Author Topic: Help with modeling BA728 op amp in LTspice  (Read 347 times)

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Offline jj5Topic starter

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Help with modeling BA728 op amp in LTspice
« on: May 22, 2024, 06:09:13 am »
Hi there. I am trying to model a BA728 op amp in LTspice. The problem is that there are 730 op amps to choose from, and a BA728 isn't one of them. Some op amps which look like maybe good candidates are:

  • opamp.asy
  • opamp2.asy
  • UniversalOpAmp.asy
  • UniversalOpAmp1.asy
  • UniversalOpAmp2.asy
  • UniversalOpAmp3.asy
  • UniversalOpAmp3a.asy
  • UniversalOpAmp3b.asy
  • UniversalOpAmp4.asy

Can someone make a suggestion?
 

Offline magic

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Re: Help with modeling BA728 op amp in LTspice
« Reply #1 on: May 22, 2024, 08:36:42 am »
LTspice built-in models are mostly limited to LT's (and now AD's) own chips.

LTspice can also run many universal SPICE models which are sometimes released by manufacturers. So you may want to check if there is a BA728 model available from ROHM.

If not, look up instructions how to configure the various "universal opamp" models in LTspice. They differ in how complex they are and how many parameters can be modeled, pick something depending on your needs.

The chip itself appears to be very similar to the common LM358, but with a class AB output stage.
 
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Offline Zero999

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Re: Help with modeling BA728 op amp in LTspice
« Reply #2 on: May 22, 2024, 09:55:25 pm »
What's the BA728 doing?

You need to consider the important parts of the model:

To name a few:
Gain bandwidth product.
Slew-rate.
Output voltage limit.
Open-loop gain.
Phase margin.
Input impedance.

I would go for UniversalOpAmp2.asy.

I've looked at the data sheet and this is what I would do. I've not modelled the noise, which would require some guesswork.
 
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Offline jj5Topic starter

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Re: Help with modeling BA728 op amp in LTspice
« Reply #3 on: May 23, 2024, 02:54:44 am »
What's the BA728 doing?

I am building this.
 

Offline magic

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Re: Help with modeling BA728 op amp in LTspice
« Reply #4 on: May 23, 2024, 07:25:37 am »
If you just want to see how this circuit works, any ideal opamp model would do.

Or you could try LT1013, which is another "improved LM358", available in LTspice.
« Last Edit: May 23, 2024, 07:28:42 am by magic »
 
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Offline Zero999

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Re: Help with modeling BA728 op amp in LTspice
« Reply #5 on: May 24, 2024, 09:44:41 pm »
It's not that important.

For completeness, here's National Semiconductor's LM358 model, entered into LTSpice.
 
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