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Electrothermal Simulation
Specifying an Electrothermal Simulation
Alternative Syntax for External Definition
The thermal node can be defined external to the subcircuit definition. This means thermal
analysis can be used without modifying the structure of your design kits (schematics, symbols,
models). This is different to the internal definition where you can only define the thermal node
of a subcircuit by adding the command inside its definition.
You specify the .TEMPNODE SUBCKT=subckt THNODE=node external to the subcircuit
definition, not internal. It creates a thermal node named node in the subcircuit. Because it is an
internal node, the instantiations of the subcircuit do not need to change. Its hierarchical name
must be used to connect it to a thermal network.
Electrothermal Simulation Outputs
Additional outputs are available when using electrothermal simulation. You can easily plot the
dissipated power, the local time-varying temperature of the blocks, and the temperature
elevations. For example:
• Instantaneous power:
.plot tran pow(X1) pow(X2)
• Instantaneous temperature, in degrees Celsius:
.plot tran temp(X1) temp(X2)
• Temperature change (from the global temperature):
.plot tran V(th1) V(th2)
Electrothermal Simulation Modes
To select the accuracy of the electrothermal simulation, specify option ETMODE=0|1|2.
When ETMODE=1, default, Eldo makes the assumption that the temperature evolves at a
slower rate than electrical quantities to perform a faster simulation. When this assumption is
true (which is the case in real circuits), results are accurate. If this assumption is not true
(generally for ideal circuits), select ETMODE=2 to obtain accurate results. Specifying
ETMODE=0 deactivates electrothermal simulation.
Notes
• For internal definition syntax, there can be only one .TEMPNODE command per
.SUBCKT: all devices in a subcircuit share the same temperature node, hence the same
temperature.
• For internal definition syntax, the node specified on the .TEMPNODE command is
usually a node at the interface of the .SUBCKT definition, to connect a thermal network
between subcircuits. This is not mandatory: thermal devices can be connected from
outside using full-hierarchical names (for example R1 x1.x2.thn x1.x3.thn 1).
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Eldo® User's Manual, 15.3