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BQ20Z95 Ra Table problem

Patrick Loef
Prodigy 60 points

Hello,

We are using the bq20z95 gas gauge together with the LTC4100 charger. This works fine, but we seen after a little while that the gas gauge acts very strange. 

On a certain moment the gas gauge reports that the li-ion battery's(4S3P) are full, but when you look at the cell voltage, there no bigger then 3500mV.

The full charge capacity gives a value of about 65535mAh and after an reset it gives the value of 0mAh and the gas gauge still reports he 100% full.

When I look in the Ra Table I see for R_a0, R_a1, R_a2, Ra_3 that the values of Cellx R_a0...Cellx R_a14 are -32767 num. 

After is send my original .gg file the problem is solved, but after a little time the problem is back again.

What can be wrong here? I have made an .gg file where you can see the strange values of the Ra Table, this file i have added to the post

Kind regards

Patrick

test.zip
  • 0
    TI__Genius 10235 points

    This looks like it could be flash corruption. After you reload the default GG file, what exactly happens before this corruption occurs? What kind of environment is the pack in?

    Another potential cause could be related to your sense resistor. Is it really 75 mOhm? That is pretty high. The typical sense resistor value is 10mOhm. The issue with such a high sense resistor is that it severely limits the maximum current allowed. The coulomb counter can only handle about 200mV between SRP and SRN. This is less than 3A with a 75 mOhm sense. If that isn't the value you expect, then you need to take a look at it. If there is a problem with the sense resistor, then the gauge could be reading junk data and that can also cause odd Ra values. Also, make sure the cell voltages are being reported accurately by the gauge.

  • 0 in reply to Chase7071949597
    Prodigy 60 points

    The pack is build in a device and cannot be removed from it. It can only be removed when the device is put open. It is Li-Ion pack, the cells are from Panasonic.

    Everything looks normal, if you charge the battery pack it goes until is 100%, the cell voltages are then 1 a 2mv different from each other. Then we let the device on so the pack can discharge. We see that the pack discharge, the relative state of charge goes lower. 

    When the pack is empty the device shutdown, then we put in the charger and the device will start-up again. When we look then to the pack information, we see that the relative state of charge is 100%, instead of 0%.

    The pack voltage is about 12V a 13V and the cell voltage about 3.3V, the relative state of charge is the same as remaning capacity and full charge capacity, the value of remaning capacity and full charge capacitiy is then about 6000mA. The absolute state of charge is 0%, BatteryStats = 0x0080, BatteryMode = 0x0001, CycleCount = 0, MaxError = 0%, StateofHealth = 100.

    Also we see that the battery is charging, this will stop after a while, because the BQ thinks he is overcharged. When the charger is disconnected, then the Remaining capacity and full charge capacity change to a value more then 65000mA, the BatteryMode is then 0x0001 and the BatterStatus is 0x02C0, the pack voltage is about 14.4V and the cell voltages about 3.6V.

    When we reset the pack, this will not help. The only thing what will help is to load .gg file again, and the cycle start again as described above. I also programmed the BQ with the .senc file and the .gg file so everything would be correct.

    We see this problem with more of our package, we had at this point already 6 pack who has this problem.

  • 0 in reply to Patrick Loef
    Prodigy 60 points

    And also the placed sense resistor is 75mOhm