SpeedFit™ Design Simulator
Simulate and evaluate the performance of SiC-based power circuits and determine the right SiC device in seconds.
Start a SimulationExternal thermal resistance yields strange result?
A customer reported that he's getting strange results in LTspice when connecting an external thermal resistance. Please see below.
The circuit works in above condition, reading ~78C for Tj and ~63C for Tc, which matches datasheet calculation. It also works for R2 value between 0-0.8.
However, if we change R2 value to 0.81, Tj suddenly reads 450C and Tc reads 280C, which makes no sense.
May I know what could be the reason for this?
Comments
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Nevermind, I found the problem... a thermal capacitance is needed, otherwise peak temp. will exceed model limit and trigger the error.
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Thank you for the inquiry, I'm glad to see that you got the simulation to work. However, a capacitor is not required on the Tj or Tc terminals. One may be added to model the thermal capacitance of the heatsink, but it is not required for the simulation to function properly. The Kelvin source connection, however, can lead to unexpected behavior if left floating as shown in your screenshot. If the model contains a kelvin source pin, it should be connected in order to accurately reflect the behavior of the device.
