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ISO7041: Working RMS vs lifetime calculation

Jimmy Palmer
Prodigy 80 points
Part Number: ISO7041
I would like to use the ISO7041 or ISO7041-Q1 to send gate drive signals to high-side device in a half-bridge in an automotive application. However, the data sheet states a working voltage of only 400Vrms and I may have a working voltage of ~450Vrms. I'm trying to use the following table in the ISO7041-Q1 data sheet to arrive at the expected lifetime given a 450Vrms working voltage. 
Example:
I have a lifetime requirement of 100 years. I need a 20% safety margin for working voltage and 87.5% safety margin for insulation lifetime. Based on this, the maximum working voltage I could use with the ISO7041-Q1 is ~ 1280Vrms. I know I did the math backwards there, but is that how the chart is meant to be used?
100y *1.875 = 187.5y
-> 187.5y = 5.913e9 secs
Vrms @ 5.9e9 secs = 1600Vrms
1600Vrms/ 80% = 1280Vrms
  • 0
    TI__Genius 11275 points

    Hi Jimmy,

    Your calculation method for the graph is correct but we don't recommend to use the device outside its data sheet max limits as TI can't guarantee the device performance in such cases. The working voltage is typically limited to a lower value due to smaller package size and many applications have other limitations such as Creepage distance, reinforced vs basic insulation, etc.

    That said, since your required voltage is 450 Vrms, which is only marginally above 400 Vrms, I don't foresee any issues and the device should be able to sustain this stress.

    Thanks,
    Saleem Marwat