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OPA1632 Shutdown Question

John La Grou
Intellectual 340 points
Other Parts Discussed in Thread: OPA1632

I'm looking at the OPA1632 as a candidate for an audio application.

1.) Would the shutdown mode be considered an audio-quiet event (smooth ramp)? Or is there some associated signal glitch?

2.) When in shutdown mode, what do the outputs look like? Impedance? Current? Tri state?

Thanks,

JL

  • 0
    TI__Guru 69181 points

    JL,

    Since OPA1632 is implemented on bipolar process, its shutdown function just reduces the quiescent current so there should be a smooth transition between the active and disable modes. In the shutdown mode the quiescent current is reduced from typical of 14mA to approximately 850uA, therefore, the output stage is NOT in a high-impedance state. For that reason, the shutdown function cannot be used to create a multiplexed switching function for multiple amplifiers.

  • 0 in reply to Marek Lis
    Intellectual 340 points
    Thank you. Do you happen to know the actual measured output impedance when in shutdown mode?
  • 0 in reply to John La Grou
    TI__Guru 69181 points

    John,

    The output impedance is a function of the collector current as well as frequency - see below.  Since in bipolar transistor ro~1/Ic, decreasing the quiescent current from 14mA to 0.85mA, will result in approximately 16x increase in the low frequency open-loop output impedance.  But since the graph below shows a close-loop output impedance of 0.3 ohm at DC, which translates into an open-loop output impedance of around 3kohm (typical DC AOL=78dB), I would guesstimate in a shutdown mode its close-loop output impedance to increase to about 5 ohm while open-loop output impedance to be around 100 ohm.

    If you are truly concern about any audible noise created by OPA1632 shutdown function, the only way to know for sure is to test it in the specific application with specific headphones (speakers).

  • 0 in reply to Marek Lis
    Intellectual 340 points
    Excellent. Thanks so much!