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In FMEDA should I consider both permanents Failure and transient Failure?

Question asked by Davide Masi on Oct 10, 2019


I'm developing the FMEDA of a system that integrates the MPC5744P - Panther uP.
I'm using the metrics provided by the FMEDA Summary (I filled the Excel customer and the FAE provided me the FMEDA summary)

I remember that the metrics of Failure FMEDA Summary = permanents Failure + Transient Failure 


In my FMEDA I should consider both? Permanent and transient?


The doubt arises because the SRAM is described by "2700 FIT (summary) = 1 FIT (permanent) + 2699 FIT (transient)" but I use all SM available to mitigate the failure (ECC, MBIST, LBIST,...).


Futhemore the SRAM customer file has a sheet called "Module FMEDA" that describes Soft Errors

In this sheet the SM called ECC, can control Soft errors with 100% coverage (controlled DC=100%, detected DC=0%)


controlled = corrected but not detected
transient failure  = temporary event


In FMEDA should I consider both permanents Failure and transient Failure?

What is the correct methodology for treating transient Failure in functional safety?