Webench .TRAN parameters and 8 minute time limit

David,

The TPS54478 does have Bode Plot support for simulation in WEBENCH®. It is under the simulation window pulldown:

The simulations are limited to 8 minutes or less for socket timeouts in the internet protocals. If you need to actually run a simulation for 50ms, the best option would be to export your design to TINA-TI and run the simulation locally. You cna then adjust any of the parameters that you need to adjust.

The actual clock time for this length of simulation would probably be on the order of a couple of hours.

Thanks, the Bode plot would be nice but I don't have that drop down list. When i press the "Sim" button I get this:

Tried both Firefox and IE. Costs extra?! :-/

David,

The picture did not come through. No charge at all for the full features of WEBENCH®!

Did you edit the schematic using the Schematic Editor? If so, the only simulation available would be a startup simulation.

If you did not need to change the topology of the circuit, you do not need to use the Schematic Editor. You can change component values via the BOM or schematc by simply clicking on the component and choosing an alternate component.

If you did have to change the topology, you should still be able to export the design to TINA-TI.

You can also access the Bode Plot through the Charts button if you have not used the Schematic Editor. These charts and OpVals are updated when you change component values without having to run a simulation.

Oops apparently the editor can't handle pasting a picture even though it looked ok when editing. Here it is, uploaded:

I also tried opening the original TPS54478 webench design and there I do have a drop down menu with Bode as a choice. Strange, all my edits were plain passive components from your lists. Also a bit strange that I have the tab "Parameters" (with .TRAN parameters) but no such tab in original design.

Oh. Bummer. I need to change the schematic, we have e g type III compensation (and I couldn't find a way to change "QTY" so I had to add capacitors). So I can't use Webench then? Can I get Bode plots in Tina-TI?

David,

You used the Schematic Editor for your edits. If you click on the Edit button as shown in the previous post, you will get a window to ask to create a copy of the design before proceeding. If you click OK, the Schematic Editor is invoked and you design will show the Custom Design tag (in your picture, upper left corner). This takes you into the full simulator interface where you can change the topology of the circuit, add passive and active components and do some interesting manipulations as you would in a full simulator.

If you only want to change the values of components, start from the original design from the product folder where you input your conditions. Once the design is created, go to the schematic page and right click on the component you wish to change and select an alternate component (or you can do this from the BOM page as I showed previously). Once a component is changes, the OpVals and charts are updated and you can see the impact quickly on your perfromance. Once all of the updates are made, you can then run the simulation (Bode Plot, etc.) to verify your changes.

Both the Schematic Editor and WEBENCH® Power Designer use the same inteface for pasive component changes. If you do not use the Schematic Editor button, I believe you will be able to do want you want and see the results you were trying to obtain.

David,

There is a TINA-TI average reference design in the product folder that uses type 3 compensation. It can be found here:

http://www.ti.com/product/TPS54478/toolssoftware

Click on the Average Reference Design to download.

Thanks. I already tried importing the Webench design to Tina-TI and running it as-is (i e transient analysis) works. So I suppose I can at least run it for the required duration. A funny thing is that it doesn't use the normal source but a SUBCKT:

Regarding the average model, are you saying my present design, imported from Webench, won't work in Tina-TI for Bode plots? A bit surprising since it works for Bode plots in Webench normally. Guess I'll find out if I try. Otherwise I'll use the average model.

David,

For switching power supplies, you can not use the transient model to perform Bode Plots using standard spice techniques. This is due to the fact that you need to calculate the DC Bias point first to linearize the circuit for AC simulation. However since the circuit is switching, the DC Bias point can not be calculated by Spice. Hence we need a separate kind of model for AC simulations of switching power supplies. This is called an average model. In this model the switching nodes are averages out over a switching cycle so DC Bias point can be calculated. You can read up more about this in this FAQ.

Thanks,

Ok thanks then I understand. But I guess that means your Bode diagram only supports fsw=500kHz i e i can not add the 13,3k resistor to the schematic which changes mode to fsw=1MHz and thus I must use Tina TI?

Hi David,

Sorry for the inconvenience. We have recently introduced this feature called Sim Export and are in the process of enabling it for all the parts in WEBENCH. In order to see what features are enabled for what parts, you can refer to the following link

http://webench.ti.com/webench5/devices/

Also, if you go through the WEBENCH Panel from www.ti.com, you will come to the Visualizer Page which compares various solutions. There too all the features supported by each part are shown.

Thanks,