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TPS745-Q1: functional safety question

Sherry Liang
Genius 10255 points
Part Number: TPS745-Q1
Other Parts Discussed in Thread: TPS745

Dear team,

My customer wants to know whether Config level can be changed. How to achieve >70% Config level?

Thanks & Best Regards,

Sherry

  • 0
    TI__Guru 50025 points

    Hi Sherry,

    I've sent a message to someone who might know more about this, but they are out of office until Tuesday. Please allow a few business days to get back to you.

    Thanks,

    Nick

  • 0
    TI__Guru 50025 points

    Hi Sherry,

    Here is what he said:

    For sample population with zero reliability fails the  70% CL FIT is 1.31x the 60% CL FIT .   

    The inverse chi square function in excel can be used to calculate the scaling factor to use to go from one known confidence level to another.  

     

    Scaling factor =  CHISQ.INV(70%,2) / CHISQ.INV(60%,2)  for sample population with zero fails

    So for this example, the 70% CL FIT is 0.2 * 1.31 = 0.26

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Genius 10255 points

    Hi Nick,

    Thanks for your help!

    I am not sure whether I understand your point, could you please help check whether my understanding is right? In my understanding, This scaling factor 1.31 is calculated by this formula, CHISQ.INV(70%,2) / CHISQ.INV(60%,2). If we want to increase the Config level, we need to increase the FIT value to 0.26 firstly. But I think the FIT value is fixed for specific device. How to increase the FIT value of TPS745?

    Thanks & Best Regards,

    Sherry

  • 0 in reply to Sherry Liang
    TI__Guru 50025 points

    Hi Sherry,

    The FIT rate is not really constant for a device. The way to interpret this is that for a given sample size, if we measured the FIT rate, with 60% confidence we will measure 0.2 or less, and with 70% confidence we will measure 0.26 or less. They can use the equation to approximate any other confidence level by scaling from the 60% confidence level as well.

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Genius 10255 points

    Hi Nick,

    Nick Butts said:
    The inverse chi square function in excel can be used to calculate the scaling factor to use to go from one known confidence level to another.  

    I don't find the inverse chi square function in excel. Could you please tell me where I can find it?

    Thanks & Best Regards,

    Sherry

  • +1 in reply to Sherry Liang
    TI__Guru 50025 points

    Hi Sherry,

    The inverse chi square function in Excel is as in the formula above: 

    CHISQ.INV(probability,deg_freedom)

     

    Regards,

    Nick