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BQ40Z50-R3-DEVICE-FW: BQ40Z50 R3 calibration issue

Steven(Shenzhen) Shi
Mastermind 30515 points
Part Number: BQ40Z50-R3-DEVICE-FW


Hi team,

After calibration when use BQ40Z50-R3, customer find the cell voltages have transient jump.

If they calibrate cell 1 to 4400mV. They will find 1mV jump for cell1 and cell2. 3mV for cell3. 4mV for cell4.

Please refer to the attachments.

They want to know below questions.

1. Why cell 3 and cell 4 have higher voltage jump?

2. How do we calibrate the cell voltage1-4.   -My reply: We only calibrate cell 1 voltage. And we use cell 1 voltage as a reference for cell 2&3&4 voltage. Is that correct?

3. How do we avoid this error? -My reply: We have maximum 13.1LSB nonlinearity for the ADC. We can't avoid this part of error by calibration. Is that correct?

BR,

Steven

NG1#.gg.csv

NG1#-4400mV 校准LOG数据.loghttps://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/NG1_2300_.srec

  • 0
    TI__Genius 11770 points

    Hello Steven,

    Can you confirm that the customer did calibration according to this document? I believe all of the internal ADCs should be identical. I could maybe see the VC1-GND being slightly different because it has a direct ground reference, but I don't think that can explain this. 

    Even though a difference of ~4mV is minor, it is still preventable. I believe if they re-do calibration according to the document they should be able to achieve better. Please confirm if they have done all of the calibration according to this guide. If so we can investigate further.

    thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    TI__Mastermind 30515 points

    Hi Alex,

    Customer never encountered same issues in their previous projects. They followed this instruction all the time. I think customer could accept this jump if we can give them a reasonable explanation about the source of this error and above questions. 

  • +1 in reply to Steven(Shenzhen) Shi
    TI__Guru** 105870 points

    Hello Steven,

    I took a look at the log, I'm not sure I understand the issue. It looks like the voltage is fluctuating around both the preset values (4400mV and 3700mV) Are they wondering why it's fluctuating more for the higher cell count? It may be due to the same gain being applied to all cells since it uses the same ADC. If they have a slightly noisy supply it may also cause some deviations.

    The gauge uses the same ADC for all voltage measurements, each value is muxed to get the cell reading. We apply the cell gain to the measurements which will be applied to all the cells.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    TI__Mastermind 30515 points

    Yes, they wonder why it's fluctuating more for the higher cell count. I agree with your point. And I think this noisy could be accumulated so the higher cell may have higher deviations? If they never encountered this issue before I think it most likely comes from their production line. 

    BR,

    Steven