Post Go back to editing

Question about over of TME velue in Normal mode at Cell 1 & Cell 15

Category: Hardware
Product Number: LTC6813HLWE01#3ZZTRPBF

Hello,

My customer use LTC6813-1 in their system and 15 Cell is used only.

And at thehis system, they found 15S BMS dara error.

As the spec. in Datasheet, max. value of TME in Normal mode is Max. ±3.3mV.

But when they measured Cell1 & Cell15, Cell 1  is 4.4mV and Cell 15 is 6.6mV.

Other cells are in ±3.3mV. 

Q1) Would you share your opinions why value of Cell 1 & Cell 15 are over Max. ±3.3mV which value is a spec. in datasheet?

Q2) Would you check their schematic in 4 page of attached file?

Q3) Would you check a test procedure and test result in 2, 3 Page of attached file?

Please advise me.

Regards,

Se-woong

PDF

PDF

Top Replies

  • Hello,

    My customer is waiting your answers.

    And they want to get your answer by this friday.

    Please confirm their issues and let me know your opinions ASAP.

    Regards,

    Se-woong

  • Hello Se-woong,

    Can you please ask them to check the TME results in one frequency mode lower i.e, either in 1KHz mode or 422Hz mode, and report if they see any differences. 

  • Dear SideshS

    They sent their test file at 1KHz.

    But the result is not good.

    Please refer attached file and let me know your advice ASAP.

    Regards,

    Se-woong

    PDF

  • Dear SideshS

    Would you let me know your status about this issue?

    My customer still need your help.

    Please let me know your opinions ASAP.

    Regards,

    Se-woong

  • Dear SideshS

    I still need your help.

    My customer is waiting your answer over 2 weeks.

    Please help me.

    Regards,

    Se-woong

  • Hello Se-woong,

    Apologies for the delayed response.

    Considering that there's no significant difference in the TME results obtained in one frequency lower and TME failing only in the Top and bottom cells of the Stack, it could be that they are not synchronizing the external DMM measurement timing with the timing at which the LTC6813 measures after we send a conversion command.

    It could be that they start the external DMM measurement immediately after sending the conversion command but since the V+ and V- of the LTC6813 are connected to the C15 and C0 lines of the Stack respectively, the change in V+ current between the time they measured in external DMM and the time at which LTC6813 samples and does conversion should be the cause for the TME failing in only top and bottom channels.

    Synchronizing the external DMM measurement with the device measurement should resolve the issue. And also they should take multiple consecutive measurements and average the results they obtained from their external DMM if their DMM can convert faster than LTC6813. 

    To precisely predict when the LTC6813 will measure a particular channel after the Conversion command please refer Measuring Cell Voltages (ADCV Command) subsection(specifically Figure-3 and Table-5) under the ADC Operation section in Datasheet.

  • Dear SideshS,

    Thank you for your kind answer.

    They ask some questions about the external DMM in your answer.

    Please refer below questions and let me know your opinions.

    Q1) What is the meaning of the external DMM? 

    Q2) How to  measure timming with the external DMM?

    Q3) Would you suggest your recommended DMM for this measurement?

    Please advise me.

    regards,

    Se-woong

  • Q1) What is the meaning of the external DMM? 

    Through DMM, I was referring to the external instrument they should have used to measure the voltage at the FPCB point(i.e, at points 2 and 4 as depicted in the document you shared). I assumed it to be a Benchtop Digital Multimeter (DMM).

    Q2) How to  measure timming with the external DMM?

    You should synchronize the time when the Conversion command is sent and the time when polling ends with the start and stop of continuous conversions in the external instrument used for the measurement. Then use the info in the datasheet to find the set of data from the external instrument that corresponds to conversion during the time when the device was also converting that particular channel. And then do an average of the data obtained and use that to check the TME. 

    Q3) Would you suggest your recommended DMM for this measurement?

    Any Calibrated Benchtop Multimeter with 6.5 digits or more resolution should work.