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TINA/Spice/TLE2426: problems creating a Tina-TI representation which uses the TLE-2426 with a single supply op amp

Bob Edwards
Prodigy 210 points
Part Number: TLE2426

Tool/software: TINA-TI or Spice Models

Hi,

I have been working with Tina-Ti to create a design for an inverting opAmp circuit using an OPA350 or equivalent as a voltage follower whose input comes from a INA121, and which runs off a single 5V dc supply. The 350 input is an amplified 1V 10Hz sinusoid out of the 121, and incorporates a TLE2426 to provide a 2.5V reference at Vin+. I have started with a design that uses two identical 1Meg resistors in a conventional configuration to split the 5V OPA350 supply and it works like a charm (there is an output capacitor from the INA in front of the paired resistors). But when I try to introduce the TLE2426 as a replacement in the OPA350 portion of the circuit I get output which is a ripple superposed on 2.5V DC, indicating that my setup for the 2426 is really wrong. I have tried to follow designs I've seen on the internet to introduce the TLE.

I'm guessing that I am misunderstanding the difference between the chassis ground and the reference ground, but cannot see how. Can someone point me to a circuit layout that will work in the TI simulator?

Thanks

  • 0
    TI__Intellectual 820 points
    Hi Bob,

    Please upload and share your TINA .TSC file schematic here. We will look into this.
  • 0 in reply to Ahana Ghosh
    Prodigy 210 points

    Hi,

    I am enclosing one of the attempts I made at introducing the TLE2426 in place of two 1 Meg resistors which split the power supply rails to set the Vin+ of the 350. I'm sure this is wrong, but I could not figure out how to set the 2426 up for the op amp in a voltage follower mode. My 2426 is a three pin version. Not sure what the four pin version does differently.

    Am also including a zip of the Tina schematic file I'm using for the TLE (not sure if I uploaded correctly, as the representation looks weird in the post). The original post from yesterday uses two 1 Meg resistors to split the rail.

    Bob E.

    1NA 121 AC Inputv_A2.zip

  • 0 in reply to Bob Edwards
    TI__Intellectual 820 points

    Hi Bob,

    I believe you are using the 1uF cap for blocking the DC.

    As I have seen when using TLE2426, the output circuitry of TLE2426 and INA is having some unwanted interaction.

    So better to use isolation between these 2 and use a bigger blocking capacitor which will pass the AC signal more efficiently.

    I have made some changes and attached the schematic.

    Please see, this solves.

    1NA 121 AC Inputv_A2_solution.TSC

  • 0 in reply to Ahana Ghosh
    Prodigy 210 points

    Thanks for the response and the TLE! I must admit, I am confused by the terminology re VCVS1. I looked it up and am frankly clueless as to what it represents. Does it represent a circuit element or an entire circuit? What would it look like in an actual wired circuit? Any light you could shed on the symbol and what sort of active circuitry it represents would be much appreciated.

    Incidentally, the original TLE you sent stops at 15% with my copy of Tina-TI. Not sure why.

  • 0 in reply to Bob Edwards
    TI__Intellectual 820 points

    Hi,

    The VCVS is just a ideal buffer, providing isolation between these two and can't be realized in real circuit like that.

    I just placed it for testing in the model and show that the output  stages of the INA and TLE device is having some unwanted interaction(instead of simple superposition) as they are getting connected/shorted via the 1uF cap

    For isolation between the 2 blocks, L-C can also be used like this,

    Regarding running of the file, which TINA version are you using? Kindly use latest version  9.3.150.328 SF-TI

  • 0 in reply to Ahana Ghosh
    Prodigy 210 points
    I see now how you decoupled the two components, but I also noticed, I believe correctly, that it takes a very large choke to accomplish the task. I'm coming around to the viewpoint that the only way to ascertain whether the 2426 can do the job is to try it in an actual circuit.
    I want to thank you for all your help. It is much appreciated, and I'll close this out.
    The newest version to which I have access is 9.3.150.4.
    Again, many thanks!