Sauna V5.60 with Co-simulation Export

Sauna thermal model incorporated within LTspice circuit

Why export a thermal model to SPICE for co-simulation?

• Many electrical component properties are temperature-dependent
  • resistance, including MOSFET R_ds-on
  • gain
  • power dissipation
• Incorporating a thermal model in the SPICE analysis provides for a complete simulation under real world operating conditions
• Unlock the value of a thermal model
  • you can do much more than simply checking if Tjunct-max is exceeded
• With a thermal model in a SPICE simulation, accurately simulate circuit performance for:
  • startup
  • duty cycles
  • thermal runaway
  • voltage spikes
  • thermal coupling effects
  • thermal changes everything

Sauna is the ideal tool for generating and exporting a thermal model

• Sauna is based on the intuitive thermal resistor and thermal capacitor method
• No need to be a thermal analysis expert, 50% of users are electrical engineers
• Create models for heat sinks, boards and complete boxes
• Handles natural and forced convection and provides sophisticated radiation analysis
• Sauna models are compact, so the circuit simulation is not strongly impacted by additional complexity

Sauna export capability explained

• Easy to use
  • calculate temperatures within Sauna first, which initializes all the resistances
  • export only takes a second or two
• Can export a single thermal circuit or a library
• Create library with different cooling configurations
  • different component layouts
  • natural vs. forced air cooling
  • different heat sink sizes
  • metal vs. plastic boxes
• Component (heat source) options
  • no limit on the number of heat sources
  • do not have to model every heat source
  • use distributed wattage to include heat load from non-critical components
• Thermal model symbol is exported with thermal circuit
  • SPICE schematic only shows a simple block symbol
  • details of subcircuit are hidden
  • only connection points are heat sources and ambients

Thermal model symbol within LTspice
 

SPICE versions supported

• Directly supports LTspice
  • widely used industry standard
  • free download from Analog Devices
• Works with other SPICE versions as well, including PSPICE
  • if not using LTspice, some user manipulation may be required, such as creating a symbol for the thermal circuit
• For co-simulation effect, need thermally enhanced component SPICE models
  • thermally enhanced models available from Infineon, On Semi, Analog Devices, more
  • some component models, particularly for older components, are not thermally enhanced
  • can mix thermally enhanced and non-enhanced components in the co-simulation

Additional V5.6 feature: gap resistor improvement

• Can specify a special gap distance
• Provides modeling flexibility
• Can use for simplifying models for export

Easily combine ambients

Additional V5.6 feature: combine ambient tool

• When modeling, can somtimes create more ambients than necessary
• New feature makes it easy to combine multiple fixed node ambients into a single ambient
• Reduces clutter, model is easier to understand

Updated Sauna evaluation package

• Best way to learn about Sauna is to try the free evaluation package.
• Evaluation package now includes a co-simulation export sample problem. (LTspice required for co-simulation, free software.)
• To get the evaluation package, go to Sauna evaluation package download.