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BQ24725A: Charger issue for the pack

Zhang Liang
Genius 4205 points
Part Number: BQ24725A

Hi,

We use thte BQ24725A for the battery charger, and there are 3 cell lithium battery series,

Now the output voltage of the Vbatt_chg isn't 12.6V if there are no battery connect or the battery capacity is zern,

The schematic diagram as the attach, please kindly advise why the output voltage is abnormal for the Vbatt_chg 

  • 0
    TI__Genius 11385 points

    Hi Zhang,

    The charge voltage is set in 0x15H. 

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    Genius 4205 points

    Hi Pengzhao,

    Thanks for you kindy comment;

    We have set the 0x15H and the output voltage is 12.6V when the bettery capacity don't' empty;

    But the output voltage isn't 12.6V when we remove the battery or the battery bettery capacity is empty;

  • 0 in reply to Zhang Liang
    TI__Genius 11385 points

    Hi Zhang,

    What do you mean battery capacity is not empty or empty? Can you define a voltage level when it is empty or not empty?

    Usually the battery terminal voltage is dominated by the voltage of the battery itself. If you don't enable charge and there is no energy storage device at the battery terminal, then the voltage level is not defined.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    Genius 4205 points

    Hi Pengzhao,

    Sorry my confuse discription;

    We have the below issue for this chip:

    1. We can charger the battery if the battery voltage is higher than 8V when power on, and the chager voltage(Vbatt_chg) is 12.6V;

    2. We can not chager the battery if the battery voltage is lower than 8V when power on, and the chager voltage is 0V;

    3. We remove the battery, and enable the EC, the charger voltage is 0V;

    So we have no idea the above issue and please help to analyse, we can provide the detail file if your need, thanks.

  • 0 in reply to Zhang Liang
    TI__Genius 11385 points

    Hi Zhang,

    There is something I noticed about the statements you made.

    VBATT_CHG will never be 0V even if the battery voltage is lower than 8V. VBATT_CHG is only determined by battery voltage. If there is a battery there, it will never be 0V.

    The fact that you see 0V at VBATT_CHG indicates to me that it is an issue potentially with your gauge/protector/monitor. You may have triggered some protection on your battery pack and the pack opened. Recommend checking that aspect.

    I would also recommend getting an EVM and ensure both the EVM and your design operate the same under a certain test condition.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    Genius 4205 points

    HI Pengzhao,

    Thank for your kindly suggesting.

    And we have the other situation: we don't connect the battery, and enable the EC, but the VBATT_CHG is still 0V output, so please advise if there are any error, thanks.

  • 0 in reply to Zhang Liang
    TI__Genius 11385 points

    Hi Zhang,

    If you enable charge and there is no battery there, the charger will treat the caps as battery and charge it to regulation voltage (set by 0x15).



    The normal behavior should be the following:

    1. Battery exists. Enable charge -> voltage dominated by battery
    2. Battery does not exist. Enable charge -> voltage goes up to regulation voltage set by 0x15 because the charger charged the caps. 

    If your case 1 is working, then your case 2 should work as well. If your case 1 is not working, then the direction to debug is different.

    Recommend testing an EVM.

    Thanks,

    Peng