11-22
M68040 USER’S MANUAL
MOTOROLA
11.9.4 With Heat Sink and Forced Air
In the specification provided by Thermalloy, Inc., a chart illustrates the air velocity versus
thermal resistance. This chart applies if airflow is used with the heat sink. Table 11-6 lists
the calculations based on this chart.
Table 11-6. Thermal Parameters with Heat Sink and Airflow
Thermal Mgmt.
Technique
Defined Parameters
Heat-Sink
Spec.
Calculated
MHz
Airflow Velocity
PD
TJ
θ
JC M AX .
θ
CA
θ
JA
TC
TA
MC68040
25
33
200 LFM
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0W
110
°C3 °C/W
4.25
°C/W
7.25
°C/W
91.1
°C
90.2
°C
84.2
°C
86.9
°C
86.0
°C
80.0
°C
64.3
°C
62.2
°C
47.7
°C
54.2
°C
52.0
°C
37.5
°C
25
33
400 LFM
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0W
110
°C3 °C/W
2.30
°C/W
5.25
°C/W
91.1
°C
90.2
°C
84.2
°C
86.9
°C
86.0
°C
80.0
°C
76.9
°C
75.4
°C
64.9
°C
69.6
°C
68.0
°C
57.5
°C
25
33
600 LFM
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0W
110
°C3 °C/W
1.50
°C/W
4.50
°C/W
91.1
°C
90.2
°C
84.2
°C
86.9
°C
86.0
°C
80.0
°C
81.7
°C
80.3
°C
71.3
°C
75.4
°C
74.0
°C
65.0
°C
25
33
800 LFM
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0W
110
°C3 °C/W
1.25
°C/W
4.25
°C/W
91.1
°C
90.2
°C
84.2
°C
86.9
°C
86.0
°C
80.0
°C
83.2
°C
82.0
°C
73.5
°C
77.3
°C
76.0
°C
67.5
°C
MC68LC040 and MC68EC040
20
25
33
200 LFM
4.0 W
5.0 W
6.3 W
110
°C3 °C/W
4.25
°C/W
7.25
°C/W
98.0
°C
95.0
°C
91.1
°C
81.0
°C
73.8
°C
64.3
°C
20
25
33
400 LFM
4.0 W
5.0 W
6.3 W
110
°C3 °C/W
2.30
°C/W
5.25
°C/W
98.0
°C
95.0
°C
91.1
°C
89.0
°C
83.8
°C
76.9
°C
20
25
33
600 LFM
4.0 W
5.0 W
6.3 W
110
°C3 °C/W
1.50
°C/W
4.50
°C/W
98.0
°C
95.0
°C
91.1
°C
92.0
°C
87.5
°C
81.7
°C
20
25
33
800 LFM
4.0 W
5.0 W
6.3 W
110
°C3 °C/W
1.25
°C/W
4.25
°C/W
98.0
°C
95.0
°C
91.1
°C
93.0
°C
88.8
°C
83.2
°C
