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LTspice: SOAtherm Tutorial

Dan Eddleman - Senior Applications Engineer Oct 8th 2014

Verifying that a Hot Swap design does not exceed the capabilities of a MOSFET is a challenge at high power levels. Fortunately, thermal behavior and SOA may be modeled in circuit simulators such as LTspice IV® . The SOAtherm-NMOS symbol included in LTspice contains a collection of MOSFET thermal models developed by Linear Technology to simplify this task. These thermal models can be used to verify that the MOSFET maximum die temperature is not exceeded, even in the Spirito region where allowable current falls off exponentially at high drain-to-source voltages. In theory, SOAtherm reports the temperature of the hottest point on the MOSFET die. SOAtherm models predict the temperature of the MOSFET without influencing the electrical behavior of the circuit simulation. This video covers how to use the SOAtherm models distributed with LTspice and highlights how a circuit designer can easily evaluate the SOA requirements of an application and the suitability of the chosen N-channel MOSFET.

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Software

LTspice

LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice

To launch a ready to run LTspice demonstration circuit for this part:

  • Step 1: If you have not installed LTspice on this computer, download and install LTspice
  • Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
  • Step 3: If LTspice does not automatically open after clicking the link above, you can instead run the simulation by right clicking on the link and selecting "Save Target As." After saving the file to your computer, start LTspice and open the demonstration circuit by selecting 'Open' from the 'File' menu

To explore other ready to run LTspice demonstration circuits, please visit our Demo Circuits Collection.