How to find SPICE models?

Thread Starter

salvus

Joined Apr 2, 2020
34
Hi,

I recently came across the concept of SPICE simulations. For components I am interested in, I really struggle to find models to download though. I find TI component SPICE models quite easy to find, but I struggle with pretty much anything else. Say I find a component I like the sound of on something like LCSC, how do you find the SPICE model to see how it would affect the behavior of the circuit? I would have thought this would have been something that all manufacturers would just supply as default, however that doesn't seem to be the case.

Many thanks
 

Papabravo

Joined Feb 24, 2006
17,576
Manufacturer's have never shown much interest in using SPICE models as a marketing tool. I don't know if the companies that seem to have some interest in it would actually be candid about their reasons or experiences. I'm pretty sure they are not interested in having any significant number of people supporting software or answering questions about particular models. That function seems to be adequately handled by users groups.
 

Thread Starter

salvus

Joined Apr 2, 2020
34
Many thanks. Is it that most people just tend to try and make their own model from the information provided in the datasheet?
 

Papabravo

Joined Feb 24, 2006
17,576
Many thanks. Is it that most people just tend to try and make their own model from the information provided in the datasheet?
That approach is more difficult than it sounds, but there are people who attempt it. When manufacturer's make models they have volumes of semiconductor process data they can use to verify the "appropriateness" of the model. Notice that I did not say accuracy. You don't get accuracy when you purchase parts and you certainly won't get it from simulation. What also happens over time is that process improvements will outpace the updating of the models. Some models in current use are from the 1970's.

The trend seems to be that constructing behavioral models for complex parts rather than transistor models allows for more rapid simulations at the expense modeling actual device behavior. This is especially true with the encrypted or proprietary models. If you haven't discovered it already I recommend @Bordodynov 's archive at:

http://bordodynov.ltwiki.org/

You want the 17 Meg zip file listed first on his page.
 

Thread Starter

salvus

Joined Apr 2, 2020
34
Many thanks. Do you tend to stick to components that have a spice model available? How much does that influence your decision when selecting components?
 

Papabravo

Joined Feb 24, 2006
17,576
Many thanks. Do you tend to stick to components that have a spice model available? How much does that influence your decision when selecting components?
I've been retired for 8 years, so my experience is not recent. I used simulation a couple of times over the years that I did designs mostly for input and output interfaces for microcontroller based systems. I never relied on it for component qualification or analysis. The best example I have was a current limited high side switch for industrial automation systems, based on The MJD350. It was the first surface mount part that I used in a design and I was concerned about power dissipation.
 

eetech00

Joined Jun 8, 2013
2,808
Many thanks. Do you tend to stick to components that have a spice model available? How much does that influence your decision when selecting components?
I’ve used spice models quite a bit.
In my opinion, they are great for “proof of concept” and will provide some insight as to whether a design will work. But it is not a substitute for hardware prototyping. Even the best spice models cannot simulate the hardware with 100% accuracy.

Do you tend to stick to components that have a spice model available?
No

How much does that influence your decision when selecting components?
none
 

Thread Starter

salvus

Joined Apr 2, 2020
34
What would you do where there just doesn‘t seem to be a model available? Do you get any use from spice modelling in that case?
 

Papabravo

Joined Feb 24, 2006
17,576
What would you do where there just doesn‘t seem to be a model available? Do you get any use from spice modelling in that case?
Then I would either use a behavioral model or I would do as we did prior to 1973 when the first version of SPICE was released.
https://en.wikipedia.org/wiki/SPICE
We read the datasheet(s) carefully, talked to the FAEs, ordered some samples, and built our understanding of the parts. We actually got pretty proficient at it. Many successful products were designed and produced this way. Many still are.
 

eetech00

Joined Jun 8, 2013
2,808
What would you do where there just doesn‘t seem to be a model available?
Well...it depends on the complexity of the circuit and the cost and availabiilty of the parts. If its a simple circuit, and the parts are low cost and readily available, then it may be easier to build and test using real hardware. Of course, if you build with real hardware, then anything you need to know about the circuit can be obtained. Even information to help build models of the parts for use in future projects. Read on...

Do you get any use from spice modelling in that case?
That depends on what you expect to get out of a simulation. Ask yourself a couple a questions: Why am I simulating the circuit? And what do I expect to get out of the simulation?

Whether or not a simulation will meet the criteria you develop from answers to the questions above will determine how accurate the models will need to be should you decide to simulate.
 
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