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Original question:

BQ51050B BQ2970: BQ29700DSET over discharge protection below 2.8V - Battery recharging not happening

BQ2970: Over discharge protection and release problem

Hafiz Haja
Intellectual 500 points
Part Number: BQ2970
Other Parts Discussed in Thread: BQ51050B

Hi,

As described in the related thread created previously, we are using battery protection IC bq29700 to protect 210mAh Li-Ion battery PGEB014461. When the battery voltage is drained below 2.8V, battery over discharge status is detected and battery is getting disconnected from further loading. When the charger is connected the over discharge status is never getting released and therefore battery is not at all charging. Actually battery is charging in the over discharge detection delay time 144ms only. In the previous thread we didn't got any solution for this issue. Once the battery is very slowly charged above 2.85V or 2.9V with the help of 144ms interval, we need to short the battery negative terminal and module to ground to initiate proper charging. As an end product this won't be good for us. Kindly help for finding a solution for this. Why bq29700 is not properly detecting that a charger is connected to charge the battery so that it should release over discharge state.

Note: Battery charger charge current is between 160mA to 210mA.

Regards

Hafiz

  • 0
    Intellectual 500 points
    Hi,

    Adding to the above notes:
    In the datasheet it is given that "If a charger is connected to a battery in over-discharge state and the voltage detected at the V– is higher than
    –0.7 V, the device releases the over-discharge state and allows the DOUT pin to go high and turn ON the
    discharge FET once the battery voltage exceeds over-discharge detection release hysteresis voltage (VUVP +Hys)". Once the charger is connected the voltage between V- pin and Vss (BAT-) pin is around 1.89V which is greater than -0.7V. So the device releases the over-discharge state only when the battery is charged above Vuvp+hys = 2.8V+0.1V = 2.9V. Since the battery is disconnected already from the circuit and will be connected to circuit for 144ms alone in order to check the over discharge status, how the battery will get charged fast to come out of hysteresis?. We tried charging the battery for more than 6 hours in this condition and battery charge has increased by 20 - 30mV alone.

    Is there anything wrong in my understandings. Kindly support.

    Regards
    Hafiz
  • 0 in reply to Hafiz Haja
    TI__Guru* 76230 points
    hi Hafiz

    Are you certain the issue is with the bq2970. Some scope shots of the charger voltage, the gate of the fet and the battery voltage would be useful to understand what is going on. Do you also have the schematic? You would also want to look into your charger to make sure it is functioning properly. Try using a power supply instead of the charger to ensure that it is not the charger that is the culprit.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 500 points
    Hi Onyx

    Thanks for your reply.

    I got one point which we can suspect could be the issue. We are using BQ51050B as the battery charger IC. It has one feature called precharge mode. If the battery voltage is less than the precharge threshold of 3.0V +-1.0V, BQ51050B will enter into precharge mode. In this mode when the wireless charger is used, BQ51050B will charge the battery with charge current equal to 20% of maximum charge current. The maximum charge current of BQ51050B is set to around 160mA. So 20% of 160mA equal to 32mA only is there to charge the battery. Will this 32mA current drive is not charging the battery fast enough before BQ2970 is setting battery over discharge protection status when the battery voltage is around 2.8V to 2.9V?.

    Regards
    Hafiz
  • 0 in reply to Hafiz Haja
    TI__Guru* 76230 points
    Hafiz

    That could be possible. I would encourage you to trouble shoot to see if that is the case. check to see if the conditions for charge are being met. My suggestions for debug mentioned in my earlier post should be a good starting point.

    thanks
    Onyx