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MC68LC040RC25A Datasheet, PDF (346/442 Pages) Freescale Semiconductor, Inc – M68040 Users Manual
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Freescale Semiconductor, Inc.
11.9.2 Forced Air
In this study, a small sample of MC68040 packages was tested in forced-air cooling in a
wind tunnel with no heat sink. The test was performed with approximately 6 W of power
being dissipated from within the package. As previously mentioned, since the variance in
θJA within the possible power range is negligible, it can be assumed for calculation
purposes that θJA is constant at all power levels. Using the previous equations, Table 11-3
lists the results of the maximum power dissipation at maximum θJC with airflow and no
heat sink for the MC68040, and Table 11-4 lists the results for the MC68LC040 and
MC68EC040. Refer to Table 11-1 for calculating other power dissipation values.
Table 11-3. Thermal Parameters with Forced Airflow
and No Heat Sink for the MC68040
MHz
25
25
25
33
33
33
25
25
25
33
33
33
25
25
25
33
33
33
25
25
25
33
33
33
25
25
25
33
33
33
Thermal Mgmt.
Technique
Airflow Velocity
100 LFM
250 LFM
500 LFM
750 LFM
1000 LFM
Defined Parameters
PD
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0 W
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0 W
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0 W
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0 W
6.3 W
6.6 W
8.6 W
7.7 W
8.0 W
10.0 W
TJ
110 °C
110 °C
110 °C
110 °C
110 °C
θJC
3 °C/W
3 °C/W
3 °C/W
3 °C/W
3 °C/W
Measured
Calculated
θJA
12.7 °C/W
11.0 °C/W
9.9 °C/W
9.5 °C/W
9.3 °C/W
θCA
9.7 °C/W
8.0 °C/W
6.9 °C/W
6.5 °C/W
6.3 °C/W
TC
91.1 °C
90.2 °C
84.9 °C
86.9 °C
86.0 °C
80.0 °C
91.1 °C
90.2 °C
84.2 °C
86.9 °C
86.0 °C
80.0 °C
91.1 °C
90.2 °C
84.2 °C
86.9 °C
86.0 °C
80.0 °C
91.1 °C
90.2 °C
84.2 °C
86.9 °C
86.0 °C
80.0 °C
91.1 °C
90.2 °C
84.2 °C
86.9 °C
80.0 °C
81.8 °C
TA
29.90 °C
26.18 °C
00.76 °C
12.21 °C
08.40 °C
00.00°C
40.70 °C
37.40 °C
15.40 °C
25.30 °C
22.00 °C
00.00 °C
47.63 °C
44.66 °C
24.86 °C
33.77 °C
30.80 °C
11.00 °C
50.15 °C
47.30 °C
28.30 °C
36.85 °C
34.00 °C
15.00 °C
51.41 °C
48.62 °C
30.02 °C
38.39 °C
17.00 °C
22.58 °C
11-18
M68040 USER’S MANUAL
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