JFC050C Datasheet, PDF (15/20 Pages) Tyco Electronics – dc-dc Converters; 18 to 36 Vdc Input; 15 Vdc Output; 50 W to 100 W

Data Sheet
October 1999
JFC050C, JFC075C, JFC100C Power Modules:
dc-dc Converters; 18 to 36 Vdc Input, 15 Vdc Output; 50 W to 100 W
Thermal Considerations (continued)
Heat Transfer Without Heat Sinks (continued)
thermal-conductive dry pad between the case and the
heat sink to minimize contact resistance. The use of
Figure 22 is shown in the following example.
18
16
14
12
10
8
VI = 36 V
6
VI = 28 V
VI = 18 V
4
2
0
0
1
2
3
4
5
6
OUTPUT CURRENT, I O (A)
8-1781 (C)
Figure 21. JFC100C Power Dissipation vs. Output
Current at 25 °C
8
7
1 1/2 IN. HEAT SINK
1 IN. HEAT SINK
6
1/2 IN. HEAT SINK
5
1/4 IN. HEAT SINK
NO HEAT SINK
4
3
2
1
0
0
0.5
1.0
1.5
2.0
2.5 3.0
(100) (200) (300) (400) (500) (600)
AIR VELOCITY, IN m/s (ft./min.)
8-1153 (C).a
Figure 22. Case-to-Ambient Thermal Resistance
Curves; Either Orientation
Heat Transfer with Heat Sinks
The power module has 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.).
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):
θca =
∆_----T_----C_---,_--m_----a_--x_-
PD
=
(_---T----C_-----–_----T----A_----)
PD
The location to measure case temperature (TC) is
shown in Figure 18. Case-to-ambient thermal resis-
tance vs. airflow for various heat sink configurations is
shown in Figure 22. These curves were obtained by
experimental 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 Figure 22 had a
Tyco Electronics Corp.
Example
If an 85 °C case temperature is desired, what is the
minimum airflow necessary? Assume the JFC100C
module is operating at VI = 28 V and an output current
of 6.7 A, maximum ambient air temperature of 40 °C,
and heat sink of 1/2 inch.
Solution
Given: VI = 28 V
IO = 6.7 A
TA = 40 °C
TC = 85 °C
Heat sink = 1/2 inch
Determine PD by using Figure 21:
PD = 15.5 W
Then solve the following equation:
θca =
-⁽--T----^C----^–-----T----^A----⁾
PD
θca =
(_{---8---5-----}–_{-----4---0----})
15.5
θca = 2.9 °C/W
Use Figure 22 to determine air velocity for the 1/2 inch
heat sink. The minimum airflow necessary for the
JFC100C module is about 1.15 m/s (230 ft./min.).
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