Datasheet
LTM4627
19
4627fc
For more information www.linear.com/LTM4627
Figure 7. 1.2V
OUT
Power Loss at 25°C Figure 8. 3.3V
OUT
Power Loss at 25°C
0
0.5
1.5
4627 F07
2.0
3.0
2.5
1.0
0
1 2 3 4 5 6 87 9 10 11 12 13 14 15
POWER LOSS (W)
OUTPUT CURRENT (A)
5V
IN
TO 1.2V
OUT
POWER LOSS
12V
IN
TO 1.2V
OUT
POWER LOSS
0
1
3
4627 F08
4
6
5
2
0
1 2 3
4 5 6 7 8 9 10 11 12 13 14 15
POWER LOSS (W)
OUTPUT CURRENT (A)
5V
IN
TO 3.3V
OUT
POWER LOSS
12V
IN
TO 3.3V
OUT
POWER LOSS
APPLICATIONS INFORMATION
Figure 10. 5V
IN
to 1.2V
OUT
with Heat Sink
0
2
6
4627 F10
8
16
14
12
10
4
0 LFM
200 LFM
400 LFM
40
50 60 70 80 90 100 110 120 130
AMBIENT TEMPERATURE (°C)
OUTPUT CURRENT (A)
Figure 9. 5V
IN
to 1.2V
OUT
No Heat Sink
0
2
6
4627 F09
8
16
14
12
10
4
0 LFM
200 LFM
400 LFM
5040 60 70 80 90 100 110 120 130
AMBIENT TEMPERATURE (°C)
OUTPUT CURRENT (A)
Figure 11 the load current is derated to ~12A at ~80°C with
no air or heat sink and the power loss for the 12V to 1.2V
at 12A output is about 2.8W. The 2.8W loss is calculated
with the ~2.35W room temperature loss from the 12V to
1.2V power loss curve at 12A, and the 1.2 multiplying
factor at 80°C ambient. If the 80°C ambient temperature
is subtracted from the 120°C junction temperature, then
the difference of 40°C divided by 2.8W equals a 14°C/W
θ
JA
thermal resistance. Table 2 specifies a 13°C/W value
which is very close. Table 2 and Table 3 provide equivalent
thermal resistances for 1.2V and 3.3V outputs with and
without airflow and heat sinking. The derived thermal
resistances in Tables 2 and 3 for the various conditions can
be m
ultiplied 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 multipli
-
cative factors. The printed circuit board is a 1.6mm thick
fo
ur layer board with two ounce copper for the two outer
layers and one ounce copper for the two inner layers. The
PCB dimensions are 95mm × 76mm. The BGA heat sinks
are listed in Table 4.