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OPA462: while the device is disabled

Noriyuki Takahashi
Genius 10160 points
Part Number: OPA462

Hi team,

According to the datasheet, it seems that the output impedance just increases to about 160kOhm while the device is disabled.

But are there any changes else while the device is disabled?

Regards,

Noriyuki Takahashi

  • 0
    TI__Genius 10160 points

    Hi team,

    One more question.

    Could you also tell what the output voltage can be while the device is disabled in case of adder circuit or Non-inverting amplifier circuit?

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Mastermind 21067 points

    Noriyuki,

    When the amplifier is disabled the output stage is turned off.  The output will float to a small voltage.  If the output is connected to a load it will be pulled to the load voltage.  The non-inverting input will remain as it was before disabling the output.  I tested the functionality with the EVM using a adder circuit.  Let me know if you have some specific additional questions.  The EVM is useful for this kind of test.  You may consider getting a copy.  See attached PDF:  opa462evm suming circuit.pdf

    Best regards,

    Art

  • 0 in reply to Art Kay
    TI__Genius 10160 points

    Art, 

    Do you mean that the ouput voltage can be below in both non-inverting and a adder circuit?

    1. When the amplifier is disabled, the output will float to a small voltage.

    2.  If the output is connected to a load it will be pulled to the load voltage.

    Art Kay said:
    If the output is connected to a load it will be pulled to the load voltage. 

    What do you mean the load voltage?

    Do they need to take care of the loop stability in case of disabled, too to prevent the oscillation?

    Regards,

    Noriyuki Takahashi

  • +1 in reply to Noriyuki Takahashi
    TI__Mastermind 21067 points

    Noriyuki,

    I hope the additional detail below helps.

    1. Question: Do you mean that the output voltage can be below in both non-inverting and a adder circuit?  Answer:  In my setup I used +/-12V supplies.  I used two 1k resistors for the summing circuit.  Those resistors were connected to positive voltages (3V and 5V).  The voltage on the non-inverting input was the expected 4V (i.e. 1/2 ( 3 +5) = 4).  The output transistor are off, but some signal from the input will feed through to output.  I measured the disabled output with multiple different input conditions.  See attached.  It is possible for the output to go slightly negative with positive inputs applied.
    2. Question: What do you mean the load voltage?  Answer:  I mean the voltage the load is connected to.  Typically the load is connected to ground, but this is not always the case.  If your load is connected to ground, the load will pull the output towards ground.  The document below shows how different load values impact the output voltage when the amplifier is disabled. 
    3. Question:  Do they need to take care of the loop stability in case of disabled, too to prevent the oscillation?   Answer:  No. When the amplifier is disabled they do not need to take stability into account.  The device is no longer acting as an amplifier.  The inputs are high impedance and the output is no longer driving as a normal amplifier does.  Any output voltage is feedthrough from the internal stages.

    4300.opa462evm suming circuit2.pdf

    Best regards,

    Art