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TPS7H5005-SEP: Spice simulations show large output current oscillations

Steven Floyd
Prodigy 20 points
Part Number: TPS7H5005-SEP
Other Parts Discussed in Thread: PMP23193, TPS7H5001-SP,

Tool/software:

I would like to use the TPS7H5005 / 5001 in a push-pull application, similar to the reference design in the datasheet. Whenever I try to simulate the system, I see large oscillations on the output voltage as well as the current  through the output inductor as soon as the synchronous rectification kicks in. These oscillations also seem to defeat the current limiting effect of the CS_ILIM pin, as I see it exceeding 5 V routinely. Is this a limitation of the transient spice model, or am I missing something?

In an attempt to try to compare Spice model to reality, I copied the schematic in the reference design for the buck solution:  https://www.ti.com/tool/PMP23193 . I saw output oscillations on the order of 2.2 V, not the +/- 50 mV described in the test report on PMP23193. So I am really wondering if there are any additional steps I should be taking in simulation to get a more accurate representation of reality?

Thank you for any information you can provide.

-Steven

  • 0
    TI__Mastermind 26055 points

    Hey Steve,

    There are often presets we add to our schematics that are required to run the models properly.
    Things such as time step can change things drastically.

    Do you see these issues when you run the schematics we provided?
    https://www.ti.com/product/TPS7H5001-SP

    (They are the same model, feel free to try out the schematics)

    Thanks,
    Daniel

  • 0
    Prodigy 20 points

    Daniel,

    I am currently using LTSpice, not PSpice, and cannot run the schematics in full. I import individual models into LTspice and then run the simulations. Do these models work in LTSpice, or are there issues with changing programs?

    Thanks for the information.

    -Steven

  • 0 in reply to Steven Floyd
    TI__Mastermind 26055 points

    Hey Steven,

    There was an update awhile back that fixed some issues that were specific to how LTSPICE interpreted the model.
    Could you try using the TPS7H5001-SP PSPICE model in LTSPICE for your schematic instead?
    Its possible the update didnt happen to the TPS7H5005-SEP model.

    There may also be some set-up issues with LTSPICE we are unaware of.
    Because of the needed accuracy of the internal signals, things like step-size can be very important.

    Thanks,
    Daniel

  • 0
    Prodigy 20 points

    Daniel,

    I downloaded the TPS7H5001-SP Spice model and am now seeing convergence in my models. Thank you for that.

    As a semi-related question, when looking at the datasheet's typical application schematic, Figure 9-1, I notice that the windings on the transformer secondary side are reversed from what one would expect in a push-pull application. To wit; when looking at LP2 and LS2, have FETs driven by OUTA and SRA respectively, one would expect the dot on LS2 to be pointing towards the FET so that it is energized when LP2 is off. Is this reversal intentional, or a typo?

    Thanks again for the help with the correct download.

    -Steven

  • 0 in reply to Steven Floyd
    TI__Mastermind 26055 points

    Hey Steven,

    Good to hear.

    I believe you have found a typo in the datasheet.

    Thanks,
    Daniel