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BQ25731: What does it do with respect to voltage and current supplied to the battery?

John Winters
Prodigy 80 points
Part Number: BQ25731

There is very little detail.

For example, people ask things like this:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1008691/bq25731-does-bq25731-have-pre-charge-function?tisearch=e2e-sitesearch&keymatch=BQ25731#

and they get an answer which seems not to include constant voltage mode.

How does one handle the trickle, constant current, constant voltage, charge complete situations?  What does the device to to support these? Data sheet is silent.

  • 0
    TI__Genius 11385 points

    Hi John,

    BQ25731 is a host-controlled charger, so we left a lot of flexibility there.

    You can tell which mode the charger is in by the actual charge current and battery voltage (both obtainable by charger ADC).

    For example, it is in constant current (CC) mode when the actual charge current is what you set in the register (03/02h) + battery below charge voltage register setting.

    On the other hand, if you see that actual charge current is below charge current (03/02h) setting + battery voltage close to charge voltage register setting, it is in CV mode.

    Depending on application, the MCU is free to act (such as terminate charging) accordingly anytime during the charge cycle.

    I hope this answers your questions from both E2E threads.

    Thanks,

    Peng

  • 0 in reply to Pengzhao Zhu
    Prodigy 80 points

    There is still the issue of when to do trickle charging.. am I to assume that this is left ot the uP to monitor as well?

    And charge termination upon reaching the lower current limit?  Is this done by the BQ or is it initiated at the whim of the uP?

  • 0 in reply to John Winters
    TI__Genius 11385 points

    Hi John,

    MCU has full control of the charging cycle. MCU need to monitor the full charging cycle if you wish to know what stage of charging it is in. It doesn't have a status register that indicates which charging mode it is in.

    Regarding termination, please see the following from the datasheet:

    "When battery is full or battery is not in good condition to charge, host terminates charge by setting CHRG_INHIBIT bit to 1b, or setting ChargeCurrent() to zero(WDTMR_ADJ=00 should be configured to disable watch dog timer, otherwise charge current will reset to 256 mA after watch dog timer expires)."

    Thanks,

    Peng