Datasheet
IBM PowerPC 750GX RISC Microprocessor
DD1.X
System Design Information
750GX_ds_body.fm SA14-2765-02
September 2, 2005
Typical die-junction temperatures (T
J) should be maintained less than the value specified in Table 3-3, depends upon the ambient inlet air temperature and the air temperature rise within the computer cabinet. An
electronic cabinet inlet-air temperature (T
A) may range from 30
°C to 40°C. The air temperature rise within a
cabinet (T
R) may be in the range of 5
°Cto 10°C. The thermal resistance of the interface material (θ
INT) is typi-
cally about 1
°C/W. Assuming a T
A of 30
°C, a T
R of 5
°C, a CBGA package θ
JC = 0.1, and a power dissipation
(P
D) of 10 watts, the following expression for TJ is obtained.
Die-junction temperature: T
J = 30
°C + 5°C + (0.1°C/W +1.0°C/W + θ
SA)
× 10 W
As an example heat sink, the heat-sink-to-ambient thermal resistance (
θ
SA) versus air flow velocity is shown in
Assuming an air velocity of 1.0 m/s, we have an effective
θ
SA of 5.8
°C/W, thus
T
J = 30
°C + 5°C + (0.1°C/W +1.0°C/W + 5.8°C/W) × 10 W,
resulting in a junction temperature of approximately 104
°C, which is within the maximum operating
temperature of the component in this example.
Heat sinks offered by companies such as Chip Coolers, IERC, Aavid Thermalloy, and Wakefield Engineering
offer different heat-sink-to-ambient thermal resistances, and may or may not need air flow.
Figure 5-10. Example of a Pin-Fin Heat-Sink-to-Ambient Thermal Resistance versus Airflow Velocity
Approach Air Velocity (m/s)
Heat
-S
ink
T
her
mal
Resist
ance
(
×°
C/W
)
1
2
3
4
5
6
7
8
0
0.5
1
1.5
2
2.5
3
3.5
Example Pin-Fin Heat Sink
(25
× 28 × 15 mm)