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BQ21040 does not charge the battery module with PCM when battery is fully discharged.

Youngsoon Choi
Prodigy 20 points
Other Parts Discussed in Thread: BQ21040, BQ24040

Hello.

When the battery is not fully discharged, BQ21040 operates well.

But, When the battery is fully discharged and the battery protection module of battery detects over discharging, I can not charge the battery.

The OUT pin of BQ21040 is around 0.4V only. There is no battery detection waveform on OUT pin.

I used 1K ohm between Iset and GND. and 10K ohm between TS and GND. Battery is always attached.

Thank you.

  • 0
    TI__Genius 11480 points

    Hi Youngsoon,

    What battery protector are you using?

    Is this problem occuring with the adapter inserted, or battery only?

    If in battery only, the protection FETs will turn off when overdischarged, and you will need to trickle charge the battery to wake up the protector. 

  • 0 in reply to David Wiest Jr
    Prodigy 20 points

    First, thanks for the quick answer.

    1. The battery module is fully discharged or the output terminal is shortened to make the over-discharge protection circuit active.

    2. The charging circuit using the BQ24040 releases the protection of the battery module and starts charging, but the charging circuit using the BQ21040 fails to start charging. So I think the battery module is not abnormal.

    3. How do I add trickle charging to the charging circuit using the BQ21040?

  • 0 in reply to Youngsoon Choi
    TI__Genius 11480 points
    What precharge current are you using for both the 24040 and the 21040? Are they the same?


    My thought process is that the protector may need some small current to allow for precharge. If the 21040 is larger (fixed at 20%), the protector may not allow it.