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BQ25895: BQ25895 battery voltage error

Julhio
Intellectual 310 points
Part Number: BQ25895

Normaly, when the BQ25895 is powered on without the battery the VBAT is 2,304V, but sometimes it shows 4,084V.

In normal condition, the registers is:

And the REG0B change of 0x76 to 0x7E every time.

How do I know if the battery is present to notify battery error ?

Thanks

  • 0
    TI__Expert 8230 points
    Hello Julhio,

    This is expected behavior in cases where charging is enabled and there is no battery present. If no battery is present, the decoupling cap at the BAT pin will be charged to VREG (4.2V in this case) and the charger will report Charge Terminated. The decoupling cap will discharge and once the voltage reaches VREG- VRECHG (4.2V- ~100mV) it will begin charging again and report "Fast Charging".

    When operating without battery, we recommend customers to disable charging to avoid this behavior.

    The bq25895 has a feature called BAT_LOADEN which provides an internal battery load minimum of 15mA to facilitate battery detection. The host can use this load together with the internal ADC to determine battery presence.
  • 0 in reply to Fernando Lopez
    Intellectual 310 points

    You said to use the BAT_LOADEN to facilitate battery detection, but I didnt understand how can I do it.

    The internal ADC only provides Input Voltage, Temperature and Charge Current.

    What is the logic to detect the battery ?

    Thanks

  • 0 in reply to Julhio
    TI__Expert 8230 points

    Hello Julhio,

    The internal ADC provides VBAT, VSYS, VBUS, ICHG and TS data. Register 0X0E holds the ADC conversion of battery voltage.

    A function can be implemented that does the following:

    • Enable battery charging
    • Set Disable charge when charge is done.
    • Enable BAT_LOADEN for 10ms to discharge BAT
    • Start the ADC to measure the VBAT.
    • If VBAT>4V, then the battery is attached, otherwise the battery is not present since the BATLOAD_EN load would have discharged the decoupling cap on the BAT pin.
    • Disable BAT_LOADEN.

    Once battery presence has been determined, the host can disable charging if the battery is not present.