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BQ25708: Battery charging in Precharging mode

Volker Placke
Prodigy 140 points
Part Number: BQ25708

Dear support,

in the datasheet is metioned, that a deeply discharged battery is charged in precharge-mode.

What is the function of "VVBAT_UVLO"? Does the charger tries to charge a battery, if the VBAT is below VVBAT_UVLO?

(see 8.3.1 in datasheet)

In the datasheet (see 8.4.1.2) is a sentence "When battery is full or battery is not in good condition to charge, host terminates charge by setting
REG0x12[0] to 1, or setting ChargeCurrent() to zero"

What is the meaning of "in no good condition to charge"? Is this related to the Vvbat_uvlo?

Does the charger tries to charge the battery, even when it is "in no good condition to charge"?

We have tried to charge a battery with 2.0V (Charger programmed to 3S) and the charger does not enter precharge mode.

Regards,

Volker Placke

  • 0
    TI__Mastermind 25800 points
    Hey Volker,

    VVBAT_UVLO is the voltage it would take to bias up the device and communicate when operating solely off the battery. This is not related to the charging of the battery where you have an input at VBUS that is above the VBUS UVLO threshold.

    This is completely up to the end user to determine if or when the battery is not good to continue battery. This could be due to a charger that has been charging for a long time and is not accepting charge, a damaged battery that is too dangerous to charger, etc. But this completely up to the end user to determine.

    The charger is completely host controlled, so it has no ability to make decisions/actions based on battery conditions except for things related to charging parameters like the transitions between LDO mode and PWM mode, CC mode to CV mode, etc.

    As far entering Pre-Charge mode, again this will be entirely user programmed. The only thing our charger will do there is limit the charge current to a particular value in a region we call "LDO mode" where the SYS voltage is regulated well above the battery voltage, such that we are operating the PMOS BATFET as an linear pass element.


    Regards,
    Joel H