
Revision 3.1
195
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G
8.0
The thermal characteristics and mechanical dimensions
for the Geode GXm processor are provided on the follow-
ing pages.
Package Specifications
8.1 THERMAL CHARACTERISTICS
Table 8-1 shows the junction-to-case thermal resistance
of the SPGA and BGA package and can be used to calcu-
late the junction (die) temperature under any given cir-
cumstance.
Note that there is no specification for maximum junction
temperature given since the operation of both SPGA and
BGA devices are guaranteed to a case temperature range
of 0°C to 85°C. As long as the case temperature of the
device is maintained within this range, the junction tem-
perature of the die will also be maintained within its allow-
able
operating
range.
However,
temperature under a given operating condition can be cal-
culated by using the following equation:
the
die
(junction)
T
J
= T
C
+ (P *
θ
JC
)
where:
T
J
= Junction temperature (°C)
T
C
= Case temperature at top center of package (°C)
P = Power dissipation (W)
θ
J
C
= Junction-to-case thermal resistance (°C/W)
As stated previously, a maximum junction temperature is
not specified since a maximum case temperature is.
Therefore, the following equation can be used to calculate
the maximum thermal resistance required of the thermal
solution for a given maximum ambient temperature:
where:
θ
CS
= Max case-to-heatsink thermal resistance
(°C/W) allowed for thermal solution.
θ
SA
= Max heatsink-to-ambient thermal resistance
(°C/W) allowed for thermal solution.
T
A
= Max ambient temperature (°C)
T
C
= Max case temperature at top center of package
(°C)
P = Max power dissipation (W)
If thermal grease is used between the case and heatsink,
θ
CS
will reduce to about 0.01 °C/W. Therefore, the above
equation can be simplified to:
where:
θ
CA
=
θ
CS
= Max case-to-ambient thermal resistance
(°C/W) allowed for thermal solution.
The calculated
θ
CA
value (examples shown in Table 8-2)
represents the maximum allowed thermal resistance of
the selected cooling solution which is required to maintain
the 85°C case temperature for the application in which the
device is used.
These examples are given for reference only. The actual
value used for Maximum Power (P) and ambient tempera-
ture (T
A
) is determined by the system designer based on
system configuration, extremes of the operating environ-
ment, and whether active thermal management (via Sus-
pend Modulation) of the processor is employed.
Table 8-1. Junction-to-Case Thermal Resistance
for SPGA and BGA Packages
Package
θ
J
C
SPGA
1.7
°
C/W
1.1
°
C/W
BGA
θ
C
S
θ
S
A
+
---------------------
–
=
θ
CA
---------------------
–
=