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OPA835 output impedance

Vinson Go
Prodigy 60 points

Other Parts Discussed in Thread: OPA835

For the OPA835, the data sheet shows that the output impedance goes high when the op amp goes into power down mode.  If the power is disconnected, does the output impedance also goes high?

  • 0
    TI__Genius 13335 points

    Hello Vinson, 

    Yes, but it depends. Basically, you can think of the output stage as a PNP/NPN pair connected to the supplies (shown below).

     

    In the power down case, the bases are shorted to the supplies so you get Vbe=0 and no current flow from emitter to collector. In reality, there are also ESD diodes protecting the output so if the applied voltage is too high/low the ESD diodes get triggered and substantial current can flow in/out the output pins.

    In the case where power is disconnected it matters whether the rails are shorted to ground or floating. If grounded again, the transistors will be off and no current will flow.

    If they are floating, then there is the possibility that they can turn on, but I don't know why you would want to do this.

    Hope this helps.

    Regards,
    Luke Lapointe
    High Speed Amplfiiers