing 0 to EN_TERM bit prior to charging termination. Writing 0 to EN_TERM when the termination already occurred or in the top-off charging stage does not disable termination, until the next charging cycle has been restarted. If termination is reenabled by setting EN_TERM = 1 during the current charge cycle, the change is applied immediately to the current charging cycle.
At low termination currents (like 40mA to 160mA), due to the comparator offset, the actual termination current may be up to 20%~40% higher than the termination target. In order to compensate for the comparator offset, a programmable top-off timer (default disabled) can be activated after termination is detected. Whlie the top-off timer is running, the device continues to charge the battery in constant voltage mode (BATFET stays on) until the top-off time expires. The top-off timer follows safety timer constraints, such that if the safety timer is suspended, so is the top-off timer. And if the safety timer is doubled, so is the top-off timer. CHG_STAT reports whether the top off timer is active via the 110 code. Once the top-off timer expires, the CHG_STAT register is set to 111 and an INT pulse is asserted to the host.
The top-off timer gets reset (set to 0 and counting resumes when appropriate) for any of the following conditions:
Once the charger detects termination, the charger reads the top-off timer (TOPOFF_TMR) settings. Programming the top-off timer value after termination has no effect unless a recharge cycle is initiated. The top-off timer only starts to count when the charger's termination criteria are met. If EN_TERM = 0, the charger never terminates charging, so the top-off timer does not start counting, even if it is enabled. An INT is asserted to the host when the top-off timer starts counting as well as when the top-off timer expires. All charge cycle related INT pulses (including top-off timer INT pulse) can be masked by CHG_MASK bit.