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TL084: Quality data at 70% confidence level

Part Number: TL084

Hi expert,

My customer is doing functional safety related analysis and may need quality data with 70% confidence level. But most data we direstly get from TI website is 60% confidence level. Could you take TL084 as an example on how to directly or indirectly get this data?

Thanks

Sheldon

  • Hello Sheldon,

    Do you need an explanation or a formula to calculate the confidence level given here?

    If so, I am not sure how this number is calculated.  However, I will reach out to the individuals that are responsible for this and get back to you ASAP.

    Regards,

    Daniel

  • Hello Daniel,

    I didn't get much explanation on what is "confidence level" here, also, I am not that good at statistics. Hope you can help me further investigating on how the "60% confidence level" is got or how can I get data at "700% confidence level".

    Thanks

    Sheldon

  • Hi Sheldon,

    here is a good explanation:

    spraby3.pdf

    And we have discussed the Arrhenius formula here, e.g.:

    Kai

  • Hi Kai,

    I thinks we are close the answer. The document mentioned a spread sheet which is what I need, But on the website, when I click on the "download spreadsheet" I will not get a excel. Could you help me with that? Let's take TL084 as an example. Thanks!


  • Hi Kai,

    I thinks we are close the answer. The document mentioned a spread sheet which is what I need, But on the website, when I click on the "download spreadsheet" I will not get a excel. Could you help me with that? Let's take TL084 as an example. Thanks!


  • Hello Sheldon, 

    The document Kai referenced does point to a spreadsheet which is unfortunately unavailable via the website. Let me see if I can explain the steps needed to complete the calculation manually: 

    1) Calculate AF factor using equation 1 below. 

     Eq. 1

    2) Plug calculated AF and additional parameters into equation 2 below.

     Eq 2

    • You'll recognize the formula from TI article Kai shared. I manually put brackets around the chi-squared value (this is a single term!), since the formatting of this expression is terrible. Your %CL value is 0.7 (for 70% confidence interval) whereas f (# of failures) is 1 for TL084 specifically. You can calculate the chi-squared value here:

    https://keisan.casio.com/exec/system/1180573197

    Select 'upper Q', use 0.7 as 'cumulative distribution' value, and use 2*1 + 2 = 4 as 'degrees of freedom'. This will give you chi-squared of ~0.71 for confidence interval of 70% with 1 failure (applicable to what you're looking for). 

    • Remaining values (t, ss, f, etc.) you'll need for equation 2 can be found on the DPPM/FIT/MTBF estimator page for TL084 under 'MTBF / FIT supporting data':

    https://www.ti.com/quality/docs/estimator.tsp?OPN=TL084QDR&CPN=&partNumber=TL084#resultstable

    Voila! That should allow you to calculate FIT rate at any desired confidence level. 

    Please let me know if you have further questions. 

    Regards,
    Vladimir

  • Sheldon,

    It looks like Vlad's post should answer your question.

    Please let us know if you need any further assistance.

    Regards,

    Daniel