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BQ24171: Pre charging consultation

dxd1412
Prodigy 90 points
Part Number: BQ24171

Hi Jeff:

        Hello, I have some questions about pre charging that I would like to consult with you

Q1：My battery voltage is 4.4V/2A, and the pre charging voltage set is below 3V to start pre charging. But when my battery voltage just drops below 3V, the charging current will jump, not the set 200mA, until it stabilizes at around 2.7V. Is this normal?

Q2：May I ask if there is any way to solve this problem (current jumping during the conversion process from fast charging to pre charging)? I want to switch to 200mA pre charging immediately after the battery voltage drops below 3V. If you have any good suggestions, could you please guide me

  • 0
    TI__Guru*** 148545 points

    Hi dxd,

    Most likely, the issue is not enough hysteresis for BAT_LOWV:

    This issue is made worse if the connection from the charger to the battery is highly resistive or the battery itself has high impedance (e.g. has aged).  Other than reducing the resistance of the connection to the battery, there is no much that can be done.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 90 points

    Hi Jeff

    Why did I confirm the pre charging status on "BQ24171EVM-706-15V", and it wasn't until around 2.7V that I could switch to the pre charging current? Is this a problem with BQ24171?

    I would also like to confirm with you the flashing status of the battery during overvoltage. According to the specifications, the light should flash under overvoltage. Why does my sample not flash? What is the reason for this? Or is it possible to rectify areas that can be debugged again

  • 0 in reply to dxd1412
    TI__Guru*** 148545 points

    Hi dxd,

    The pre to fast threshold is the feedback divider multiplier times the 1.45V voltage above plus/minus the 100mV hysteresis.  The 2.7V is correct.

    What is overvoltage, the battery or the input power?  

    battery voltage:  percentage multiplied by the battery regulation voltage

    input voltage: divided down value on the OVPSET pin

    Regards,

    Jeff