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BQ79606A-Q1: The question about using FMEDA calculate tool

Zizhen Yu
Prodigy 120 points
Part Number: BQ79606A-Q1

Dear Mr. Mrs.

 About BQ79606 FMEDA calculate tool, we have some questions need your help:      

  1. “Life Cycle” in <Mission Profile Tailoring>. Our project’s life cycle is very special, it need 15 years but active operating time is 27550 hours. So does the life cycle in the FMEDA tool can be modified according to our requirements?
  2. The operational profile in <Mission Profile Tailoring> is based on IEC/TR 62380, can you provide a SN29500 version?
  3. Whether this FMEDA calculate tool only for cell voltage monitoring and temperature monitoring, i.e. SG1 and SG2. If we want to calculate the FMEDA for SG3 and SG4, i.e. Cell Voltage Protection and Temperature Protection., Do we need to use a new FMEDA calculate tool?
  4. About <Pin Level Tailoring> in the FMEDA calculate tool, we just need to select whether the corresponding failure mode of every Pin is safety related or not, i.e Column G? Do we need to select the corresponding safety mechanism, i.e Column N? because in this table, the corresponding safety mechanism has been selected. If we want to select a another safety mechanism for a specific failure mode,  Do we need to analyze the applicability and coverage of this mechanism?

  1. About <Function and Diag Tailoring> in the FMEDA calculate tool. We are not very clear about the effect of sub-circuit block's failure mode for Safety Goal or chip level system function. Does TI has some document or  materials to introduce these failure mode's system level effect and the function definition of every part?

The following picture is the FMEDA calculate tool we used.

  • 0
    Prodigy 120 points

    The 1st picture should be this one, sorry for this mistake.

  • 0
    Prodigy 120 points

    Add a new question:

    The AVSS pins are used to connect GND, and the AVSS is the reference ground for measurement. So I want to confirm whether the AVSS pin is related to safety function? And whether the AVSS pin open failure is a safety related failure mode?

    In BQ79606, there are two AVSS pins, AVSS_15 and AVSS_45. But their function seem isn't same. The AVSS_15 and AVSS_45's open failure not have any safety mechanism to cover. If I select "Yes" to set AVSS' open failure are related to safety function, but have no corresponding safety mechanism to cover them, it will cause the SPFM drop too much to 92.17%. So I want to know how to deal with this situation.

  • 0 in reply to Zizhen Yu
    TI__Expert 7000 points

    Hi Zizhen,

    I will be able to provide an answer to this E2E tomorrow (3/22).

    David

  • 0 in reply to David Ray
    TI__Expert 7000 points

    Hi Zizhen,

    As these are a lot of questions in one E2E, and our FMEDA team is a bit backlogged at the moment, they will be able to provide answers to these questions next week.

    Regards,

    David

  • 0 in reply to David Ray
    Prodigy 120 points

    Hi David

    Do you have a guild line to introduce how to use the FMEDA calculation tool? It would be very hopeful.

    And can you give us a more accurate time when you can provide answers.

    Thank you!

  • 0 in reply to Zizhen Yu
    TI__Expert 7000 points

    Hi Zizhen, 

    Our FMEDA team said that they will be able to respond to give some answers to this topic tomorrow.

    Regards,

    David

  • +1 in reply to David Ray
    TI__Expert 7000 points

    Hi Zizhen,

    Zizhen Yu said:
    “Life Cycle” in <Mission Profile Tailoring>. Our project’s life cycle is very special, it need 15 years but active operating time is 27550 hours. So does the life cycle in the FMEDA tool can be modified according to our requirements?
      1. Yes, you can modify this on the “Mission Profile Tailoring” tab. Tau(on) and Tau(off) are calculated from the values listed in t1, t2, t3, which is the power on time at each of the 3 temps. If you take the 27550 hours which is 0.20967 of 15 years and split it across the temps, you will have the total active time.
    Zizhen Yu said:
    The operational profile in <Mission Profile Tailoring> is based on IEC/TR 62380, can you provide a SN29500 version?

    This will be generated and should be available by the end of this week (3/29).

    Zizhen Yu said:
    Whether this FMEDA calculate tool only for cell voltage monitoring and temperature monitoring, i.e. SG1 and SG2. If we want to calculate the FMEDA for SG3 and SG4, i.e. Cell Voltage Protection and Temperature Protection., Do we need to use a new FMEDA calculate tool?

