JBW050F Power Modules: dc-dc Converter;
36 to 75 Vdc Input, 3.3 Vdc Output; 33 W
Data Sheet
September 20, 2004
Thermal Considerations (continued)
12
10
8
Heat Transfer with Heat Sinks (continued)
8
6
MAX CASE TEMP
3.0 m/s (600 ft./min.)
2.0 m/s (400 ft./min.)
1.0 m/s (200 ft./min.)
0.5 m/s (100 ft./min.)
0.25 m/s (50 ft./min.)
7
NO HEAT SINK
1/4 in. HEAT SINK
1/2 in. HEAT SINK
1 in. HEAT SINK
4
2
0
6
5
1 1/2 in. HEAT SINK
NATURAL CONVECTION
4
0
20
40
60
80
100
120
LOCAL AMBIENT TEMPERATURE, TA (˚C)
3
2
1-0705
Figure 19. Forced Convection Power Derating with
No Heat Sink; Either Orientation
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)
Heat Transfer with Heat Sinks
AIR VELOCITY, ms-1 (ft./min.)
8-1052.a
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.-lb.).
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.
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 (∆TC, max) divided by the
module power dissipation (PD):
Example
If an 85 °C case temperature is desired, what is the
minimum airflow necessary? Assume the JBW050F
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.
(TC – TA)
∆TC, max
--------------------
------------------------
=
θca =
PD
PD
The location to measure case temperature (TC) is
shown in Figure 17. Case-to-ambient thermal resis-
tance vs. airflow is shown, for various heat sink config-
urations and heights, in Figure 20. These curves were
obtained by experimental testing of heat sinks, which
are offered in the product catalog.
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 = 7.7 W
Then solve the following equation:
T
C – TA
-------------------
PD
θca =
θca =
85 – 70
-----------------
7.7
θca = 1.95 °C/W
12
Tyco Electronics Power Systems
LINEAGEPOWER [ LINEAGE POWER CORPORATION ]
