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Why is BQ27210 running so hot?

HarriSiirtola
Intellectual 925 points
Other Parts Discussed in Thread: BQ27210

I made my own board, following exactly the schema and layout of the BQ27210 EVM. The gauge shows temperatures over 40C (NTCBIAS is set as internal). The screenshot in the EVM manual shows a value which converts to 35.5C which lead me thinking it could be normal. However, running the EVM shows temperatures around 27-28C.

I even checked this with a thermographic camera and the gauge certainly is the warmest spot on the board. The circuit shouldn't draw more than 90uA, so it shouldn't dissipate any heat. Can anyone suggest what could be wrong?

Best Regards,

       Harri

  • 0
    Intellectual 925 points

    I suppose nobody else has run into  this. One further observation: the temperature seems to be slightly proportional to the charging current, which I don't completely understand. I mean, why would current flowing through the shunt resistor cause heating inside the gauge IC? Furthermore, discharging current doesn't seem to heat the chip. Strange.

  • 0 in reply to HarriSiirtola
    TI__Genius 14985 points

    How close is the bq27210 to your battery?  The idea is to monitor the temperature of your battery and batteries do self-heat significantly during charge and discharge.

  • 0 in reply to dMax
    Intellectual 925 points

    It's not close, it's connected with a 10cm wire. That would indeed explain the heating but it's not the case. Heating seems to be proportional to the charging current, though. With 50mA, there's no excess heating but over that it gradually rises (with ~80mA charging it's ~40C). I can't see why, because the current only flows through the shunt resistor (which isn't heating). I've started ignoring that because the temperature is within specs and the chip remains functional so far. I'm still interested why this happens.

  • 0 in reply to HarriSiirtola
    TI__Genius 14985 points

    Wrong temperature readings will affect your gauging accuracy, so it would be good to figure it out.

    The only reason the IC would be that hot itself would be if it were damaged somehow and/or if some pins were biased incorrectly and had inappropriate current through them.  Can you try to replace it?  Does it happen on all of your boards?

  • 0 in reply to dMax
    Intellectual 925 points

    Hi, sorry for the delay in replying.

    I've tried to follow the EVM schematic quite exactly. Currently I have just one working device ( I slipped a probe and damaged the other board) but the heating did happen on the other one before. I don't have extra chips for replacement. I'm going to use an external NTC for observing the battery temp in the future, so this won't be a problem unless it damages the gauge chip.

    I'll still try to figure out something, please reply if you have any suggestions. Thanks!