    Currently, the FMEDA will need to be modified to allow SG3 and SG4. This modification may take up to the end of next week (4/5).

    Zizhen Yu said:
    1. About <Pin Level Tailoring> in the FMEDA calculate tool, we just need to select whether the corresponding failure mode of every Pin is safety related or not, i.e Column G? Do we need to select the corresponding safety mechanism, i.e Column N? because in this table, the corresponding safety mechanism has been selected. If we want to select a another safety mechanism for a specific failure mode,  Do we need to analyze the applicability and coverage of this mechanism?

    If a pin is not safety related for your application, you can change the value in column G. The safety mechanism that is selected is the appropriate one for each pin. If you would like to use some other safety mechanism, or a user defined external mechanism, you would have to determine applicability and coverage.

    Zizhen Yu said:
    About <Function and Diag Tailoring> in the FMEDA calculate tool. We are not very clear about the effect of sub-circuit block's failure mode for Safety Goal or chip level system function. Does TI has some document or  materials to introduce these failure mode's system level effect and the function definition of every part?

    The circuit block description provides some information, and the Datasheet should also describe the blocks.  The sub-circuit failure mode association to SG is not part of the spreadsheet. In subsequent generations of BQ devices we are starting to generate that information.

    Zizhen Yu said:

    The AVSS pins are used to connect GND, and the AVSS is the reference ground for measurement. So I want to confirm whether the AVSS pin is related to safety function? And whether the AVSS pin open failure is a safety related failure mode?

    In BQ79606, there are two AVSS pins, AVSS_15 and AVSS_45. But their function seem isn't same. The AVSS_15 and AVSS_45's open failure not have any safety mechanism to cover. If I select "Yes" to set AVSS' open failure are related to safety function, but have no corresponding safety mechanism to cover them, it will cause the SPFM drop too much to 92.17%. So I want to know how to deal with this situation.

    DVSS and CVSS are considered safety related and have GND open checks (SM24 and SM34). They are connected to AVSS so the loss of pin connections for the 2 AVSS pins are not considered safety related.

    Regards,

    David

  • 0 in reply to David Ray
    Prodigy 120 points

    Hi David:

    Thank you for your answers. they almost resoled my questions.

    About the answers:

    David Ray said:
    This will be generated and should be available by the end of this week (3/29).

    After you have generated SN29500 version FMEDA calculation tool, can you send it to my E-mail(zizhen.yu@preh.cn) or add it into my TI account(zizhen.yu@preh.cn).

    David Ray said:
    Currently, the FMEDA will need to be modified to allow SG3 and SG4. This modification may take up to the end of next week (4/5).

    The time is OK for us. Also, can you send it to me in the same way as above?

    David Ray said:
    DVSS and CVSS are considered safety related and have GND open checks (SM24 and SM34). They are connected to AVSS so the loss of pin connections for the 2 AVSS pins are not considered safety related.

    If we only use SM34 DVSS open check, but not use SM24 CVSS open check, is it OK and enough for VSS open check? because we only use one pcs BQ79606 in ECU, and use UART to communication, so the CVSS related SMs have been tailored.

  • 0 in reply to David Ray
    Prodigy 120 points

    Hi David：

    Because we only use one pcs BQ79606 in ECU, and use UART to communication, so some not related SMs have been tailored.

    I am hoping you could help determine if these failure modes are not safety-related or can be covered by other SMs and how to deal with these situation

    1. Sub-circuit block: A4_IREF, Failure mode: LDO_VLDO ref current offset......Because we only use one pcs BQ79606 in ECU, and use UART to communication. So this failure mode is not safety-related, OK?
    2. Sub-circuit block: A4_IREF, Failure mode: VIF ref current offset.....Same with "1". So this failure mode is not safety-related, OK?
    3. Sub-circuit block: H11_CLK_CTRL, Failure mode: HFO frequency div for digital core fault / Reset digital core fails to trip / UART clock output fault.......These failure modes are covered by SM500&SM502&SM508&SM509~SM513. But SM509~SM513 have been tailored due to the means of communication. So these failure mode can be covered by other SMs?
    4. Sub-circuit block: K1_OSC_32M, Failure mode: Drift of output frequency / Incorrect frequency fast>10% / Incorrect frequency slow>10%......These failure modes are covered by SM500&SM502&SM508&SM509~SM513&SM720. But SM509~SM513 have been tailored due to the means of communication. So these failure mode can be covered by other SMs? such as SM721?

    Thank you!