Spice model

hitee007

Hi Colleagues,

Could you please let me know how to adjust the Vth of SiC MOSFET spice models from Wolfspeed? I am trying to make simulation on paralleling connection with Vth variations.

Thanks in advance.

Best regards

Helong

Forum_Moderator

Thank you for your post, it has been approved and we will respond as soon as possible.

Bdeboi

Hi Helong,

The method for adjusting the Vth will depend on which simulator you are using. If you are using LTspice models, you can right-click the model symbol and define a 'Vths' parameter in the SpiceLine2 field:

If you are using any of the other simulator models, you'll need to edit the netlist directly. Open the appropriate .cir model file in a text editor, and find the '.SUBCKT MOSFET...' statement. Underneath you will see some .param statements, one of which is Vths. You can change the value of Vths here.

Increasing Vths will cause the die to conduct at a lower threshold voltage, decreasing Vths will cause the die to conduct at a higher threshold voltage.

In your model library download, there is a SPICE userguide that provides more information on how you can customize the model for your own needs.

Thanks,

Brian

hitee007

Hi Brian,

Thanks for the reply. I am using LTspice. Looks like that the solution directly changing Vths does not work for bare die and discrete device models.

Is it possible to adjust the Vth of bare die and discrete device models?

Thanks in advance.

Best regards

Helong

ZMiller

Hi Helong,

For discrete and bare die LTspice models, you can follow the process that I outlined in this previous forum post: https://forum.wolfspeed.com/discussion/comment/1030#Comment_1030

Please let me know if you have any issues.

Thanks,

Zack

hitee007

Hi Zack,

Thanks very much. It works.

I have a further question. With this solution, it can only define a fix Vth value. Is it possible to change the parameters in (e3 NET3 0 Value {Limit(-93.938n*V(Tjc)**3+27.548u*V(Tjc)**2-5.5921m*V(Tjc)+2.6741,0.8,3.5)}), for example, which could then also reflect the temperature impact?

My target is to make simulation as close to the real case as possible. With real Vth variations, the Vth of devices also depends on temperature. They just maybe, for example, have an offset or different temperature ratio.

Best regards

Helong

ZMiller

Hi,

You can definitely change the parameters in the equation. The equation is just a polynomial fit to existing Vth data points. If you want to change the equation, I'd recommend evaluating what you expect the Vth to be and fitting to those points versus temperature. You could also have a scaling equation that strictly modifies Vth based on a temperature scaling coefficient. Either way, changing the equation at e3 is the way to go.

Thanks,

Zack

hitee007

Thanks Zack. This question can be closed.

Best regards

Helong