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Inputs to ADuM6211 when un-powered

I would like to use the ADuM6211 to isolate an incoming external digital trigger (very low speed, ~1Hz).  The trigger will be a 0 to 3.3V signal but I would like to protect against over-voltage (up to 10V) and reverse polarity.  I'm planning to implement this protection with a series resistor (10K) from the ext trigger to the VIA input and 2 Schottky diodes on VIA (1 to VDD2/Viso, 1 to GNDiso).  There will also be a 10k Ohm pull-up resistor on the external trigger input connecting it to VDD2/Viso.  I believe this should protect the ADuM6211 while it is powered on, but I would also like to protect it in case an external signal is applied while the ADuM6211 is powered-off (No voltage on VDDP/VDD1).  Is it OK if Viso/VDD2 is "powered" through the pull-up resistor when VDDP/VDD1 is un-powered?  If so, what limits of voltage / current can be applied without damage.

  • Suluclac:

    The ADuM6211 can be protected with the 10k resistors in the circuit you described if arranged correctly with the schottky diodes.

    The absolute max voltage of the VISO & VDD2 pins is 7.0V, so the circuit needs to be less than this, where 5.5V is the normal operating voltage. The current into VIA needs to be < 1mA continuous current to protect internal ESD diodes on VIA.

    Regards, Brian