APPLICATION NOTE
6
Suppose that a resistor's resistance multiplier is unity when measured at 0
ο
C. To signify
this, T_MEASURED can be specified in the resistor's corresponding .MODEL statement as
.MODEL RMOD RES(R=1, TC1=0.0001, T_MEASURED=0)
When the circuit is operating at 0
ο
C, R evaluates to 1. At 100
ο
C, R evaluates to 1.01 which is the
resistance multiplier (R=1) plus the first order operational temperature effect (TC1 * (TEMPT_
MEASURED)).
T_ABS allows specification of an absolute device temperature. If T_ABS is specified as T_ABS=25, the
model is held at 25
ο
C no matter what the circuit's operational temperature is doing. Adding T_ABS=25 to
the model definition causes R to evaluate to 1.0025 at all times, even if the operational temperature is
varied within parametric or DC sweep analyses.
T_REL_GLOBAL is used to specify a device temperature that is relative to the circuit's operational
temperature. For example, a power resistor might be dissipating power and be warmer than its
surrounding global ambient by 10
ο
C. This can be specified in a .MODEL statement as
.MODEL Rbreak RES (R=1, TC1=0.001, T_REL_GLOBAL=10)
T_REL_LOCAL is used in the AKO ("a kind of") .MODEL statement. An AKO model references an
existing model, thus inheriting the existing model's parameter definitions. Parameter values can be
overridden or added by specifying them in the AKO .MODEL statement. Using this technique, the device
temperature defined in a new model can be calculated relative to the absolute device temperature
specified in a base model. The base model must define the absolute device temperature using
the T_ABS parameter. The AKO model must define the relative change to the T_ABS temperature using
the T_REL_LOCAL parameter.
For example, a model, RMOD, whose device temperature is 117
ο
C greater than that specified in
the RBASE model statement can be defined as
Figure 4: Circuit to understand Temperature Effects on Passive Components
