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Original question:

BQ29700: How to prevent tripping during connection

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

Hafiz Haja
Intellectual 490 points
Part Number: BQ2970
Other Parts Discussed in Thread: BQ51050B

Hi,

In our design we are using BQ51050BRHLT as battery charger and BQ29700DSET as battery protector. BQ29700DSET will make battery terminals open when battery discharges below the under voltage threshold level of 2.8V. Below this threshold the protector IC is opening the short between module GND and battery negative. Once the battery voltage is going below 2.8V we are unable to recharge the battery using wireless charger. We need to remove battery and charge it above 2.8V, then only recharging is happening. We came across the note that once the battery is mounted, we need to short V- pin to battery GND or connect a charger will solve the issue. Connecting the charger is helping the short between module GND and battery negative to happen, but this happens only when battery voltage is greater than 2.8V. If the battery is drained below 2.8V, we are facing issue. Kindly suggest a solution for the issue.

Regards

Hafiz

  • 0
    Intellectual 490 points

    Hii,

    Any one can come up with a solution or any idea what may be the problem?

  • 0 in reply to Hafiz Haja
    TI__Guru 54715 points
    Hi Hafiz,
    When in the Over-Discharge Status mode the bq2970 is expecting the charger to restore the voltage on the pack terminals before it turns on the FET again. It applies a load of RV–D.
    It would seem with the battery protected in Over-Discharge Status the charger is likely to see the battery terminals as a voltage below VBAT(SC) and charge very slowly. Once the voltage is above the VBAT(SC) level it should provide the precharge current. If the bq51050B can not provide enough current to overcome the system load on the pack pins as well as the pull up resistor value of the bq2970, the system will not start up. Check your settings for the bq51050B currents.
  • 0 in reply to WM5295
    Intellectual 490 points

    Hi,

    We are using Li-Ion battery of capacity 180mAh and we are limiting the battery charger bq51050B charge current to 160-170mA. There is no current requirement specified in the battery protector bq2970 datasheet. What is the minimum charge current from battery charger bq51050B required for protector bq2970 to release Over-Discharge Status?

    Thanks for the support.

    Regards

    Hafiz

  • 0 in reply to Hafiz Haja
    TI__Guru 54715 points
    Hi Hafiz,
    The bq2970 data sheet describes the pull up of V- during UV as a resistance RV-D in section 8.5. 100k to 550k is shown as the range. The current will depend on the applied voltage. If the charger goes to 4.2V, current needed could be as much as 4.2/100k or 42 uA, but perhaps less since the battery voltage would be low and the V- should be driven to a recovery voltage before the charger reached full voltage.