GE Industrial Solutions QW030xx DUAL Series - Manual (Page 12)

Lineage Power
Data Sheet
October 2008
18 Vdc to 36 Vdc or 36 Vdc to 75 Vdc Inputs
QW030xx DUAL Series Power Modules: dc-dc Converters;
Thermal Considerations
(continued)
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. 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
module thermal resistance (
θca) is defined as the max-
imum case temperature rise ( ΔT
C, max
) divided by the
module power dissipation (P
D
):
The location to measure case temperature (T
C
) is
shown in Figure 7. Consult your Lineage Power
Account Manager or Application Engineer for case-to-
ambient thermal resistance vs. airflow for various heat
sink configurations, heights, and orientations. Longitu-
dinal orientation is defined as the long axis of the mod-
ule that is parallel to the airflow direction, whereas in
the transverse orientation, the long axis is perpendicu-
lar to the airflow. These curves are obtained by experi-
mental testing of heat sinks, which are offered in the
product catalog.
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 the case-to-
ambient thermal resistance curves had a thermal-con-
ductive 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 11.
8-1304
Figure 11. QW030-Series 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.
Layout Considerations
Copper paths must not be routed beneath the power
module standoffs. For additional layout guidelines,
refer to the FLTR100V10 or FLTR100V20 data sheet.
θ
ca
ΔTC max ,
P
D
------------------- [ ]
T
C
T
A
– ( )
P
D
------------------------ = =
P D
T C T S T A
θcs θsa
→
θ
sa
TC TA – ( )
PD
--------------------------- θ
cs – =
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