Datasheet
DD2.X
PowerPC 750CL Microprocessor
Preliminary
In this example, let:
T = 105°C maximum
J
Ta = 50°C at heatsink = 35°C air inlet temperature plus 15°C internal temperature rise
Pd = 6 W maximum at 105°C
ꢀjc = 2°C/W
ꢀcs = 0.5°C/W
ꢀsa = unknown
So
105°C = 50°C + 6 W(2 + 0.5 + x°C/W)
Thus
ꢀsa ≤ 6.67°C/W
Airflow at the heatsink is a minimum of 1 m/s. Considering the heatsink of Figure 5-10, thermal resistance at
1 m/s airflow is less than 5.8°C/W, which satisfies the requirement with a reasonable engineering margin.
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)
System Design Information
Page 62 of 70
Version 2.5
December 2, 2008
IBM [ IBM ]
