Datasheet
LTM4649
19
4649f
For more information www.linear.com/LTM4649
Figure 9. 5V
IN
, 3.3V
OUT
and
1.5V
OUT
Power Loss
Figure 10. 12V
IN
, 3.3V
OUT
and 1.5V
OUT
Power Loss
APPLICATIONS INFORMATION
Figure 11. No Heat Sink with 5V
IN
to 1.5V
OUT
Figure 12. No Heat Sink with
12V
IN
to 1.5V
OUT
Figure 13. No Heat Sink with
5V
IN
to 3.3V
OUT
Figure 14. No Heat Sink with
12V
IN
to 3.3V
OUT
airflow or heat sinking in a properly define chamber. This
θ
JB
+ θ
BA
value is shown in the Pin Configuration sec-
tion and should accurately equal the θ
JA
value because
approximately 100% of power loss flows from the junc-
tion through the board into ambient with no airflow or top
mounted heat sink.
The 5V
IN
and 12V
IN
power loss curves in Figures 9 and10
can be used in coordination with the load current derating
curves in Figures 11 to 14 for calculating an approximate
θ
JA
thermal resistance for the LTM4649 with various
heat sinking and airflow conditions. The power loss
curves are taken at room temperature, and are increased
with a multiplicative factor according to the ambient
temperature. This approximate factor is: 1.4 for 120°C.
The derating curves are plotted with the output current
starting at 10A and the ambient temperature at 40°C. The
output voltages are 1.5V and 3.3V. These are chosen to
include the lower and higher output voltage ranges for
correlating the thermal resistance. Thermal models are
derived from several temperature measurements in a
controlled temperature chamber along with thermal mod-
eling analysis. The junction temperatures are monitored
LOAD CURRENT (A)
0
0
EFFICIENCY (%)
0.5
1.0
1.5
2.0
2.5
3.0
2 4 6 8
4649 F09
10
V
OUT
= 3.3V
V
OUT
= 1.5V
LOAD CURRENT (A)
0
0
EFFICIENCY (%)
0.5
1.0
1.5
2.0
2.5
3.0
2 4 6 8
4649 F10
10
V
OUT
= 3.3V
V
OUT
= 1.5V
AMBIENT TEMPERATURE (°C)
0
0
LOAD CURRENT (A)
2
4
6
8
12
20
40 60 80
4649 F11
100 120
10
400LFM
200LFM
0LFM
AMBIENT TEMPERATURE (°C)
0
0
LOAD CURRENT (A)
2
4
6
8
12
20
40 60 80
4649 F12
100 120
10
400LFM
200LFM
0LFM
AMBIENT TEMPERATURE (°C)
0
0
LOAD CURRENT (A)
2
4
6
8
12
20
40 60 80
4649 F13
100 120
10
400LFM
200LFM
0LFM
AMBIENT TEMPERATURE (°C)
0
0
LOAD CURRENT (A)
2
4
6
8
12
20
40 60 80
4649 F14
100 120
10
400LFM
200LFM
0LFM