Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

  • State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 48 subscribers
  • Views 223 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THS3491: THS3491 Slew rate

Mahsa barkabian
Prodigy 50 points
Part Number: THS3491
Other Parts Discussed in Thread: THS3061,

slew rate of THS3491 is 8000 V/us ((20% – 80%) and slew rate of THS3061 is 7000 V/us for 20V-step and 5700 V/us for 10V-step (25% to 75% level) which indicates that THS3491's rise time shall be lower than the latter opAmp, which surprisingly is not and THS3491 has 1.3ns rise time and THS3061 has 1ns rise time.
Could you please elaborate on why despite the rule of ''higher slew rate results in lower rise time'', the rise time of THS3491 is more than THS3061? and why there are various conditions in reporting slew rate and what do they stand for?

 

  • 0
    Guru 48395 points

    There is some confusion in those older datasheets vs more recent like the THS3491. It is very unlikely that the THS3061 is physically faster edge rate than the THS3491. For example, do you see any 10V step responses in the THS3061. No, there are not actual plots as they probably could not in that time frame make the measurements. The 1nsec typ is probably a designer sim. In the THS3491, an input edge rate of 1nsec is noted, so the 1.3nsec number is an RMS of the input and device rise times. 

    The old THS3061 was being done by folks kind of new to high speed amps, this front page plot has always been an egregious error in that the slew rate does not change with step size, this is just a constant linear rise time dividing into a larger step size, pretty confusing to new designers I would expect, 

    If you had interest in a more thorough discussion of these issues, consult this article, 

    https://www.edn.com/what-is-op-amp-slew-rate-in-a-slew-enhanced-world-part-1/

  • 0 in reply to Michael Steffes
    Prodigy 50 points

    Thank you so much for your reply.
    So you mean surely THS3491 is faster than THS3061 and has a lower rise time?
    How can we prove this? via which parameter?

  • 0 in reply to Mahsa barkabian
    TI__Expert 6050 points

    Hi Mahsa,

    As Michael pointed out, you can check the datasheet of the THS3491 and find rise time information in the Electrical Characteristics table or you can look at the pulse response figures in the typical characteristics section of the datasheet

    Also as Michael pointed out, there are no plots of pulse response for the THS3061 to compare to these measurements. If you would like to prove the parameters, we offer the THS3061EVM that can be used for testing purposes. 

    Thanks,

    Nick

  • 0 in reply to Nick Nauman
    Prodigy 50 points

    Dear Nick,
    Thank you so much for your reply. I will go for THS3491 and I hope everything goes well.

  • 0 in reply to Mahsa barkabian
    TI__Expert 6050 points

    Hi Mahsa,

    I will close this thread. If you have any further questions, please feel free to respond to this thread or start a new thread.

    Thanks,

    Nick