GXLV Datasheet, PDF (207/247 Pages) National Semiconductor (TI) – Geode™ GXLV Processor Series Low Power Integrated x86 Solutions

7.0 Package Specifications
The thermal characteristics and mechanical dimensions
for the Geode GXLV 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 calcu-
late the junction (die) temperature under any given cir-
cumstance.
Table 7-1. Junction-to-Case Thermal Resistance
for SPGA and BGA Packages
Package
SPGA
BGA
θ_JC
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 T_C in Table 6-4 on page 189). As long
as the case temperature of the device is maintained within
this range, the junction temperature of the die will also be
maintained within its allowable operating range. However,
the die (junction) temperature under a given operating
condition can be calculated by using the following equa-
tion:
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
maximum 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)
represents the maximum allowed thermal resistance of
the selected cooling solution which is required to maintain
the maximum T_C (shown in Table 6-4 on page 189) for the
application in which the device is used.
Revision 1.1
207
www.national.com