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APPLICATIONS INFORMATION
140
120
100
80
60
40
0LFM
20
200LFM
400LFM
0
0
20
40
60
80
T
(°C)
AMB
Figure 44. 5V
to 0.7V
IN
Derating Curve, No Heat Sink
power loss curve at 84A (See Figure 37), with the 1.35
multiplying factor. If the 76°C ambient temperature is
subtracted from the 125°C junction temperature, then
the difference of °C divided by 12.56W yields a thermal
resistance, θ
, of ~4°C/W—in good agreement with the
JA
value derived from thermal simulation shown in the Pin
Configuration section. Table 10–Table 12 provide equiva-
lent thermal resistances for 0.4V, 0.6V and 0.7V outputs
with and without airflow.
Table 10. 0.4V Output
DERATING CURVE
Figure 38 to Figure 40
Figure 38 to Figure 40
Figure 38 to Figure 40
Table 11. 0.6V Output
DERATING CURVE
Figure 41 to Figure 43
Figure 41 to Figure 43
Figure 41 to Figure 43
Table 12. 0.7V Output
DERATING CURVE
Figure 44 to Figure 46
Figure 44 to Figure 46
Figure 44 to Figure 46
140
120
100
80
60
40
0LFM
20
200LFM
400LFM
0
100
120
0
20
4683 F44
Figure 45. 8V
OUT
Derating Curve, No Heat Sink
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
40
60
80
100
120
T
(°C)
AMB
4683 F45
to 0.7V
IN
OUT
Table 10– Table 12 for the various conditions can be multi-
plied 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 section and
adjusted with the above ambient temperature multiplica-
tive factors.
AIRFLOW (LFM)
0
200
400
AIRFLOW (LFM)
0
200
400
AIRFLOW (LFM)
0
200
400
www.analog.com
LTM4683
140
120
100
80
60
40
0LFM
20
200LFM
400LFM
0
0
20
40
60
80
T
(°C)
AMB
Figure 46. 12V
to 0.7V
IN
OUT
Derating Curve, No Heat Sink
HEAT SINK
θ
(°C/W)
JA
None
4.25
None
4
None
3
θ
HEAT SINK
(°C/W)
JA
None
4.25
None
4
None
3
HEAT SINK
θ
(°C/W)
JA
None
4.25
None
4
None
3
100
120
4683 F46
Rev. 0
71
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