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OPA2277: Guarantees no phase reversal when used in unity gain

Conor
Guru 10050 points
Part Number: OPA2277
Other Parts Discussed in Thread: OPA277

Hi,

The description section on the first page of the OPA2277 data sheet has the following description.
------------------------------------
OPA277 operational amplifiers are easy to use and free from phase inversion and the overload problems found in some other operational amplifiers.
They are stable in unity gain and provide excellent dynamic behavior over a wide range of load conditions.
------------------------------------

I understand that this statement guarantees no phase reversal when used in unity gain (voltage follower), is that correct?
Or does it guarantee that the op amp output phase inversion and saturation will not occur when an input voltage exceeding the common mode input voltage range is applied?

Thanks,

Eevee

  • 0
    TI__Genius 10085 points

    Hi Eevee,

    These are two separate, independent statements from the datasheet. The OPA277 is free from phase inversion regardless of the gain setting.

    The datasheet indicates that phase reversal will not occur when an input voltage exceeding the common-mode input voltage range is applied. Saturation of the input transistors will occur when the input common-mode range is violated which will put the device in a non-linear state of operation as is the case for any op amp. To maintain linear performance, it is important to not violate the input common-mode range, even for devices that do not exhibit phase reversal.

    In the simulation below, the input common-mode is violated and the input transistors are saturated resulting in a non-linear or "clipped" output signal. Notice the phase is not inverted.

    For large magnitude input violations, it is possible for a partial phase reversal to occur that presents as an additional distortion on the clipped output signal. In the simulation below, the input common-mode is violated by 1V and a partial phase reversal can be seen presenting as a slight dip on the clipped portion of the output signal. This output is far preferable to the total phase inversion in which the output slams into the opposite rail, as shown in the next figure.

     

    The figure below shows the response of an op amp that is not protected from phase reversal.

    Regards,

    Zach