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Op Amp power increase with amplitude

Other Parts Discussed in Thread: TLV2381

I have been asked to answer this question for a co-worker of mine. We have a circuit that is basically a mic pre-amp/filter. It consist of a INA and a couple TLV2381's. All ICs are operating at +/- 3.3V. The normal operating current draw for the board is .225mA, but when sound is detected by the passive mic the current can jump up to 2mA depending on the amplitude of the signal. Can someone help me explain the reason for this occurring. It makes sense to me that the op amps are 'working' harder due to larger voltage swings of the signal, but this explanation seems insufficient for my colleague. They don't really teach effects on power consumption at this low of levels in school.

thanks

kyle

  • Kyle,

    Can you provide a circuit diagram?

    Regards, Bruce.

  • Sorry Bruce I can't due to company policy. I was just looking for a theoretical explanation. I understand that is harder without a circuit to analyze for mistakes. Like said before, I would expect this behavior when at rest the board is only operating on a little noise very close to 0V and when signal is injected you then have voltage swings present on the op amps that range +/- 1-3.3V. I was just looking for a more theoretical explanation to please another individual. The smallest resistor in any feedback or input stage to the op amp is 1M, so i dont think we are burning excess power to ground anywhere.

    thanks

  • Kyle,

    The most common reasons for unexpected current increase include:

    • Signal dependent current in feedback resistors (includes internally in the INA).
    • Current increase occurs in some op amps in instrumentation amps when their outputs hit the supply rails.

    If you would like to take this off-line in an email, we can keep it more private.

    Regards, Bruce