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ISO121: If input power supplies are down, output goes high

Michael Marchant
Prodigy 20 points
Part Number: ISO121
Other Parts Discussed in Thread: ISO224,

We can have a case where the +/- 5V power supplies are off on the input side.  The input pin is grounded.  The output side power supplies are on at +/- 5V.  The output goes out of control towards the + rail.  Is there some known way of dealing with this?  Ideally, we would want zero on the output.

  • 0
    TI__Guru**** 176181 points

    Hi there and welcome to our e2e forum!

    Unfortunately, with no power applied to +/- VS1 on the ISO121, we can't guarantee what the output voltage is going to be. We do have a newer isolation amplifier that you might consider - the ISO224, which has a fail-safe output voltage that is 0V differential while the high side supply is missing, so this may be a potential solution for you.

  • 0 in reply to Tom Hendrick
    Prodigy 20 points
    ISO121 is the only amplifier that has a working voltage high enough for our application. We will just have to take extra measures to identify and protect against the errant output when it happens.