# How to Obtain the formula for Thermal descrption when I have all data and graph (Eon(v,i,T,E,Rg))?

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Hello,

Your question is not very clear- are you saying you have developed a full Turn-on Loss table and would like to additionally include gate-resistance dependence behavior for which you have a graph for how E_on varies with Rg_on? If so, you need to generate a custom equation for the curve if it is not given, and this may require using a tool such as Excel. Can you link to or reference a specific device?

Kris
answered May 20, 2020 by (1,619 points)

I am facing negative turn on loss in my simulation so I need to generate a formula for turn on and off loss. how can I obtain it ?

i have linke the component below.https://www.infineon.com/dgdl/Infineon-F3L75R12W1H3_B27-DS-v03_02-EN.pdf?fileId=5546d46145460399014564559a6f3fe3

Hello, in this case it would be very helpful if you could post your model and the thermal description that you created. The error message says that a negative loss is being calculated so you should look at your lookup table data and ensure that the calculated losses cannot be less than zero; since we use interpolation/extrapolation it may be useful to include a vector of 0J loss values at both 0A and -1A, for example, unless you are modeling third quadrant losses, and therefore you need to specify positive losses for all negative current column values.
Hello,

Even though including  a vector of 0J loss values at both 0A and -1A I am still geting Error at lower temperature.Where in the datasheet there is no relationship of switching losses given with respect to Temperature.

linked the error and thermal description below.
Hello,

I have taken a look at the data sheet, and you are correct that the vendor only provides Esw values at 125C and 150C. Since you are operating the device (at least initially) at ~50C, the data is clearly being extrapolated to this lower temperature, and it's therefore recommended that you add loss data for another temp, e.g. 25 or 50C, to bound the operating temperature. You can do a hand-waving estimate, e.g., Eon@25C = 0.8*Eon@125C, linearly extrapolate the data yourself, or request this additional data/behavior from the manufacturer. Also, since the current value you are operating at is also below the lower limit of the provided data at 5A, I'd recommend you manually add an approximated set of loss data at say 1A. I hope this helps!

Kris