JBW050A1 Datasheet, PDF (12/16 Pages) Lineage Power Corporation – 36 to 75 Vdc Input, 5 Vdc Output; 50 W

JBW050A Power Modules: dc-dc Converter;
36 to 75 Vdc Input, 5 Vdc Output; 50 W
Data Sheet
March 27, 2008
Thermal Considerations (continued)
Heat Transfer With Heat Sinks (continued)
8
7
NO HEAT SINK
6
1/4 in. HEAT SINK
1/2 in. HEAT SINK
5
1 in. HEAT SINK
1 1/2 in. HEAT SINK
4
3
2
1
0
0 0.25 0.51 0.76 1.02 1.27 1.52 1.78 2.03
(50) (100) (150) (200) (250) (300) (350) (400)
AIR VELOCITY, ms^-1 (ft./min.)
8-1052.a
Figure 20. Case-to-Ambient Thermal Resistance
Curves; Either 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 Figure 20 had a
thermal-conductive dry pad between the case and the
heat sink to minimize contact resistance. The use of
Figure 20 is shown in the following example.
Example
If an 85 °C case temperature is desired, what is the
minimum airflow necessary? Assume the JBW050A
module is operating at VI = 54 V and an output current
of 10 A, maximum ambient air temperature of 70 °C,
and the heat sink is 1/2 inch.
Solution
Given: VI = 54 V
IO = 10 A
TA = 70 °C
TC = 85 °C
Heat sink = 1/2 in.
Determine PD by using Figure 18:
PD = 9.5 W
Then solve the following equation:
θca = -T---^C---P--^–--_D---T----^A-
θca = ⁸---⁵---₉--^–-_.-₅--⁷---⁰--
θca = 1.58 ^·°C/W
12
Use Figure 20 to determine air velocity for the 1/2 inch
heat sink.
The minimum airflow necessary for the JBW050A
module is 1.52 m/s (300 ft./min.).
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) shown below (Figure 21).
TC
TS
TA
PD
θcs
θsa
Figure 21. Resistance from Case-to-Sink and
Sink-to-Ambient
8-1304
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:
θsa = ⁽---T----^C-----^–----T----^A----⁾ – θcs
PD
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.
Solder, Cleaning, and Drying
Considerations
Post solder cleaning is usually the final circuit-board
assembly process prior to electrical testing. The result
of inadequate circuit-board cleaning and drying can
affect both the reliability of a power module and the
testability of the finished circuit-board assembly. For
guidance on appropriate soldering, cleaning, and dry-
ing procedures, refer to the Board-Mounted Power
Modules Soldering and Cleaning Application Note
(AP01-056EPS).
EMC Considerations
For assistance with designing for EMC compliance,
please refer to the FLTR100V10 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 data sheet
(FDS01-043EPS).
Lineage Power