
12
Lucent Technologies Inc.
Data Sheet
December 1999
18 Vdc to 36 Vdc or 36 Vdc to 75 Vdc Inputs, 5 W
LC/LW005-Series Power Modules:
Thermal Considerations
Sufcient cooling should be provided to help ensure
reliable operation of the power module. Heat-dissipat-
ing components inside the unit are thermally coupled to
the case. Heat is removed by conduction, convection,
and radiation to the surrounding environment. Proper
cooling can be veried by measuring the case temper-
ature. The case temperature (TC) should be measured
at the position indicated in Figure
21.8-1363(C).a
Note: Dimensions are in millimeters and (inches). Pin locations are
for reference only.
Figure 21. Case Temperature Measurement
Location
Note that the view in Figure
21 is of the surface of the
module—the pin locations shown are for reference. The
temperature at this location should not exceed a maxi-
mum case temperature of 105
°C. The output power of
the module should not exceed the rated power for the
module as listed in the Ordering Information table.
The LC/LW005-Series Power Modules operate at
IO = IO, max in an 85
°C ambient temperature with
0.25 ms–1 (50 ft./min.) airow. This airow is present in
a typical circuit pack environment in a natural cooled
equipment rack, with other components causing airow
through the chimney effect. In very low airow environ-
ments, such as small enclosures, the module should
be derated approximately 10
°C at full load. Note that
these are approximations and that actual case temper-
ature measurements in the equipment rack should be
taken to verify the case temperature does not exceed
105
°C.
Heat Transfer Characteristics
Increasing airow over the module enhances the heat
transfer via convection. Figure
22 shows the maximum
power that can be dissipated by the module without
exceeding the maximum case temperature versus local
ambient temperature (TA) for natural convection
through 3.0 ms–1 (600 ft./min.).
Systems in which these power modules are used typi-
cally generate natural convection airow rates of
0.25 ms–1 (50 ft./min.) due to other heat dissipating
components in the system. Therefore, the natural con-
vection condition represents airow rates of approxi-
mately 0.25 ms–1 (50 ft./min.). Use of Figure 22 is shown in the following example.
Example
What is the minimum airow necessary for an LW005A
operating at 75 V, an output current of 1 A, and a maxi-
mum ambient temperature of 90
°C?
Solution:
Given: VI = 75 V, IO = 1 A (IO, max), TA = 90
°C
Determine PD (Figure 27): PD = 1.75 W Determine airow (Figure 22): v = 1.0 ms–1 (200 ft./min.)
8-2623(C)
Figure 22. LC/LW005-Series Forced Convection
Power Derating
dc-dc POWER MODULE
16.0 (0.63)
+
–
+
–
OUT
IN
10.0
(0.40)
85
90
95
100
105
110
0.0
2.5
1.5
1.0
2.0
80
3.0
0.5
MAX AMBIENT TEMPERATURE, TA ( C)
POWER
DISSIPATION,
P
D
(W)
NATURAL CONVECTION
3.0 ms –1 (600 ft./min.)
2.0 ms –1 (400 ft./min.)
1.5 ms –1 (300 ft./min.)
1.0 ms –1 (200 ft./min.)
MAX CASE
TEMPERATURE