Q
Truthtable in datasheet of ADuM524x Rev.A page 9 says that the output is in
"Z"-State, when Viso State is unpowered. We have a problem, that VOB is
influencing other functions in our design although pin should be "Z". How is
"Z" defined? What impedance of the output can we expect?
A
When there is no power, the high and low channels are both off... so the
output buffer is off in both directions giving a high impedance.
Unfortunately since there are ESD diode structures on I/O pins....If the
voltage at a pin is pulled up from an external source, then once the ESD diode
is forward biased, it will conduct and not look like a high impedence any
longer. So it's impedance curve will look like a diode to Viso or Vdd. The Z
really represents a floating output between the protection diodes. It can not
be treated as a high impedance independent of applied voltage.