JAW050A and JAW075A Power Modules; dc-dc Converters:
36 Vdc to 75 Vdc Input, 5 Vdc Output; 50 W to 75 W
Data Sheet
April 2008
Custom Heat Sinks
Thermal Considerations (continued)
Heat Transfer with Heat Sinks (continued)
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 25.
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 23 and
24 had a thermal-conductive dry pad between the case
and the heat sink to minimize contact resistance. The
use of Figure 23 is shown in the following example.
TC
TS
TA
PD
θcs
θsa
8-1304(F).e
Figure 25. Resistance from Case-to-Sink and
Sink-to-Ambient
Example
If an 82 °C case temperature is desired, what is the
minimum airflow necessary? Assume the JAW075A
module is operating at VI = 55 V, an output current of
15 A, longitudinal orientation, maximum ambient air
temperature of 40 °C, and the heat sink is 1/4 inch.
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:
(TC – TA)
θsa = ------------------------ – θcs
PD
Solution
Given: VI = 55 V
IO = 15 A
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.
TA = 40 °C
TC = 82 °C
Heat sink = 1/4 inch.
Determine PD by using Figure 20:
PD = 14 W
EMC Considerations
Then solve the following equation:
For assistance with designing for EMC compliance,
refer to the FLTR100V10 Filter Module Data Sheet
(DS99-294EPS).
(TC – TA)
θca = ------------------------
PD
(82 – 40)
-----------------------
θca =
14
Layout Considerations
θca = 3.0 °C/W
Use Figure 23 to determine air velocity for the 1/4 inch
heat sink.
Copper paths must not be routed beneath the power
module standoffs. For additional layout guidelines,
refer to the FLTR100V10 Filter Module Data Sheet
(DS99-294EPS).
The minimum airflow necessary for this module is
1.1 m/s (220 ft./min.).
Lineage Power
13
LINEAGEPOWER [ LINEAGE POWER CORPORATION ]
