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OPA454: How close to negative rail can you get your output

Russell Wetherley1
Expert 4255 points
Part Number: OPA454

Hello E2E, I am planning to use OPA454 to simulate 0 to +40VDC, I am going to make the op amp to have gain of 4 and input 0-+10VDC.  I want to verify with you how low V- should be, because the datasheet doesn't say much about V-.  For the simplicity of my work, I want to just tie V- to ground, but I am also afraid that would not allow me to have 0V at the output of the op amp.  On page 6, it says that the output voltage can swing from V- to +1 or +2V.  With V- tied to GND, would I expect around 1V on the output at Vin = 0V? 

Thanks!

Russell

  • 0
    TI__Mastermind 22825 points

    Hi Russell,

    Yes, you'd only be able to get within 1V of V- with light load. If you use 40V single supply, your guaranteed minimum output voltage will be 1V with a light load. Your "typical" swing can be closer but that is not guaranteed for all devices you'll be getting. Figure 10 shows 1mA output can swing much closer than 1V towards V- of -50V- that's a typical performance plot and not guaranteed.

    Any possibility of using a negative bias voltage on the OPA454 V- pin?

    There are some switched cap sources that can do this (provided the current demand is not excessive). Here is a list of some of these products: 

    Regards,

    Hooman

  • 0 in reply to Hooman Hashemi
    TI__Expert 4255 points

    Thank you Hooman!

    One additional question:

    My customer is concerned about not using symmetrical power supplies.  Do the power supplies need to be symmetrical in order to ensure proper output voltage?  I would imagine not, and I have never run into that issue, but I wanted to double check with you.  They would be using -12 and 45V supplies, gain of 4.  And 0-10V signals.

    Thanks!

    Russell

  • 0 in reply to Russell Wetherley1
    TI__Mastermind 22825 points
    Hi Russell,
    The supply voltages do not need to be symmetrical.

    Regards,
    Hooman