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BQ79606A-Q1: The effect of SM711: Die Temperature versus PTAT Sensor Accuracy Measurement Failure

Zizhen Yu
Prodigy 120 points
Part Number: BQ79606A-Q1

Dear Mr. Mrs

When implement the SM711, I want to know the effect if SM711 test failure?

According to safety manual, SM771 failure just a MPF?

If SM711 failure, it will have impact on cell voltage measurement? on cell temperature measurement? on cell voltage protection function? on cell temperature protection function?

Do you have a recommend threshold value for SM711(the mismatch between the PTAT voltage and the DIE_TEMP)?

In addition. I also want to know the effect if SM132: VC and CB Pin Short Check failure.

for example:

  1. if VC5 and CB5 short, I think it will have no impact on cell voltage measurement if the cell balance inactive. right?
  2. if CB5 and VC6 short, I think it will have a big impact on cell voltage measurement. right? 

Thankyou!

  • 0
    TI__Mastermind 23410 points

    Hi Zizhen,

    SM711 reports if the IC is operating above or below 115C or 125C. When it fails, the device is operating well above 105C which is where most of the ADC measurement accuracies are specified at. We cannot guarantee proper functionality when operating outside of the Electrical Characteristics. 

    We specify this as a latent fault coverage. 

    For a recommended threshold, this is only what you are comfortable with. I cannot dictate the range of deviation that you are ok with between the PTAT reading and the DIE temp reading. 

    Zizhen Yu said:

    I also want to know the effect if SM132: VC and CB Pin Short Check failure.

    for example:

    1. if VC5 and CB5 short, I think it will have no impact on cell voltage measurement if the cell balance inactive. right?
    2. if CB5 and VC6 short, I think it will have a big impact on cell voltage measurement. right? 

    Agree for both statements. I will let you know if I find anything that says otherwise. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 120 points

    Hi Anthony

    Thank you for your answers.

    But the description of SM711 in safety manual as shown in below picture, it only detect the mismatch between the PTAT voltage and the DIE_TEMP. I think SM711 will not reports if the IC is operating above or below 115C or 125C. Or there may be some other way to report the fault if the IC is operating above or below 115C or 125C.

  • 0 in reply to Zizhen Yu
    TI__Mastermind 23410 points

    Yes Zizhen,

    When the test fails, it is in an indication of deviation from measuring the temperature. This is where it is to user design descretion how to much variation you are allowing in your system. 

    Best Regards,

    Anthony Pham