EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: jj5 on May 22, 2024, 06:09:13 am

Title: Help with modeling BA728 op amp in LTspice
Post by: jj5 on May 22, 2024, 06:09:13 am
Hi there. I am trying to model a BA728 (https://www.alldatasheet.com/datasheet-pdf/pdf/36174/ROHM/BA728.html) 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:


Can someone make a suggestion?
Title: Re: Help with modeling BA728 op amp in LTspice
Post by: magic 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.
Title: Re: Help with modeling BA728 op amp in LTspice
Post by: Zero999 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.
Title: Re: Help with modeling BA728 op amp in LTspice
Post by: jj5 on May 23, 2024, 02:54:44 am
Quote from: Zero999 on May 22, 2024, 09:55:25 pm
What's the BA728 doing?

I am building this (https://www.jj5.net/file/2024-05-22-141448/).
Title: Re: Help with modeling BA728 op amp in LTspice
Post by: magic 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.
Title: Re: Help with modeling BA728 op amp in LTspice
Post by: Zero999 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.