AD5700/AD5700-1 Input Z to HART_IN Pin?

I'm not finding any input specification (or application examples) for the HART_IN pin that implies its input z and/or bias current requirements.  Specifically, I'm wanting to use the part's internal filter option and am undecided how to apply protection without knowing the latitude I have to add external series limiting.  My supply rail will be 3.3V when powered-up or 0V when powered off (hence my question re. Rx/Tx loading when the part is not powered).  Suggestions?