SOAtherm Tutorial

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 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.

Recommendations for Further Reading:

LTspice: Modeling Safe Operating Area Behavior of N-channel MOSFETs
LTC4226 Parallel MOSFETs in Hot Swap Circuits
LTspice SOAtherm Support for PCB and Heat Sink Thermal Models