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OPA1622: Noise in output during shutdown.

William Anderson1
Prodigy 10 points
Part Number: OPA1622

Looking for info, appnotes, etc. on output characteristics during shutdown. With head phone like loads (using the eval board) the output seems controlled and quiet. With higher load impedances (100k) the output during shutdown is noisy (white+?) and has audio input bleed thru. A 10k resistor to GND in parallel with the load helps significantly, but this seems like a poor solution to help quite "off time".  Any workarounds?

Thanks!

  • 0
    TI__Guru 60610 points

    Hi William,

    The input voltage noise in any op amp is an inverse function of Itail current biasing the input differential pair: Vnoise~1/Itail.  Therefore, it should come as no surprise that as the part gets shutdown, Itail goes down and thus voltage noise goes up until the output collapses on one of its rails.

    Engaging RC low-pass filter at the output during a shutdown should eliminate this problem.  If you need further help, we would need to see your actual schematic.