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TINA-TI: Iso-Forward circuit with LM5021

Guru 10825 points
Part Number: TINA-TI
Other Parts Discussed in Thread: LM5021

Hello E2E,

I want to do simulation an Iso-Forward circuit with LM5021 using TINA-TI, so I made a simulation file.
However, I couldn't to run it.
Please let me know miss point on sim-file.



  • Hello ACGUY,

    What type of analysis were you trying to run? The transient simulation with zero initial values ran when I tried on my machine with the default timing settings.



  • Hi Andrew,

    I copied the LM5021 spice model from snvm453. This spice model has normal operation on snvm453. However, it can't run on pasted file.
    I don't know cause not to run normally. Could you point out miss on schematic?



  • Hi ACGUY,

    Thanks for explaining your method of creating the schematic. I don't think a miss on your schematic is causing the analysis not to run normally. It's still running on my machine. Let's confirm we have the exact same analysis parameters and/or settings.

    1. Can you confirm you've performed all the relevant steps from the test bench description in snvm453? 
    2. Also, can you elaborate what you're referring to when you say:
    couldn't to run it.
    not to run normally
    • What exactly is happening? Are you getting an error message (like for a convergence issues)?
    • Do you have any warnings from the electronic rule check (ERC) that executes before the analysis?
    • What steps are you taking in trying to perform the analysis?

    Addressing these questions will help us solve this problem one step at a time.



  • Hi Andrew,

    I'm FAE from Japan distributor.
    I want to do design an isolated DC/DC circuit using TINA-TI with spice model of TI's device for expand sales.

    The LM5021 midel has operate on downloaded file, it can't switching operation with file I made.

    The LM5021makes a self biass power from VIN using built-in linear regurator. The self biass power is output to VCC-port.
    On the file I made, it does not rised up the VCC voltage. Therefor, this spice model has not switching operation.

    I think the cause for not switching operation is there on the file I made.

    If you could point out some miss point from the file, it to be help on me.

    Best regards,

  • Hi ACGUY,

    Thanks for explaining your role, region, goal, and describing your issue. 

    I'll take a closer look at the file you created and suggest some edits. 

    Please give me 48 hours to review the full schematic including transformer specifications.



  • Hello,

    Upon further inspection, R7 isn't the root cause.  There's a number of changes I'd recommend you make, please see the modified file, attached.

    Most of the changes can be accounted for by the CS and COMP circuitry, in addition to VCC capacitor size.

    You may consider using a bootstrap winding off the transformer to feed the VIN with a regulated voltage. See the attached image to see how the as VIN starts to drop, VCC out starts to droop, this is showing running in burst mode. Dedicated VCC bias winding can solve this. 

    Also, you may consider trying to run this simulation in PSPICE for TI if you have further issues.