Lucent Technologies Inc.
13
Data Sheet
May 2000
dc-dc Converters; 36 to 75 Vdc Input, 5 Vdc Output; 50 W and 75 W
QW050A1 and QW075A1 Power Modules:
Thermal Considerations
(continued)
Heat Transfer Without Heat Sinks
(continued)
8-2306 (C).a
Figure 25. Forced Convection Power Derating with
No Heat Sink; Either Orientation
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 attach 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 a larger hole is used, the mounting
torque from the pin side must not exceed 0.25 N-m
(2.2 in.-lbs.).
Thermal derating with heat sinks is expressed by using
the overall thermal resistance of the module. Total mod-
ule thermal resistance (
θ
ca) is defined as the maximum
case temperature rise (
T
C, max
power dissipation (P
D
):
) divided by the module
The location to measure case temperature (T
shown in Figure 22. Case-to-ambient thermal resis-
tance vs. airflow is shown, for various heat sink config-
urations, heights, and orientations, as shown in
Figures 26 and 27. Longitudinal orientation is defined
as the long axis of the module that is parallel to the air-
flow direction, whereas in the transverse orientation,
the long axis is perpendicular to the airflow. These
curves were obtained by experimental testing of heat
sinks, which are offered in the product catalog.
C
) is
8-2107 (C)
Figure 26. Case-to-Ambient Thermal Resistance
Curves; Transverse Orientation
8-2108 (C)
Figure 27. Case-to-Ambient Thermal Resistance
Curves; Longitudinal Orientation
10
20
30
40
50
60
0
10
LOCAL AMBIENT TEMPERATURE, T
A
(
°
C)
5
20
100
0
15
4.0 m/s (800 ft./min.)
P
D
70
80
90
θ
ca
T
C max
P
D
,
---------------------
T
C
------------------------
T
A
–
(
)
P
D
=
=
0.5
(100)
1.5
(300)
2.0
(400)
2.5
(500)
3.0
(600)
NAT
CONV
1.0
(200)
0
9
7
6
8
11
10
5
4
3
2
1
R
C
°
C
C
1 IN. HEAT SINK
1/2 IN. HEAT SINK
NO HEAT SINK
1/4 IN. HEAT SINK
AIR VELOCITY, m/s (ft./min.)
0.5
(100)
1.0
(200)
1.5
(300)
2.0
(400)
2.5
(500)
0
9
AIR VELOCITY, m/s (ft./min.)
7
6
8
11
10
3.0
(600)
NAT
CONV
5
4
3
2
1
1 IN. HEAT SINK
1/2 IN. HEAT SINK
NO HEAT SINK
1/4 IN. HEAT SINK
R
C
°
C
C