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BQ20Z40-R1: Static Chem DF Signature Consistency

Steve Patterson
Intellectual 570 points
Part Number: BQ20Z40-R1
Other Parts Discussed in Thread: BQSTUDIO, BQEVSW, , BQ40Z50-R1

I have a battery pack from the first lot the vendor shipped to us, and one from the second lot (which were programmed with the wrong Chem ID).  I reprogrammed both with the correct Chem ID and also with our “golden” parameter file with the following filter:  all parameters were programmed (including calibration) except not the Ra Table.  I assumed the default Ra Table was as good or better than what we have in our “golden” parameter file.  After doing this, I expected the Static Chem DF Signatures to be identical, but lot 2 was C362 hex and lot 1 was 4362 hex.  They’re close, which is suspicious, but not the same.  Can TI shed some light on this?  The only difference between the packs that I’m aware of is lot 1 has 2 thermistors where lot 2 only has 1.  Thanks for any help on this mystery.  I'm using BQ Studio 1.3.76 (the "test" version).

  • 0
    TI__Guru* 76230 points
    hi Steve,
    Are you sure you are using bq20z40-R1 because those older legacy devices use bqEVSW not bqstudio.

    With regards to the static chem checksum, that should differ if you have different chem ids or if your chem id didn't successfully program. For checksum c362, it appears the MSB is set to 1 , i.e C= 1100. This means the checksum in your dataflash is differnt from the check sum the gauge is calculating.
    If indeed you are using bqstudio, there should a static checksum command button. Click it, and what ever result you get write that in the static checksum section of your data flash. I am assuming the correct checksum would be 4362
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 570 points

    I must have entered the wrong device - it's a BQ40Z50-R1. 

    So the signature is 15 bits and the MSB is the check result?  That would explain the similarities in the signatures.  So does the chip compare the calculated signature to the value in the DF?  The DF value is 0 in the parameter file at this point in time, but in both chips so I would expect the same result (C362).  TI said that the DF value is never changed by the chip, only by the user.  I'll check the values and see if the results make sense.  Thanks for your response!

  • 0 in reply to Steve Patterson
    TI__Guru* 76230 points
    Yes the MSB is the check result. If that is set to 1, it usually means there is a mismatch between what the gauge calculated and what is written in data flash.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 570 points
    Thanks Onyx. One of the batteries I programmed didn't get the Static Chem signature parameter updated. More likely the entire write failed, but gave no error message. I've seen this before where the file write looks like it happened but didn't. I thought that was due to the masks BQ Studio applies, but I now know about displaying advanced options so I set the masks and the System Data writes were definitely enabled. I'll add a check step after programming to catch this if it happens again. Thanks again for the answer.