LM 2936 3.3

[Vern Moline]

am trying to simulate a circuit with Multisim and need a model for an LM 2936 3.3. called Ti etc w/o any result.
any help appreciated..

 

[bountyhunter]

That part is about 25 years old. We were not creating SPICE models for parts back then. Nat Semi eventually started making SPICE models on new parts but not for old parts. We had to pay contractors to develop the models and they didn't want to spend the $$$ on old parts already in the market.

The models were typically pretty useless anyway but nobody seemed to notice or care.

 

[ronsimpson]

The models were typically pretty useless anyway but nobody seemed to notice or care.

LOL
There are too many people making spice models that have never applied power to the part.
Many data sheets don't really reveal how the part works.
You need to know how to read a data sheet.
Even the models from the maker often are not quite right.

 

[bountyhunter]

LOL
There are too many people making spice models that have never applied power to the part.
Many data sheets don't really reveal how the part works.
You need to know how to read a data sheet.
Even the models from the maker often are not quite right.

"Not quite right?"

Some of the models were useless. The company doing the models were just programmers who didn't know what an oscilloscope was. We supplied them data and they made a model that spit out the numbers.

The last one I worked on was the LM2731. I had to take all the bench data they used to make the model. Then they claimed the model was "finished" and I start checking it and find out it doesn't agree with my data.

They claim my data must be wrong, because the model was right.

I say, then show me your data and let's figure out the difference.

They claim they have no data because their contract did not pay them to TEST the part, only develop a model.. If we want them to TEST, we have to pay them more money.

And National actually DID pay them more, to do what they needed to do to verify their model.

Bottom line, I eventually gave up and we threw out most of the model and developed a "guideline" for where the model data was accurate and where it was completely useless so I could advise customers what to use. I suspect most of the models are only accurate over a very narrow range of conditions but it's not my problem anymore.

But people still worship at the altar of the simulation and dinosaurs like me with bench data just let them.

 

[bountyhunter]

Just as an illustration about the accuracy of sim models... above I said that I worked with the guys who did the LM2731 model (at nat Semi). Well, TI bought Nat Semi. Just for laughs I went and looked up the LM2731 data sheet and look what TI added in bold letters:

"NOTE: Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality"

If that doesn't tell you what's going on, I don't know what would.


https://www.ti.com/lit/ds/symlink/lm2731.pdf

 

[ronsimpson]

I started with PWMs before I could get them. (make your own with op-amp and voltage compare and FF)
So I almost understand how they work.
I also know that most people don't reinvent the wheel. For the parts I designed I used "parts" that are in production. If I need a 1mhz op amp then just pick one in the book and connect it up. (in side silicon) Pretty much any piece of silicon in production is available to the IC designer to copy as one of his building blocks.

So when designing spice parts; I look at the response and gain of the different stages and find op-amps and such that are similar. (reverse engineering)

 

[eTech]

am trying to simulate a circuit with Multisim and need a model for an LM 2936 3.3. called Ti etc w/o any result.
any help appreciated..

TI has one but it is encrypted so will only work with TINA.

 

[Mikebits]

TI has a pSpice model for that part. According to NI, you should be able to use the model in multisim. You can get the spice model from the following link:
https://www.ti.com/lit/zip/snvm347

You will also have to create a custom part in multim for your part. It is not hard to do. If you don't know how to create a custom part then follow this link for creating a custom part in Multisim.
Creating custom parts in Multisim

That should do it, let me know if you need further help, I have been creating custom parts in Mutlsim for awhile.

 

[MikeMl]

TI has a pSpice model for that part. According to NI, you should be able to use the model in multisim. You can get the spice model from the following link:
https://www.ti.com/lit/zip/snvm347
...

All of the files in that folder are either encrypted, or in a proprietary binary form. I cant see anything useful in them. The only way that they can be used is by using TI-TINA, which is nothing but a come-on for **broken link removed**.

I have been going out of my way to avoid designing with TI parts since they started doing this...

 

[alec_t]

Likewise. Makes you wonder what TI's thinking is re encrypting models. You'd think it would be in their interest to have open-source models so that a much bigger community, and hence more potential customers, would use them in designs.

 

[Mikebits]

All of the files in that folder are either encrypted, or in a proprietary binary form. I cant see anything useful in them. The only way that they can be used is by using TI-TINA, which is nothing but a come-on for **broken link removed**.

I have been going out of my way to avoid designing with TI parts since they started doing this...

Your right. I did not think to check that. I just saw Pspice but did not try to open it. My bad