LM2678 Adjustable Pspice model

Scott,

The "knowledge" is in the comments of the model file:

* GM1 VALUES --> ADJ=0.673M, 3.3V - 0.48M, 5V - 0.673M, 12V - 1.54M
* Assume either ILIM or ONOFF exclusively

I believe that if you change the GM1 value to 0.673m the model should work with the ADJ configuration.

GM1 GND 15 EA1 REFV 4.8E-4

Should become:

GM1 GND 15 EA1 REFV 6.73E-4

 

Hi Britt,

Sorry for the late reply and thanks for that info, I did try that before but perhaps I was executing it wrong, I'll give it a more in-depth look!

Regards,

Gmore

Hi Britt/Other people who can help

I tried following your advice but I seem to be getting a solid 11V output. This is regardless of altering the external resistances, inductors or capacitors.

Changing the above parameters seems to only alter the transient over shoot or settling time.

Is there anything else you could suggest, thanks in advance.

Regards,

Gmore

Gmore,

A couple more questions for my reference only.

1.) Are you using PSpice and the reference design that was provided?

2.) What current load and Vin are you using?

I have run the model a few times for different voltages (inputs and outputs) and it does not appear to be working as I would expect it to. I will have to take a closer look at the model to see if there is any way to make it work for the ADJ case. Right now, I would only feel comfortable with this model for the 3.3V case.

1) I am using Pspice and I have tried it on both a web bench design and a design based off the parameters given in the technical document.

2) Load is purely resistive 100 ohms and Vin is 12v,

Also note my desired output is 6v for right now with the chance I might need it to be variable later on which is why I chose this chip.

Thanks heaps for trying if you can figure it out that would be great. 

Hey Britt,

I really appreciate that, thanks for all your hard work. I look forward to going through the code and finding out where I went wrong!, Thanks again.

Regards,

Scott