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ST RHF1401 AVCC Transient protection and Input Impedance

Question asked by tan.aysen on Oct 18, 2016
I am using STMicroelectronics' Rad-hard 14-bit 20 Msps A/D converter RHF1401 in one of my electronics boards. After analysis, I have discovered that my power supply to the AVCC (pins 41 and 42) may be susceptible to a transient of 5V for a duration of 20usec. In section 2.1, Table 3 of the datasheet for the RHF1401, the absolute maximum voltage rating for the AVCC is 3.3V. In normal operation, my power supply to the AVCC is comfortably below this absolute maximum. My questions for are thus:

1. Is a 5V transient for a duration of 20usec (microseconds) allowable input to the AVCC? 
2. If so, please explain the reasoning why (i.e. Is there a filter already built in?)
3. If not, what is the input impedance for the AVCC? Knowledge of the input impedance can allow me to design an RC filter for my power supply into the AVCC to filter the transient.

Thank you in advance.