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BQ34Z100-G1: Board offset not being applied

Jeffrey Wright
Expert 2855 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ76952, BQ34Z100, BQSTUDIO

Hello;

My client's BMS uses the new bq76952 Monitor/Protector and the bq34z100 fuel gauge. Both measure the sense resistor. Both are calibrated for board offset and CC gain/offset. However, while the 952 correctly applies this board offset to its reported current measurement, the 34z100 appears not to do so. After calibration, the 76952 reports 0 to 1mA of current when there's no current flowing, but the 34z100 reports -49mA, both before and after calibration.

 Both the host u/C's calibration routine and bqStudio's calibration procedures produce the same results. After board offset calibration, the gauge should report the same as the 952, or very close to 0mA.

Since I cannot find any errata sheet for the gauge, this would appear an issue.

What could cause this? Or what am I missing?

  • 0
    TI__Guru** 102415 points

    Hello Jeffrey,

    I got the same behavior while applying a constant current to the gauge and trying to calibrate the offset, let me check with the firmware team if there's something that needs to be updated. I tested with 50mA as well, but the offset may be too high, this is the only reason I could see it would fail without there being some other issue.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Expert 2855 points

    Ok, thanks Wyatt.  While you're checking with the F/W team, please also ask about the very long offset calibration time (it takes ~38 seconds on my boards). The other gauges and protectors I've used (78350, 76952, etc) take only 3 or 4 seconds, and the 34z100 takes just a few seconds for CC gain cal.

    THanks!

  • 0 in reply to Jeffrey Wright
    TI__Guru** 102415 points

    Hello Jeffrey,

    I'm waiting to hear back from the FW team, hopefully will hear back later today or tomorrow.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    TI__Guru** 102415 points

    Hello Jeffrey,

    I've been talking with our FW team, he made the comment that 49mA is very high and is mentioned it may be leakage current. I tried testing with lower currents but it doesn't seem to correct anything using bqStudio.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Expert 2855 points

    I agree that 49mA is a high offset, but since the 76952 will calibrate it out, the 34z should as well. Is it possible that the offset calibration routine in the 34z is just rejecting the offset because it's out of a max defined range? If so, bqStudio doesn't  report this, and if fact returns a green checkmark indicating it completed a successful calibration.

    Please continue to dig for answers from your F/W people

    Thanks 

  • 0 in reply to Jeffrey Wright
    Expert 2855 points

    Hello Wyatt;

    FYI...We've tested the offset cal. with a smaller offset of ~13mA, and the gauge still does not apply it to the reported current. From one of my client's engineers:

    "I can confirm that I am seeing the same thing as Jeff on BQStudio with regards to the current offset. Both boards I used had 0 offset out of the box but I connected a load to introduce a small offset of about 13 mA. I then checked to calibrate the CC offset and calibrate the board offset. The BQStudio program returned a green check mark as if it successfully completed the calibration but current gauge still did not zero out the small current offset."

    Let me know asap what your F/W people find. (and don't forget about the very long board offset cal time as well)

    Thanks

  • 0 in reply to Jeffrey Wright
    TI__Guru** 102415 points

    Hello Jeffrey,

    I have been testing it as well with different currents and methods, but it will not zero the current.

    I filed a ticket internally for it to be fixed.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Expert 2855 points

    Ok, thanks Wyatt;

    I'm guessing that any fix wouldn't be available for quite a while, so my client may have to deal with this issue.

    And again, while the offset issue is being corrected by your F/W people, please have them also check into the very long offset calibration time...40 seconds is just way too long.

    Thanks!

  • 0 in reply to Jeffrey Wright
    TI__Guru** 102415 points

    Hello Jeffrey,

    I'll let you know any updates if were able to get it out quicker.

    Sincerely,

    Wyatt Keller