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?

  • I think the same answer covers both of your posted questions (copied below)?

    If not, please let me know if I can help further.


    When /RESET is low (active), the part is in power-down mode. In this mode, the receive, transmit, and oscillator circuits are all switched off.

    The HART_OUT pin will hold at ~Vref/2 when in reset (so depends on the REF_EN pin and the voltage on Vref), while the RX pin won’t really change its input impedance from the ON mode. Aside from the internal ESD diodes to the supply and ground, the HART_IN pin goes straight to the internal filter.