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Original question:

SN751177: DPPM/FIT/MTBF estimator & Temperature Change FIT

SN751177: FIT estimator procedure

Toshihiro Watanabe
Genius 10235 points
Part Number: SN751177


Hello,

I still can't fully understand how to use FIT calculator. There are three input items, app temp, Qual temp, DPPM as below.

App temp is to select our ambient temp to input.

I guess Qual temp  is below Test temp, 125C. Is my understanding correct?

What number should we put in DPPM? above ELFR-DPPM or use DPPM sample size caluculator?

Please let me one more question. Conf level is 60% is used. There is also 90%. Is 60% moderate number for calculating FIT? What is 90% for?

Best regards,

Toshihiro Watanabe

  • 0
    TI__Guru 62920 points
    Hello Watanabe-san,

    For your first question about the temperature change FIT calculator, you should use the data marked "Early life failure rate supporting data." In this case that would mean the qualification temperature is 125 C and the DPPM is 56.

    For your second question on the DPPM estimator - this tool can be used with any data set, and just performs the statistical analysis needed to extrapolate the number of fails at a given sample size to the number of fails per million units at a given confidence interval (i.e., using a chi-square distribution function). If you use the ELFR-DPPM data for this you get the ELFR-DPPM value reported in the device's reliability table (in this case, 56). If you use the MTBF/FIT supporting data, then you would estimate the DPPM per 1000 hours of operation.

    Does this make more sense now? Please let me know if you have further questions.

    Regards,
    Max Robertson