Lineage Power 13
Data Sheet
March 2008 18 Vdc to 36 Vdc Input, 3.3 Vdc Output; 33 W to 66 W
JC050F, JC075F, JC100F Power Modules: dc-dc Converters;
Thermal Considerations (continued)
Heat transfer with Heat Sinks (continued)
8-1153
Figure 27. 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 27 had a
thermal-conductive dry pad between the case and the
heat sink to minimize contact resistance. The use of
Figure 27 is shown in the following example
Example
If an 85 °C case temperature is desired, what is the
minimum airflow necessary? Assume the JC100A
module is operating at nominal line and an output cur-
rent of 20 A, maximum ambient air temperature of
40 °C, and the heat sink is 0.5 in.
Solution
Given: V
I = 28 V
I
O = 20 A
T
A = 40 °C
T
C = 85 °C
Heat sink = 0.5 in.
Determine P
D by using Figure 26:
P
D = 18.2 W
Then solve the following equation:
Use Figure 27 to determine air velocity for the 0.5 inch
heat sink.
The minimum airflow necessary for the JC100F
module is 1.5 m/s (300 ft./min.).
00.5
(100)
1.0
(200)
1.5
(300)
2.0
(400)
2.5
(500)
3.0
(600)
0
1
5
6
7
8
AIR VELOCITY MEASURED IN m/s (ft./min.)
4
3
2
CASE-TO-AMBIENT THERMAL
RESISTANCE, RCA (°C/W)
1 1/2 IN HEAT SINK
1 IN HEAT SINK
1/2 IN HEAT SINK
1/4 IN HEAT SINK
NO HEAT SINK
θca
T
C TA–()
P
D
------------------------
=
θca
85 40–()
18.2
------------------------
=
θca 2.47 °C/W=
