APPLICATION NOTE
5
Temperature Effects
Ambient
Passive component values can be subject to temperature effects that are dependent upon the circuit's
operational temperature. To account for these effects when simulating, each relevant component needs a
.MODEL statement specifying how the particular component value varies with temperature. The built-in
PSpice models for resistors, capacitors, and inductors have two temperature effect terms-linear and
quadratic. These terms may be curve fit to a component's actual temperature characteristics.
Resistors are not the only components with temperature effects; most capacitors, especially ceramics,
have very well-defined temperature curves depending on the dielectric used in their construction.
However, a single-slope temperature curve is not sufficient for simulating the most common types of
capacitors used in analog circuits. Therefore, both the linear and quadratic temperature coefficients must
be specified in their PSpice .MODEL statements, such as,
.MODEL X7R CAP (C=1, TC1=5.75E-5, TC2=-1.285E-5)
.MODEL Z5U CAP (C=1, TC1=2.38E-3, TC2=-1.48E-4)
Note: Resistors have an additional exponential temperature coefficient which can be used instead of the
linear and quadratic coefficients.
Per Component
In PSpice, the passive components can also be characterized for temperature effects that override the
circuit's operational temperature and the temperature, TNOM, at which model parameters are assumed
to have been measured. Individual device temperature behaviors can be customized by specifying either
the T_ABS, T_REL_GLOBAL, or T_REL_LOCAL parameter in a .MODEL statement. A new
measurement temperature can also be defined by setting the T_MEASURED model parameter.
You will simulate the circuit seen in Figure 4 to understand the temperature effects on passive
components.
