Hello,
FM218 is about a failure in voltage monitors of the "main" supplies and biasing.
The assumption is the failure in this monitor will prevent the fault to be detected in this "main" area.
We could then imagine a fault in the "main" biasing circuitry can't be detected due to this latent fault; however the VR5510 architecture offers a fully independent Failsafe monitoring module that will detect in any case a possible cascaded effect (wrong regulation on the voltage rails, violation of safety goal) of the fault in the "main" biasing.
This is why we wrote this rationale that the possible effect of latent fault + fault in "main" biasing will be detected by the failsafe monitoring module with the SM20.
I hope it helps clarifying the point.
our best regards,
