Lineage Power 13
Data Sheet
April 2008
36 to 75 Vdc Input, 3.3 Vdc Output; 33 W
QHW050F71 Power Modules; dc-dc Converters:
Thermal Considerations (continued)
Heat Transfer with Heat Sinks (continued)
8-2892(F)
Figure 23. Heat Sink Power Derating Curves;
1.0 m/s (200 lfm); 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 18 and
19 had a thermal-conductive dry pad between the case
and the heat sink to minimize contact resistance.
Custom Heat Sinks
A more detailed model can be used to determine the
required thermal resistance of a heat sink to provide
necessary cooling. The total module resistance can be
separated into a resistance from case-to-sink (θcs) and
sink-to-ambient (θsa) as shown in Figure 24.
8-1304(F).e
Figure 24. Resistance from Case-to-Sink and
Sink-to-Ambient
For a managed interface using thermal grease or foils,
a value of θcs = 0.1 °C/W to 0.3 °C/W is typical. The
solution for heat sink resistance is:
This equation assumes that all dissipated power must
be shed by the heat sink. Depending on the user-
defined application environment, a more accurate
model, including heat transfer from the sides and bot-
tom of the module, can be used. This equation pro-
vides a conservative estimate for such instances.
EMC Considerations
For assistance with designing for EMC compliance,
please refer to the FLTR100V10 Filter Module Data
Sheet (FDS01-043EPS).
Layout Considerations
Copper paths must not be routed beneath the power
module mounting inserts. For additional layout guide-
lines, refer to the FLTR100V10 Filter Module Data
Sheet (FDS01-043EPS).
20
0
LOCAL AMBIENT TEMPERATURE, T
A (°C)
POWER DISSIPATION, PD (W)
10 20 30 40 50 60 70 80 90 100
15
10
5
0
NO HEAT SINK
1/4 IN. HEAT SINK
1/2 IN. HEAT SINK
1 IN. HEAT SINK
PD
TC TS TA
θcs θsa
θsa
T
C TA–()
P
D
-------------------------
θcs–=
