S32K324 FuSa Questions from the Customer

[WeoWang]

Hi Dear Colleagues,

My customer has some FuSa questions about S32K3:

If V25/V15/V11 is shorted to GND, is SM3_PMR_MON necessary? Why Single Point Failures of V15/V11 don't affect the safety goal?

[ehtesham_khan]

Hello Weo Wang,

Please find the answer to your questions below:

1. If V25/V15/V11 is shorted to GND, is SM3_PMR_MON necessary?

The V25 and V11 are internally generated voltages from VDD_Hv_A that will be used in different IPs such as cores, flash etc. SM3.PWR_MON is required for V15 pins. It is not required for V25 and V11 pins.

2.  Why Single Point Failures of V15/V11 don't affect the safety goal?

There are multiple V15 and V11 pins available, which are redundant. Loosing one is normally not a problem since there is some operational margin.(Loosing many will cause throttling of the regulators and it is notified by corresponding LVR). So there should be more than a single fault to occur to violate the safety goal, therefore we have considered it as a multiple point failure.

Hope this clarifies your doubt

-Regards,

Ehtesham

[FXY]

Single Point Failures for V15 and V11 pins should include both open and short.

I think the open circuit of V15 and V11 pins can be regarded as multi-point, and the redundant safety mechanism can be used, but short to GND is not suitable, because the hardware schematic design is in a short-circuited state outside the chip, as shown below, V15 and V11 pins share a set of capacitors and networks respectively.

So, to avoid Single Point Failures on V15 and V11 pins, what is NXP's recommended schematic design?
1. Need to consider circuit isolation in schematic design between pins?
2. External monitoring?
3. Other recommended security mechanisms?

[nxf55526]

Hello Kevin,

'Short to GND' here refers to the short between the V15/V11 pin and the VSS pin which is the ground pin in the package and could get shorted to V15/V11 pins. V15 power supply is being monitored externally and the short of this pin to GND would get detected by the external monitoring, while the short of V11 pin to GND would get detected by the internal voltage monitors present in the chip.

Hope this clarifies the doubt. 

Kind Regards,

Avni