OPA310: PSpice model for OPA310S or OPA2310S (with shutdown)?

Hi Robert,

thanks for quickly replying on that!

Ok, I see. So no simulation model as of today. As for the turn-on and turn-off times, I believe that it's sufficient for my overall simulation model to model this with an ideal switch at the output with an according delay in the switching.

As for the impedance, the helpful document you did cite in the other thread (https://www.ti.com/lit/an/sboa367b/sboa367b.pdf) is stating that it should be modeled by placing a resistor and capacitor to ground according to the impedance specification provided by the data sheet. Do I get this right that this impedance has to be present only in the shutdown-state and not for regular operation? The same counts actually for the inputs and the parasitic capacitances as well, but my primary concern is the influence of the output.

Greetings,

Mario

Hello Robert,

Ok. Nonetheless it seems not really possible to simulate the overall behavior by adding some external switches and additional impedances. I was able to manage that somewhat, but not without some dirty side effects. Problem is that the feedback is broken when the output is disconnected.

So such complete simulations certainly require a direct support of the shutdown feature within the model.

Greetings,

Mario

Hi Mario,

That's one of the issues we faced when developing a shutdown model. The transient change between going to and from shutdown is difficult to model. 

Do you have any additional questions for me? 

Best Regards,

Robert Clifton 

Hi Robert,

I'm fine at the moment, I think.

Though, I did decide to walk around that matter by not using an OpAmp with shutdown at that place where I indended to do so initially. The point is that there is this fundamental issue that the OpAmp when brought up has to find it's operating state first. By definition, this is causing some "hickups" at the output. In some cases this might be tolerable, in some not.

Anyway, thanks for your input on that matter!

Regards,

Mario

Hi Mario,

Thank you!

The OPA310S datasheet does have the enable and disable output response shown. 

This should give a better idea of how it will behave in your system. Sadly, I don't think every device has these graphs in their datasheet. 

Best Regards,

Robert Clifton 

Hi Robert,

yes, in the particular case of the enable-operation you actually see the problem: The intended output voltage according to the inputs is 0V and is being achieved after approx. 1us. But until reaching these 0V the output will be forced to -2.75V for 1us. So in case the net the OpAmp attaches to is currently at 0V, it is assumed to stay there according to the input conditions. However, instead it will be temporarily pulled to -2.75V just after the output is going from high to low impedance when the OpAmp is getting enabled. This is the "hickup" as I called it. This is not nice and is a fundamental problem of OpAmps with shutdown. This can certainly only be fixed through zero-delays (certainly not possible) or black magic (I guess difficult too ). I was not aware about that pitfall before this discussion here. Nonetheless in many cases this issue can be surely tolerated.

Greetings,

Mario

Hi Mario,

Glad this was able to help you better understand the parts! 

Best Regards,

Robert Clifton