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TPS7H1101A-SP: TPS7H1101A-SP Transient model vs WCA model, Checking stability

Mohammad Rajabi1
Prodigy 130 points
Part Number: TPS7H1101A-SP
Other Parts Discussed in Thread: TPS7H1101-SP, TPS7A4501-SP

Sup y'all,

Here it's me again, your boy Mamad, evaluating the TPS7H1101A-SP models shown below in this thread by using OrCAD PSPice.

I wanted to evaluate the stability by the well-known methods, inserting a capacitor and indicator. After that check the  Bode diagram and Nyquist diagram.

My expectation is that they should give me relatively similar results like the results from the DC simulation.

Bode diagram for Phase and Gain, and the frequency response in real and imaginary formats:

Results based on the TRAN model Results based on the WCA model

As you can see the results are very different.

I also show the schematics:

The schematic using the WCA model to evaluate the open-loop gain frequency response:

The schematic using the TRAN model to evaluate the open-loop gain frequency response:

However, the simulated DC operating points are almost the same.

I just wonder why there is a difference? Is it because of TPS7H1101A-SP vs TPS7H1101-SP? I assume the WCA model is the correct one for TPS7H1101A-SP LDO?

I have to know the start up- conditions as well, can I trust the transient simulation based on the TRAN model if I want to use TPS7H1101A-SP LDO?

  • 0
    TI__Guru 62930 points

    Mamad,

    Let me research the history of these models and get back to you shortly.

    Regards,

    Wade

  • 0 in reply to Mohammad Rajabi1
    TI__Guru 62930 points

    Mamad,

    I think the answer is similar to your query on the tps7a4501-sp.

    The earlier model was intended to only be transient and no efforts were put in to tune the model for AC response.

    In general there are transient models and avg or AC models for most of the power products.   The linear LDO models are capable of being "all in one", but that may not have been fully comprehended in the earlier models.

    I am still waiting for some confirmation from some engineers that were involved at the time.    I will reply back to this post with confirmation.

    I can confirm that the WCA model was tuned for AC analysis after aging and TID.

    Regards,

    Wade

  • 0 in reply to Wade Vonbergen
    Prodigy 130 points

    Hello Wade,

    Let me know if my plan works or not.

    I have to do a worst-case analysis on the LDO considering the tolerance of the device itself and the surrounding components.

    I can apply this analysis on many parameters such as Vout, stability.

    As far as I understood, I can use the WCA model for TPS7H1101A-SP and do the Monte Carlo analysis to evaluate the variation of V_out considering the surrounding components. Can I also consider the tolerance of the IC somehow?

    If I apply the Monte Carlo analysis to evaluate the phase/ gain margin, then I am evaluating the phase/ gain margin after aging and TID? If the difference after and before aging is relatively considerable then probably somehow I should evaluate the stability before aging as well, correct?

  • 0 in reply to Mohammad Rajabi1
    TI__Guru 62930 points

    Mamad,

    I need to check with some of the team that created this model.

    I do know that that the AC response was tuned for TID and aging.   The base model is created from full design spice sims, so the process should be included to a degree.

    However, I am uncertain on if TID and aging effects are applied to the DC specs.  They are applied to the AC response.

    There is TID and aging data that I can provide can be used to help analyze the DC response.

    So, you can verify your stability with the WCA model, and use radiation data and life test data to verify Vout variation.

    I will send you an email off the forum to discuss the data available from TID and life test and what information I get from the team.

    Regards,

    Wade

  • 0 in reply to Wade Vonbergen
    TI__Guru 62930 points

    Mamad,

    Lets handle the remainder of this via email.  You should have seen an email from me.

    I will mark this post resolved.  We can re-open it if necessary.

    Please click "This Resolved My Issue" to close out this post.


    Regards,
    Wade