Lucent Technologies Inc.
11
Data Sheet
January 2000
36 Vdc to 75 Vdc Inputs; 20 W
LW020 Single-Output-Series Power Modules:
Feature Descriptions (continued)
Synchronization (Optional)
The unit is capable of external synchronization from an
independent time base with a switching rate of
256 kHz. The amplitude of the synchronizing pulse
train is TTL compatible and the duty cycle ranges
between 40% and 60%. Synchronization is referenced
to VI(+).
Thermal Considerations
Introduction
The LW020 Single-Output-Series power module oper-
ates in a variety of thermal environments; however, suf-
cient cooling should be provided to help ensure
reliable operation of the unit. Heat-dissipating compo-
nents inside the unit are thermally coupled to the case.
Heat is removed by conduction, convection, and radia-
tion to the surrounding environment. Proper cooling
can be veried by measuring the case temperature.
Peak case temperature (TC) occurs at the position indi-
8-1265(C)
Note: Dimensions are in millimeters and (inches). Pin locations are
for reference only.
Figure 15. Case Temperature Measurement
Location
Note that the view in Figure
15 is of the metal surface
of the module—the pin locations shown are for refer-
ence. The temperature at this location should not
exceed the maximum case temperature indicated in
the derating curve shown in Figure
16. The output
power of the module should not exceed the rated
power for the module as listed in the Ordering Informa-
tion table.
Heat Transfer
Increasing airow over the module enhances the heat
transfer via convection. Figure
16 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 may be used
typically generate natural convection airow rates of
0.3 ms–1 (60 ft./min.) due to other heat-dissipating
components in the system. Therefore, the natural con-
vection condition represents airow rates of up to
0.3 ms–1 (60 ft./min.). Use of Figure 16 is shown in the following example.
Example
What is the minimum airow necessary for a LW020A
operating at VI = 48 V, an output current of 3.6 A, and a
maximum ambient temperature of 85
°C?
Solution:
Given: VI = 48 V, IO = 3.6 A, TA = 85
°C
Determine PD (Figure 18): PD = 4.5 W Determine airow (Figure 16): v = 1.0 ms–1 (200 ft./min.)
8-1264(C).a
Note: Conversion factor for linear feet per minute to meters per
second: 200 ft./min. = 1 ms–1.
Figure 16. Forced Convection Power Derating;
Either Orientation
19.6
(0.77)
TRIM
–
+
OUT
ON/OFF
NC
+
–
IN LW020A81
DC-DC CONVERTER
MADE IN USA
IN:DC 36-75V, 1.1A
OUT:DC 5.0V, 4A
Lucent
CASE PIN (OPTIONAL)
26.9
(1.06)
TUV Rheinland
40
60
100
0
2
MAX AMBIENT TEMPERATURE, TA (
°C)
POWER
DISSIPATION,
P
D
(W)
50
70
80
90
1
3
4
5
110
120
6
7
3.0 ms –1 (600 ft./min.)
2.0 ms –1 (400 ft./min.)
MAX CASE
TEMPERATURE
NATURAL
CONVECTION
1.0 ms –1 (200 ft./min.)