14
Lineage Power
Data Sheet
April 2008
dc-dc Converters; 36 to 75 Vdc Input, 2.5 Vdc Output; 125 W to 150 W
FW250G1 and FW300G1 Power Modules:
Thermal Considerations (continued)
Heat Transfer Without Heat Sinks (continued)
8-2642 (C)
Figure 21. FW300G1 Power Dissipation vs. Output
Current at 25 °C
Heat Transfer with Heat Sinks
The power modules have through-threaded, M3 x 0.5
mounting holes, which enable heat sinks or cold plates
to be attached to the module. The mounting torque
must not exceed 0.56 N-m (5 in.-lb.). For a screw
attachment from the pin side, the recommended hole
size on the customer’s PWB around the mounting
holes is 0.130 ± 0.005 inches. If larger holes are used,
the mounting torque from the pin side must not exceed
0.25 N-m (2.2 in.-lb.).
Thermal derating with heat sinks is expressed by using
the overall thermal resistance of the module. Total mod-
ule thermal resistance (
θca) is dened as the maximum
case temperature rise (
TC, max) divided by the module
power dissipation (PD):
The location to measure case temperature (TC) is
shown in Figure 18. Case-to-ambient thermal resis-
tance vs. airow for various heat sink congurations is
sho
wn in Figures 22 and 23. These curves were
obtained by experimental testing of
heat sinks, which
are offered in the product catalog.
8-1321 (C)
Figure 22. Case-to-Ambient Thermal Resistance
Curves; Transverse Orientation
8-1320 (C)
Figure 23. Case-to-Ambient Thermal Resistance
Curves; Longitudinal Orientation
These measured resistances are from heat transfer
from the sides and bottom of the module as well as the
top side with the attached heat sink; therefore, the
case-to-ambient thermal resistances shown are gener-
ally lower than the resistance of the heat sink by itself.
23 had a thermal-conductive dry pad between the case
and the heat sink to minimize contact resistance.
To choose a heat sink, determine the power dissipated
as heat by the unit for the particular application. Figure
21 shows typical heat dissipation for a range of output
currents and three voltages for the FW300G1.
16
26
36
46
56
66
0
50
30
20
40
6
60
10
OUTPUT CURRENT, IO (A)
POWER
DISSIPATION,
P
D
(W)
VI = 75 V
VI = 48 V
VI = 36 V
θca
TC max
,
PD
---------------------
TC
TA
–
()
PD
------------------------
==
0.0
0.5
3.0
3.5
4.0
4.5
2.5
2.0
1.0
1 1/2 IN. HEAT SINK
1 IN. HEAT SINK
1/2 IN. HEAT SINK
1/4 IN. HEAT SINK
NO HEAT SINK
1.5
AIR VELOCITY, m/s (ft./min.)
0
0.5
(100)
1.0
(200)
1.5
(300)
2.0
(400)
2.5
(500)
3.0
(600)
CASE-TO-AMBIENT
THERMAL
RESISTANCE,
θCA
(
°C/W)
0
0.5
(100)
1.0
(200)
1.5
(300)
2.0
(400)
2.5
(500)
3.0
(600)
0.0
0.5
3.0
3.5
4.0
4.5
2.5
2.0
1.0
1 1/2 IN. HEAT SINK
1 IN. HEAT SINK
1/2 IN. HEAT SINK
1/4 IN. HEAT SINK
NO HEAT SINK
1.5
AIR VELOCITY, m/s (ft./min.)
CASE-TO-AMBIENT
THERMAL
RESISTANCE,
θCA
(
°C/W)