Datasheet
IBM PowerPC 750GX RISC Microprocessor
DD1.X
Typical die-junction temperatures (TJ) should be maintained less than the value specified in Table 3-3,
Package Thermal Characteristics, on page 16. The temperature of the air cooling component greatly
depends upon the ambient inlet air temperature and the air temperature rise within the computer cabinet. An
electronic cabinet inlet-air temperature (TA) may range from 30°C to 40°C. The air temperature rise within a
cabinet (TR) may be in the range of 5°C to 10°C. The thermal resistance of the interface material (θINT) is typi-
cally about 1°C/W. Assuming a TA of 30°C, a TR of 5°C, a CBGA package θJC = 0.1, and a power dissipation
(PD) of 10 watts, the following expression for TJ is obtained.
Die-junction temperature: TJ = 30°C + 5°C + (0.1°C/W +1.0°C/W + θSA) × 10 W
As an example heat sink, the heat-sink-to-ambient thermal resistance (θSA) versus air flow velocity is shown in
Figure 5-10.
Figure 5-10. Example of a Pin-Fin Heat-Sink-to-Ambient Thermal Resistance versus Airflow Velocity
Example Pin-Fin Heat Sink
(25 × 28 × 15 mm)
8
7
6
5
4
3
2
1
0
0.5
1
1.5
2
2.5
3
3.5
Approach Air Velocity (m/s)
Assuming an air velocity of 1.0 m/s, we have an effective θSA of 5.8°C/W, thus
TJ = 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.
System Design Information
Page 68 of 73
750GX_ds_body.fm SA14-2765-02
September 2, 2005
IBM [ IBM ]
