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WEBENCH® Tools/tps568215: Load transient simulation diverge between Webench and TINA-TI

Elder Costa17
Expert 2825 points
Part Number: TPS568215
Other Parts Discussed in Thread: TINA-TI

Tool/software: WEBENCH® Design Tools

I have run the following project through Webbench:

Transient load response:

I exported the design to TINA-TI and modified it to mimic the simulation with some switches and current generator (see below).

I get the following result:

Ultimately I want to see the power supply behavior with a high decoupling capacitance of an FPGA design, that is the reason why I am doing this test (sanity check).

What am I missing?

Here iswebench_design_1450079_109.tsc the TINA file (I hope the attachment works).

  • 0
    Expert 2825 points
    OOPS, my question is about the amplitude differences shown on both graphs, around 1% transient on Webench, up to 5% on TINA.
  • 0 in reply to Elder Costa17
    TI__Expert 6425 points

    Hello Elder,

    1, I think The simulation tool couldn’t display Vin ripple and Vin behaviors. If you want to know Vin behavior, you can use EVM to run the load transient.

    If you don’t have EVM board, I can help you test.

    2, you said there’s some variation about amplitude between TINA and webench, i’ll double check then answer you.

    Edwin Zang

  • 0 in reply to Edwin Zang
    Expert 2825 points
    1- For now I am not concerned with Vin. Let's focus on Vout.
    2- You just have to compare the two graphs of Vout I provided. Webench shows less than 1% variation of Vout whereas TINA shows up to 5%. I hope the information I provided, including TINA-TI simulation file is sufficient for you or any one from TI with the required qualification to replicate my results and try to figure out what is happening.
  • 0 in reply to Elder Costa17
    TI__Expert 6425 points
    Hello Elder,
    This morning I didn’t have computer at my hand. I’m sorry to couldn’t help you check directly.
    I just now open the TINA file you provide, and find the rise time and fall time of output current is very fast when IC happens load transient . It’s just 1fs. You can check the component IG. On Webench, the rise/fall time of output current is 30us.
  • 0 in reply to Edwin Zang
    Expert 2825 points

    Hi Edwin, that makes sense. The rise/fall time totally passed unnoticed to me. I will change it and simulate again. Thank you very much.

    Best Regards.

  • 0
    TI__Expert 5745 points

    check the rising/falling edge of the load to make sure they are both same

  • 0 in reply to Edwin Zang
    Expert 2825 points
    Edwin, I just simulated after adjusting the rise/fall times. Now the match is nearly perfect. There is a tiny offset on the output voltages but that is probably simulator specific or some minor setting. Anyway that solves my issue. Thank you.
  • 0 in reply to Elder Costa17
    Expert 2825 points
    Edwin o Vental, I have two follow-up questions. They are more Webench/TINA-TI related but I hope you can help me with them or direct me to whom could help:

    1- I would like to add capacitance in parallel with the output capacitance Webench proposes, to simulate the impact of my circuit's decoupling capacitances (around 600uF with around 2mOhms resistance for this 1V supply). I could not find a practical way to do it in Webench. I tried to edit the schematics but I found the editor too limited. Maybe I did not look at the right place or did not look deep enough but I did not find a way.
    2- Assuming I need to use TINA-TI for some simulation like I did, I had to jurry-rig that circuit with the current generator IG1 and switches to switch from pure resistive load during startup to the IG to simulate the transient load. Is there a more straightforward way to do it?

    Thank you.

    Elder.
  • 0 in reply to Elder Costa17
    TI__Expert 6425 points

    Hello Elder,

    1, I write a document about how to add components on Webench. you can refer it.

    2, you can use current generator IG1 to run load transient directly. you can set IG1 time and waveform that you want.  it need't use switches.

    How to add component on Webench.pdf

    Edwin Zang.

  • 0 in reply to Edwin Zang
    Expert 2825 points
    Hello, Edwin,

    Thank you for the document, it was helpful. It saved me a couple of hours of trial and error work. It seems the Webench simulation is limited to startup though. So I have to use TINA-TI anyway to check transient response.

    Regarding IG1, I tried to use it directly but the controller did not start up, probably because I set IG1 current to 4A. It is not a big deal though.
  • 0 in reply to Elder Costa17
    TI__Expert 6425 points

    Hello Elder,

    Yes, the edit schematic option is enabled for starup simulation. if you want to run other type simulations, you can double click the component on schematic. you can follow below docment.

    In TINA, during soft start time, please set 0 output current. you can set like below.

    0456.How to add component on Webench.pdf