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TINA-TI: Iso-Forward circuit with TPS55340

Guru 11170 points
Part Number: TINA-TI
Other Parts Discussed in Thread: TPS55340,

Hello E2E,

I received a technical supporting request from our customer. Apparently, customers want to build Iso-Forward converter with devices that have built-in FET.
I tried to design Iso-Forward converter using the TPS55340 with TINA-TI.
However, it can't operate normally. That output voltage is drop soon.

Please pointout some miss points from posted file, and advice me.

Regards,
ACGUY

Forward-2.TSC

  • Hi ACGUY,

    Thank you for reaching out.
    I will have a look on the model and get back to you later today.
    Thank you very much for your patience.

    Best regards,
    Niklas

  • Hi ACGUY,

    I ran your simulation model and saw the same problem you described.
    After looking at the schematic, I noticed that the FB pin is connected to ground.
    This pin is necessary for the feedback loop and should be connected to the voltage divider at the output to set the desired output voltage.

    I would recommend to change the FB pin connection and check if the IC achieves a proper operation.

    For additional design support, I can also recommend the Flyback Design Calculation available on the product page.
    https://www.ti.com/product/TPS55340#design-tools-simulation
    It is a good tool for checking the optimal values for the schematic components and to see if everything is within spec.

    Please let me know if you need further help.

    Best regards,
    Niklas

  • Hello,

    Thank you for your cooperation.
    In the user's guide for EVM with flyback topology, the FB is connected to GND with 0-ohm.
    www.ti.com/.../slvu751a.pdf
    Does the schematic have misspoint for design?

    Regards,
    ACGUY

  • H ACGUY,

    Thanks for the feedback.
    No, you are right, the EVM users guide should not include any errors, means if you took the EVM schematic as reference, the design should be valid...
    I will loop in another team member, who has more experience with this device. If we cannot find the error in the schematic, the problem might actually lie in the TINA model itself.
    In this case, it might be faster to switch to the PSpice model an re-create the schematic there, until the TINA model error gets fixed. PSpice models are generally more up-to-date and run more precise.

    Either way, I will get back to you earlier next week, once I have some results.

    Best regards,
    Niklas

  • Hi ACGUY,

    Sorry to keep you waiting.

    After having some discussions and simulations, I do not suppose that there is an error in the TINA model. I worked with your simulation model and found out, that the voltage drop seems to be in some kind of relation with the soft-start feature and the Vss cap.

    I also found out, that a higher frequency might be sufficient to fix the problem. (E.g. reducing the resistor at the FREQ pin to 137kOhm like in the EVM model.)
    A reason for this could be, that the higher current ripple at lower frequency triggers the overcurrent protection, but this is just speculation.
    Therefore, I would recommend to create a simulation with faster switching frequency and less load to get a stable operation. From there, it should be easier to find additional improvements.

    In comparison to the EVM model, the TINA model does not include the external soft-start feature implemented with the two diodes and a capacitor, so it might be an improvement to the circuit to implement these as well.

    Please let me know, if you have further questions.

    Best regards,
    Niklas

  • Hi ACGUY,

    I hope the customer made progress with the converter design.
    As there are no further comments, I will close this thread for now.
    If you have additional questions, you can reply below to re-open the thread.
    Otherwise feel free to click on the resolved button.

    Thank you and best regards,
    Niklas