question about FMEDA of 33771&33772

[Chenlong_Wu]

Regarding the FMEDA of 33771&33772, I have a question on OC’s ASIL level.

before information is that with/without use SM39(Use of AN5 and AN6 as Current Measurement input), the ASIL level of OC shall be C and B.

but I found in each FMEDA, 771B/771C/772B will change from D to B when disable SM39

772C will change from D to C when disable SM39

Do you know why 772C can reach ASIL C without use SM39?

And if our FMEDA consider external filter circuit?

[SavinoLupo]

Hi Chenlong Wu,

thank you for the excellent question.

It took me time to check. I saw the customization of the MC33771C calculation has a problem like the one found in the MC33772C Excel file, which was corrected. I attach the new version of the work MC33771C FMEDA, which will be uploaded to nxp.com. You will see the issue is solved, the result after the customization is ASIL C.

Regards,

Savino

[Chenlong_Wu]

Hello @SavinoLupo 

got the information of 33771C, and thank you for your quickly answer.

How about the B version?

In my opinion, there are no different between B version and C version on Current function.

if B version still only meet ASIL B without SM39,  and why?

thanks!

Chenlong

[SavinoLupo]

However, keep in mind that the FMEDA result is at IC level, it gives no guarantee that ASIL C is met at system level, because the absence of the double filter will not allow to easily detect failure modes on the filter sitting on the PCB.

[TomasVaverka]

Hi,

I have asked our BMS Safety Expert and author of the Safety Manual/FMEDA to answer this question.

BRs, Tomas