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OPA928: Natural Slewrate ?

Gabriel Berthet
Prodigy 10 points

Part Number: OPA928
Other Parts Discussed in Thread: TLV9001, OPA197

Hi TI Team, 

Following the lecture of your application note : Ramping Up on SlewRate
I discovered that for my application and for the OPA928, the natural slewrate of the amplifier is critical because of the increase of the voltage difference between the inputs, VID to produce the SlewRate. 
Therefore i have some questions on the OPA928 : 

it seems like there is a Slew Boost circuit on this amplifier can you confirm it ? 
If Yes what is the natural SlewRate before the boosting ? 

And Finally if you have some graph on the VID increase in comparison to the SR/SRmax i would gladly take it ! 
image.png

(A graph like this TLV9001)


Thanks you for your assistance ! 

  • +1
    TI__Mastermind 29765 points

    Post Edit:

    Hi Gabriel, 

    Please see Mike's comment. We were mistaken and the OPA928 does not have the same gain stages as the OPA19x family. We will collect this curve and post it within this thread. The app note is still useful for the slew boost discussion, but we will have a better idea on the behavior of the OPA928 soon. 

    Hi Gabriel, 

    The OPA928 has slew boost circuitry. The slew boost circuitry in this device is activated prior to the amplifier reaching its flat natural slew rate limit. The OPA928 has a similar internal gain stage as the OPA19X family. I released an app note on Full Power Bandwidth and Op Amp Distortion that can be found here that includes details regarding the OPA197:

    https://www.ti.com/lit/an/sdaa309/sdaa309.pdf?ts=1779307965353&ref_url=https%253A%252F%252Fwww.google.com%252F

     Please refer to the Output Rate of Change (V/us) vs Input Differential Voltage (V) plot. Right around 0.1V differential is approximately when the slew boost activates. The THD increases due to this non-linearity however the part shouldn't triangulate the waveform at this level. 

    Note that the OPA928 is not exactly the same as the OPA197.  We will need to measure the OPA928 Slew rate vs. VID curve, we will need approximately 1 week to get this information to you, and will post when it is available.

    Best Regards, 
    Chris Featherstone

  • 0 in reply to Chris Featherstone
    TI__Genius 15045 points

    Hi Gabriel,

    We've had to edit the post above, I had misinformed Chris about the relative accuracy of the OPA197 vs. OPA928 VID vs. Output slew curve.  We will get the curve measured for OPA928 and post here, give us a week to get this back to you.

    Regards,
    Mike

  • 0 in reply to Michael Hartshorne
    Prodigy 10 points

    Hi, Thanks you for the clarification, i will be waiting for the correct curves. 

    Thanks! 
    Gabriel

  • 0 in reply to Gabriel Berthet
    TI__Mastermind 29765 points

    Hi Gabriel, 

    Thank you for you patience. We have the parts and will be making the measurement shortly. I will respond here with the results once they are available. 

    Best Regards, 
    Chris Featherstone

  • 0 in reply to Gabriel Berthet
    TI__Mastermind 29765 points

    Hi Gabriel, 

    We have measured the Output Rate of Change vs Input Differential voltage. Note that the slew boosted circuit is activated prior to the onset of the natural slew limit. I hope this information is helpful. Let us know if you have any questions.

    Best Regards, 

    Chris Featherstone