20
Tyco Electronics Corp.
Advance Data Sheet
March 2000
36 to 75 Vdc Input, 3.6, 3.3, 2.5, 2.0, or 1.8 Vdc Output; 180 W to 330 W
FW330 Power Modules: dc-dc Converters;
Thermal Considerations (continued)
Heat Transfer with Heat Sinks (continued)
Figures
32 and
33 can be used to predict which heat
sink a module will require in a natural convection envi-
ronment.
For example when a module is transversely oriented in
a 20 °C ambient and dissipates 50 W, then a 1.5 in.
heat sink is required.
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 29. Case-to-ambient thermal resis-
tance vs. airow for various heat sink congurations is
obtained by experimental testing of heat sinks, which
are offered in the product catalog.
8-2610 (C)
Figure 34. Case-to-Ambient Thermal Resistance
Curves; Transverse Orientation
8-2611(C)
Figure 35. 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.
The module used to collect the data in Figures
34 and
35 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.
Figures
37 through
40 show typical heat dissipation for
a range of output currents and three voltages for the
FW330 modules.
8-3016 (F)
Figure 36. FW330S3R671-56 Power Dissipation vs.
Output Current at 25 °C
θca
TC max
,
PD
---------------------
TC
TA
–
()
PD
------------------------
==
3.5
1.0
0.0
2.0
3.0
4.0
0.5
1.5
2.5
1.0
(200)
2.0
(400)
3.0
(600)
0.0
(0)
AIR VELOCITY, m/s (ft./min.)
NO HEAT SINK
1/4 IN. HEAT SINK
1/2 IN. HEAT SINK
1 IN. HEAT SINK
1 1/2 IN. HEAT SINK
RESISTANCE,
Θ
CA
(
°CW)
3.5
1.0
0.0
2.0
3.0
4.0
0.5
1.5
2.5
1.0
(200)
2.0
(400)
3.0
(600)
0.0
(0)
AIR VELOCITY, m/s (ft./min.)
NO HEAT SINK
1/4 IN. HEAT SINK
1/2 IN. HEAT SINK
1 IN. HEAT SINK
1 1/2 IN. HEAT SINK
RESISTANCE,
Θ
CA
(
°CW)
90
70
60
50
40
30
20
10
0
91929394959697989
99
80
OUTPUT CURRENT, IO (A)
POWER
DISSIPATION,
P
D
(W)
VI = 75 V
VI = 36 V
VI = 48 V