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Overheating of BQ27441-EVM-G1B fuel gauge upon initial connection

Chintan Pathak4
Intellectual 845 points
Other Parts Discussed in Thread: BQSTUDIO, EV2400

Dear Forum, 

I recently ordered a bunch of TI battery gauges, and I started work with a BQ-27441-EVM-G1B. It is a system side impedance track fuel gauge. Although it is an old design, I got it, so that I can interface it with a charger I previously had - BQ-24261-EVM. 

When I first connected the device, everything seemed fine. I saw the un-boxing video and found that I didnt have the necessary BIN-pin 10kOhm resistor which I ordered and connected. I had updated firmware on my EV-2400 to the latest v0.18 and connected it to the gauge using an I2C cable. On the PC I am using bqStudio v 1.3.45 and chose the gauge option on startup with number BQ-27441-G1B (9.5 or something ?? ). 

When I connected the fuel gauge, to a Li-ion battery that I had - specs - 750mAh - ICR14500 ( http://www.amazon.com/2000mah-Rechargeable-Li-ion-Battery-Ultrafire/dp/B00BQYNC9U )   -   the uC on the board started heating up out of bounds so much so that I almost burnt my finger when I accidentally touched it. And this was before I had even connected my charger or any load across the corresponding pins. 

Is this normal ? Kindly help me diagnose the issue. 

Also, in a previous attempt without attaching the BIN pin resistor, I had attached the same battery to the gauge and operated bqStudio when it did detect the board and reported the battery voltage accurately. I clicked on the "Commands" set on the right tab, and clicked on all them, probably even "SHUTDOWN", "SEALED" etc. just to see what it did. I think after this point the gauge stopped communicating with the software. I later, tried running "UN-SEAL", "RESET" etc., but the communication didnt go through. After which I have had the heating problem. 

- Thanks and Regards, 

Chintan Pathak 

Scholar, 

University of Washington.

  • 0
    TI__Expert 3385 points
    Hi Chintan,

    bqStudio should automatically detect your evm when you connect it to your computer though the EV2400. You need to first connect the battery to the EVM, then connect it to your PC and open bqStudio. You should not have to manually go to gauges and find your device.

    Can you measure the battery voltage before connecting it to the EVM? Are connecting the battery positive to pack+ and negative to pack-?

    Also can you clarify what you mean the uC gets hot? Do you mean the fuel gauge IC itself gets hot?

    The 10-k resistor you see used on the bin pin to pack- set the BAT_DET bit, which will allow charge/discharge.

    Are you able to communicate with the gauge now via bqStudio?

    Best,
    Justin
  • 0 in reply to Justin Erfan
    Intellectual 845 points

    Hey Justin, 

    Sorry about the delay. Was just testing the system to make sure, I got everything right. 

    So apparently, the problem that bqStudio wasnt detecting the gauge, was that, I was using a totally discharged battery. It was a fresh battery and had no charge. I am currently in the process of charging it and will soon know how it behaves with our gauge. 

    Meanwhile, I used the gauge with a semi-charged battery, and made the connections as you had instructed, and voila....everything worked perfectly. The bqStudio (which I had re-installed, as a precaution) automatically detected the gauge upon startup and showed the values of the registers etc. 

    Also, the meat of the problem, the overheating (of the gauge IC, specifically the black spot in the middle), doesnt happen anymore. I dont know, exactly what was causing it, maybe I had sealed the battery and was getting the charge from the charger causing it to stagnate and cause heat. Anyway, lets hope it doesnt happen to anyone else. I am able to communicate with the gauge via bqStudio. 

    Havent understood what the 10-k resistor does and how to change the battery from charging to discharging, but lets leave that for another question.  :)

    Thanks, 

    Chintan Pathak 

  • 0 in reply to Chintan Pathak4
    TI__Expert 3385 points
    Hi Chintan,

    I am glad you were able to test these out. As for the 10k resistor, there is a bit called BAT_DET. This bit will be set if there is a battery detected in the system. This is a feature that we have for safety reasons. If this bit does not get set, you will not be able to charge and discharge.

    This bit gets set when the BIN (battery insert) pin is pulled low. However, we don't recommend pulling directly to ground; instead, we use this 10k resistor to pull low.

    The charger or load you will put across LOAD+/Charger+ and LOAD-/Charger- (using TP10 and TP7). If you pull a load, you will see a discharge current, if you use a charger, you will see a charge current. And remember you can only charge or discharge if you pull BIN low as described above.

    Best,
    Justin
  • 0 in reply to Justin Erfan
    Intellectual 845 points

    Hey Justin, 

    Thanks for the clarification. I think I get what the BAT_DET bit is for. Just to finish up though, by connecting the load, I can discharge my battery and by connecting the charger, I get to charge my battery.

    Is there a way charging and discharging can happen automatically ? As in, if I connect both, the load and charger and set the charging and discharging limits, can the gauge make my battery switch from charging mode to discharging mode on full charge and then from discharging mode to charging mode on min-voltage ?

    - CP