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OPA350 reverse breakdown

Alberto Biancalana
Intellectual 380 points
Other Parts Discussed in Thread: OPA350

Hi,

I'm looking at an Op Amp design where and OPA350 is working in a not inverting configuration, driven by a piezo ceramic. The piezo throughput must be bidirectional, so, when on TX, an high level signal is brought to the piezo and the OPA350 positive input is protected by a couple of end to end diodes that limit the signal at +-1V  max.

I know that bipolar OpAmp input are very sensitive to reverse breakdown current but this is a CMOS, so the question is simple and probably obvious for people more expert than me: should I worry about damage to the OPA350 in this configuration?

Thanks, any help is appreciated.

Alberto

  • 0
    TI__Genius 12345 points

    Alberto,

    The inputs of the OPA350 have protection diodes which clamp the input voltages to approximately .3V beyond either supply rail. Therefore, if you apply -1V to either of the inputs when the negative supply of the OPA350 is connected to ground, you will forward bias one of the on-chip protection diodes and cause an excessive amount of current to flow out of the input, most likely damaging the OPA350 in the process. The solution is to place a resistor in series with the non-inverting input of the OPA350 to limit the current flowing into or out of the input when a voltage outside of the acceptable voltage range is applied. The absolute maximum current rating for the inputs of the OPA350 is 10mA, thus the series resistor MUST be larger than 1V-.3V / 10mA = 70 Ohms. I would chose a much larger value than this just to be on the safe side.

  • 0 in reply to John Caldwell
    Intellectual 380 points

    Thank You John,

    this has been very useful to me.

    Regards

    Alberto