MOSFET datasheet not lining up with SPICE simulation

H

HippopotamusXD

Newbie level 5
Joined
Sep 26, 2024
Messages
9
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
130
I'm trying to verify a MOSFET i plan on using in a design, it's a IMT40R025M2H ( https://www.infineon.com/dgdl/Infin...N.pdf?fileId=8ac78c8c8eeb092c018f84c54cec4d51 )

Diagram 16 shows V_GS as a function of the gate charge, and it shows that the plateau starts around 8V


I'm running a simple simulation in Altium Mixed Simulation SPICE simulator which looks like this


And this is the graph I'm getting, which shows the plateau at around 15V. I know the scale is wrong, as the datasheet shows V_GS in relation to gate charge and my graph is in relation to time, but the start of the plateau should be at the same voltage regardless. The datasheet measurement is done at V_DD = 200V, and I_D = 15.7A, which would make the plateau voltage higher, so I'd expect my simulation, with drain and source short circuited, would have an even lower plateau voltage. Red is the pulse source voltage, and yellow is voltage between gate and ss pins.


What I also find strange is the voltage curve at turn-off, where it looks as if the plateau voltage is around 4V

Is the datasheet wrong or am I just misreading the graph?
 

Sort by date Sort by votes
Hi,

at first I have to say: better trust the datasheet than any simulation.

But:
to compare test results you need to use the identical test setup.

* You used shorted Drain with Source
* But datasheet says: 200V and 15.7A and test setup according JEP192.
--> This is not the same at all.

I don´t know the test setup used by JEP192 ... (if you want to compare .. it´s your job to get the according informations)

Klaus
 

Upvote 0 Downvote
KlausST said:
* You used shorted Drain with Source
* But datasheet says: 200V and 15.7A and test setup according JEP192.
--> This is not the same at all.
Click to expand...

I ran a simulation with V_DD = 200V and a 12 Ohm resistor in series to simulate the I_D = 16A and got the same graph, only difference being that the plateau voltage is 0.3V higher (as expected because of higher V_DD) and last a bit longer (as expected because of higher I_D)



Also ran a sweep on the gate resistor value, from 1 to 10 Ohm, and got plateau voltage of around 8V for 10 Ohm, but the datasheet setup used 1.8 Ohm


I know I should trust the datasheet values more, but I'm trying to calculate switch on losses, and a lot of resources I found stated that simulations are more accurate because of the nonlinear capacitances in the mosfet, making analytical solutions inaccurate, so as a first step i wanted to verify the simple things in simulations first and got caught up on this.
 

Upvote 0 Downvote
Hi,

HippopotamusXD said:
I ran a simulation with V_DD = 200V and a 12 Ohm resistor in series to simulate the I_D = 16A
Click to expand...

I can´t find any information in the datasheet that they used a 12 Ohms resistor.
All I can see they used 15.7 A ... and I guess they did it this way.
It´s not the same!

Again: please look up JEP192!

Example:
While increasing V_GS ... R_DS decreases.
* With a 12Ohms resistor as load: V_DS = 200V * R_DS / (R_DS + 12 Ohms)
* With a 15.7A crrent source: V_DS = 15.7A * R_DS (limited by 200V)
--> V_DS follows different rules ... and due to the miller capacitance V_DS will influence V_GS behaviour. So it´s quite expectable to get different results.

Klaus
 

Upvote 0 Downvote
A difference could be the Vgs(th) in the sim model may be different than the value used in the data sheet plot.
Can you look at the sim model and see its value, or do a sim to determine Vgs(th) (curve in Diagram 11)?
 

Upvote 0 Downvote
You must log in or register to reply here.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…