Analog Devices Linear ADI Power LTM4681 Manual page 71

APPLICATIONS INFORMATION
If the 60°C ambient temperature is subtracted from the
125°C junction temperature, then the difference of 65°C
divided by 12.8W yields a thermal resistance, θ
5°C/W—in good agreement with the value derived from
thermal simulation shown in the Pin Configuration sec-
tion. Table 10, Table 11 and Table 12 provide equivalent
thermal resistances for 0.9V, 1.5V, and 3.3V outputs with
and without airflow. The derived thermal resistances in
Table 10 through Table 12: Output Current Derating
Table 10. 0.9V Output
DERATING CURVE
Figure 38 to Figure 40
Figure 38 to Figure 40
Figure 38 to Figure 40
Table 11. 1.5V Output
DERATING CURVE
Figure 41 to Figure 43
Figure 41 to Figure 43
Figure 41 to Figure 43
Table 12. 3.3V Output
DERATING CURVE
Figure 44 to Figure 46
Figure 44 to Figure 46
Figure 44 to Figure 46
, of
JA
V (V) POWER LOSS CURVE
IN
5, 8, 12 Figure 35 to Figure 37
5, 8, 12 Figure 35 to Figure 37
5, 8, 12 Figure 35 to Figure 37
V (V) POWER LOSS CURVE
IN
5, 8, 12 Figure 35 to Figure 37
5, 8, 12 Figure 35 to Figure 37
5, 8, 12 Figure 35 to Figure 37
V (V) POWER LOSS CURVE
IN
5, 8, 12 Figure 35 to Figure 37
5, 8, 12 Figure 35 to Figure 37
5, 8, 12 Figure 35 to Figure 37
For more information
Table 10 through Table 12 for the various conditions can
be multiplied by the calculated power loss as a function
of ambient temperature to derive temperature rise above
ambient, thus maximum junction temperature. Room
temperature power loss can be derived from the efficiency
curves in the Typical Performance Characteristics sec-
tion and adjusted with the above ambient temperature
multiplicative factors.
AIRFLOW (LFM)
0
200
400
AIRFLOW (LFM)
0
200
400
AIRFLOW (LFM)
0
200
400
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LTM4681
HEAT SINK
(°C/W)
θ
JA
None 5
None 4
None 3
HEAT SINK (°C/W)
θ
JA
None 5
None 4
None 3
HEAT SINK (°C/W)
θ
JA
None 5
None 4
None 3
71
Rev. A