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OPA991: SPICE model for shutdown function

Timothy Cheehan
Prodigy 10 points
Part Number: OPA991
Other Parts Discussed in Thread: OPA2991, OPA341

TI-TINA SPICE Model for OPA991 uses the dual Opamp OPA2991 model. However, the OPA991 has a shutdown pin function that is not present in the OPA2991. How does one simulate the shutdown function of the OPA991?

  • 0
    TI__Mastermind 24080 points

    Hi Timothy,

    Welcome to the E2E forum! 

    Properly modeling an op amp in shutdown is complicated because it behaves very differently than what it would normally do. I don't have any easy answer to how to run a simulation on the op amp, but you can take a see how the op amp behaves in shutdown by looking at the electrical characteristics table in the datasheet. I highlighted some of the key 

    Is there anything in particular you are wanting to see when the device is in shutdown? 

    Best Regards, 

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    Prodigy 10 points

    Thank you Robert.

      I am using the shutdown to interrupt the feedback loop controlling the irradiance output of an LED and was trying to simulate the loop startup conditions when coming out of shutdown. I started with an OPA341 that has the shutdown pin modeled in TINA but the model was not working well and produced unachievable output voltages of three times V+ when the loop was turned on. Some experimenting showed that having a pulldown resistor (10k) to V- on the opamp output was an issue for the model. If the output was pulled down to a higher reference voltage (>30mV above V-), things improved. It looks like I will need to build and test the shutdown function.

      I also can force the LED output off with the DAC controlling the setpoint but do want the additional complete disconnect feature of the shutdown function to quickly and completely shut off the LED.

    Regards,

    Tim

  • 0 in reply to Timothy Cheehan
    TI__Mastermind 24080 points

    Hi Tim,

    Unfortunately we don't have the best shutdown models. I can talk with the modeling team about the OPA341 to see why it's behaving strangely. 

    We do have some content to help you better understand what is happening with the op amp. It's not for the OPA991 but it can still be helpful. Designing for TLV90xxS Operational Amplifiers With Shutdown is the name of the document. It should give you a better idea of how the op amp will behave when it's transitioning from on to shutdown. 

    I hope this helps.

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    Prodigy 10 points

    Robert - The document was helpful and confirmed the shutdown function as implemented in the design should be fine.

    Thank you,

    - Tim

  • 0 in reply to Timothy Cheehan
    TI__Mastermind 24080 points

    Hi Tim, 

    Glad to hear that the content helped! 

    Is there anything else you need? 

    Best Regards, 

    Robert Clifton