GX1 Datasheet, PDF (207/247 Pages) National Semiconductor (TI) – Processor Series Low Power Integrated x86 Solution

7.0 Package Specifications
The thermal characteristics and mechanical dimensions for
the Geode GX1 processor are provided on the following
pages.
7.1 THERMAL CHARACTERISTICS
Table 7-1 shows the junction-to-case thermal resistance of
the SPGA and BGA package and can be used to calculate
the junction (die) temperature under any given circum-
stance.
Table 7-1. Junction-to-Case Thermal Resistance
for SPGA and BGA Packages
Package
θ_JC
SPGA
BGA
1.7 °C/W
1.1 °C/W
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 (see Table 6-4 on page 190). As long as the
case temperature of the device is maintained within this
range, the junction temperature of the die will also be main-
tained within its allowable operating range. However, the
die (junction) temperature under a given operating condi-
tion can be calculated by using the following equation:
T_J = T_C + (P * θ_JC)
where:
T_J = Junction temperature (°C)
T_C = Case temperature at top center of package (°C)
P = Maximum power dissipation (W)
θ_JC = Junction-to-case thermal resistance (°C/W)
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.
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 max-
imum ambient temperature:
where:
θ_CS + θ_SA = -^T---^C------_P^–-----T----^A--
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 = -^T---^C------_P^–-----T----^A--
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 7-2 on
page 208) represents the maximum allowed thermal resis-
tance of the selected cooling solution which is required to
maintain the maximum T_C (shown in Table 6-4 on page
190) for the application in which the device is used.
Revision 1.0
207
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