Datasheet

LTM4614
12
4614fb
Figure 7. 1.2V No Heat Sink (V
IN
= 5V)
Figure 8. 1.2V Heat Sink (V
IN
= 5V)
applicaTions inForMaTion
Figure 9. 3.3V No Heat Sink (V
IN
= 5V) Figure 10. 3.3V Heat Sink (V
IN
= 5V)
4.5
2.0
3.0
3.5
4.0
2.5
1.0
1.5
0.5
0
4614 F07
11050 60 70 80 90 12010040
AMBIENT TEMPERATURE (°C)
LOAD CURRENT (A)
200LFM NO HEAT SINK
0LFM NO HEAT SINK
400LFM NO HEAT SINK
4.5
2.0
3.0
3.5
4.0
2.5
1.0
1.5
0.5
0
4614 F08
11050 60 70 80 90 12010040
0LFM HEAT SINK
200LFM HEAT SINK
400LFM HEAT SINK
AMBIENT TEMPERATURE (°C)
LOAD CURRENT (A)
4.5
2.0
3.0
3.5
4.0
2.5
1.0
1.5
0.5
0
4614 F09
11050 60 70 80
AMBIENT TEMPERATURE (°C)
90 12010040
0LFM NO HEAT SINK
200LFM NO HEAT SINK
LOAD CURRENT (A)
400LFM NO HEAT SINK
4.5
2.0
3.0
3.5
4.0
2.5
1.0
1.5
0.5
0
4614 F10
11050 60 70 80 90 12010040
AMBIENT TEMPERATURE (°C)
LOAD CURRENT (A)
0LFM HEAT SINK
200LFM HEAT SINK
400LFM HEAT SINK
module temperature rise can be allowed. As an example, in
Figure 7 the load current is derated to 3A for each channel
with 0LFM at ~ 90°C and the total combined power loss for
both channels at 5V to 1.2V at 3A output is ~1.5 watts. If
the 90°C ambient temperature is subtracted from the 120°C
maximum junction temperature, then the difference of
30°C divided by 1.5W equals a 20°C/W thermal resistance.
Table 2 specifies a 15°C/W value which is close. Table 2
and Table 3 provide equivalent thermal resistances for
1.2V and 3.3V outputs with and without air flow and
heat sinking. The combined power loss for the two 4A
outputs can be summed together and multiplied by the
thermal resistance values in Tables 2 and 3 for module
temperature rise under the specified conditions. The
printed circuit board is a 1.6mm thick four layer board
with 2 ounce copper for the two outer layers and 1 ounce
copper for the two inner layers. The PCB dimensions are
95mm × 76mm. The data sheet lists the θ
JA
(junction to
ambient) and θ
JC
(junction to case) thermal resistances
under the Pin Configuration diagram.