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AD-supplied model oscillates when more realistic components used

Thread Summary

The user encountered parasitic oscillations when substituting more realistic component models in the LT8376 Buck LED Driver example circuit SPICE model. The final answer suggests submitting a Technical Support ticket to Analog Devices for further assistance. The original model uses ideal components, and the evaluation board ( EVAL-LT8376-AZ ) does not exhibit the oscillation issue.
AI Generated Content
Category: Software
Software Version: 24.1.10 (x64)

From here:  https://www.analog.com/en/products/LT8376.html#tools-header

I downloaded this model: https://www.analog.com/media/en/simulation-models/spice-models/lt8376-buck-led-driver-example-circuit.asc

which is a model of this evaluation board:  https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards-kits/eval-lt8376-az.html#eb-overview

The model, as downloaded, does run but it makes use of only ideal supporting components.  When I try substituting better models (with the same values) for the components, like the 47uH output inductor, or the 0.47uF input capacitor (found on the board but not standard in the model), the model becomes rather unusable because of all the parasitic oscillations that result. This makes it rather difficult to explore possible acceptable alternate components because the model can no longer be trusted.  I have it on good authority that the evaluation board, and its real components, does not have this oscillation problem.  Is there anything that can be done to salvage the model so that it is usable?

  • Hi  ,

    Please enter this problem as a Technical Support ticket here:

    www.analog.com/.../support.html

    mike

  • on Aug 3, 2026 1:14 PM in reply to MStokowski Contains AI Generated Content
    +1

    As suggested above, I submitted a technical support ticket and the AD support staff person who responded confirmed that he too saw similar behavior (oscillation) when real-word components (rather than ideal components) were used in an LTspice simulation of this circuit.  He had no further suggestions other than "the circuit should work" and "perhaps this is more than LTspice could handle."  A further query from me to the LTspice support team revealed nothing new.  Later, as the board layout phase was wrapping up, I noticed a comment in the datasheet that suggested that the "Cc" compensation capacitor to ground on the "Vc" pin of the LT8376 may need to have a series resistor, "Rc",  included (which my circuit did not include) if "Cout" was greater than 10uF (my Cout was 20uF).  The datasheet's suggestion for picking the values for Cc & Rc was to see the "Typical Applications" at the end of the datasheet. But those typical applications were all over the map when it came to these compensation component values and no clear pattern for their selection could be found. 

    I submitted another request for support in selecting an appropriate Rc value to the AD hardware support team, explaining the problem, but so far it has gone unanswered. 

    I figured, "what the heck" and explained the problem to Google's Gemini AI and it turned out to be most helpful.

    In a nutshell, it suggested Cc = 0.01uF (I had had 0.001uF) and Rc = 56k.  When asked to defend this change, it offered the following:

     

    When these Cc and Rc values were plugged into my "real-world components" simulation, the simulated circuit worked quite nicely and did not oscillate at all.

  • Hi  ,

    Glad you figured it out.

    He had no further suggestions other than "the circuit should work" and "perhaps this is more than LTspice could handle." 

    Yeah, no. Not much falls into that bin. :-)

    mike

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