LW025F Ver la hoja de datos (PDF) - Tyco Electronics
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LW025F Datasheet PDF : 16 Pages
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LW025 Single-Output-Series Power Modules:
36 Vdc to 75 Vdc Inputs; 25 W
Advance Data Sheet
March 1999
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(+).
Note that the view in Figure 14 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
Thermal Considerations
Introduction
The LW025 Single-Output-Series Power Modules oper-
ate in a variety of thermal environments; however, suffi-
cient cooling should be provided to help ensure reliable
operation of the unit. Heat-dissipating 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
verified by measuring the case temperature. Peak case
temperature (TC) occurs at the position indicated in Fig-
ure 14.
26.9
(1.06)
TRIM
ON/OFF
-
NC
-
LW025A871
DC-DC CONVERTER
OUT
IN IN:DC 36-75V, 1.20A
+ OUT:DC 5.0V, 5.0A
+
19.6
(0.77)
Increasing airflow 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 airflow rates of
0.3 ms–1 (60 ft./min.) due to other heat-dissipating com-
ponents in the system. Therefore, the natural convec-
tion condition represents airflow 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 airflow necessary for a LW025A
operating at VI = 75 V, an output current of 3.5 A, and a
maximum ambient temperature of 85 °C?
Solution
Given: VI = 75 V, IO = 3.5 A, TA = 85 °C
Determine PD (Figure 18): PD = 4.5 W
Determine airflow (Figure 16): v = 1.0 ms–1
(200 ft./min.)
MADE IN USA
CASE PIN (OPTIONAL)
8-1265(C).c
Note: Dimensions are in millimeters and (inches). Pin locations are
for reference only.
Figure 14. Case Temperature Measurement
Location
10
Tyco Electronics Corp.
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