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THS3491: Transresistance gain drift

Eric Wells
Prodigy 155 points
Part Number: THS3491
I am concerned with transresistance gain drift and was curious if more information could be provided. A temp coefficient would be useful, along with any other sources of expected drift data over time. The datasheet specified 5M ohm min to 8 M ohm typ, I was wondering what testing was done to verify this as well.
  • 0
    Guru 140200 points

    Hi Eric,

    I know that doesn't answer your question, but the usual approach would be to choose an amplifier that provides so much headroom that these drifts wouldn't play a role.

    Maybe figure 6 of datasheet is helpful?

    Kai

  • 0
    Guru 47535 points

    Well Eric, 

    The open loop transresistance  gets into the closed loop gain as a LG/(LG+1) term where the LG is approx. that transresistance divided by the feedback R. Very small part of the overall gain drift. 

    That said,the datasheet min is a worst case designer simulation using full process variation models. There is however a limited number of devices run through full ATE overtemp at release - this would include everything shown as an "A" spec in the far right column - including transresistance - that data exists somewhere, perhaps someone can pull it out.

  • 0 in reply to Michael Steffes
    Prodigy 155 points

    Hi Michael,

    Thanks for the response, I am definitely interested in seeing the data measured for transresistance to get the "A" specification rating. Can someone at TI provide this information to me?

    Thanks,

    Eric

  • 0 in reply to kai klaas69
    Prodigy 155 points

    Also, thanks for the comment Kai. Yes, I understand your point having an amplifier with much larger transresistance or open loop gain where it is not a design limiting factor is normally the approach taken. Unfortunately figure 6 does not provide enough information for me, I was hoping to see an actual dataset or get a number for gain drift per C.

  • 0 in reply to Eric Wells
    TI__Mastermind 22360 points

    Hello Eric,

      Unfortunately, we do not have data for specifically gain drift per C, but I can share additional frequency response varying with temperature data offline. I also have some data on release (as Michael mentioned) for open-loop transimpedance gain numbers at various temperatures that I can share as well offline.

    Thank you,
    Sima 

  • 0 in reply to SimaJalaleddine
    Prodigy 155 points

    Thanks Sima, yes please share the information with me. I notice on the datasheet it specifies the test conditions are RL = 500 ohms and Vo = +/-10V, if you have any data when RL is changed or Vo is outside of the +/-10V range please let me know as well - Would you expect the transimpedance gain to change much as Vo gets closer to the supply rail?

  • 0 in reply to Eric Wells
    TI__Mastermind 22360 points

    Hello Eric,

      Sorry for the late response, I do not have any additional data other than what is presented in the datasheet for variations in output voltage swing and load resistance. It does change a bit in the frequency response, check Figures 4, 5 (impedance load), and some of the pulse response vs output voltage figures. 

    Thank you,

    Sima