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PHYSICAL DESIGN AND DEBUGGING
Series
Termination
Figure 11-27. Star Connectipn
11.7 THERMAL CHARACTERISTICS
231732i11-27
The thermal specification for the Inte1386 DX microprocessor defines the maximum case
temperature. This section describes
how
to ensure that an Intel386 DX microprocessor
system meets this specification.
Thermal specifications for the Intel386 DX microprocessor are designed to guarantee a
tolerable temperature at
the.
surface of the Inte1386 DX microprocessor chip. This tem-
perature (called the junction temperature) can be determined from external measure-
ments using the known thermal characteristics of the package. Two equations for
calculating junction temperature are
as
follows:
where
T
j
= junction temperature
a
= ambient temperature
Te
= case temperature
Sja
= junction-to-ambient temperature coefficient
Sje
= junction-to-case temperature coefficient
PD = power dissipation (worst-case
Icc
*
Vee)
11-32