mfw SerieS
70 watt
DC/DC Converters
28 volt Input
NOT RECOMMENDED FOR NEW DESIGNS
Features
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–55°C to + 85°C operation
19 to 40 VꢁC input
MꢀꢁELS
VDC Output
Fully Isolated
single
Dual
±12
±15
tRiple
+5 & ±12
+5 & ±15
ꢀptocoupler feedback
Fixed frequency, 245 kHz typical
Topology – Push-Pull Forward
5
12
15
50 V for up to 50 ms transient protection
Inhibit/sync function
Size (max.): 3.20 x 2.46 x 0.595 inches (81.3 x 62.5 x 15.11 mm)
See case L for dimensions.
Indefinite short circuit protection
Remote sense on single models
Up to 84% efficiency
Weight:
140 grams typical
Screening: Standard or ES. See “85°C Non-QML Products–Environmental
Screening (Standard & ES)“ screening table for more information.
description
The MFW Series™ of ꢁC/ꢁC converters offers up to 70 watts of
power from single, dual, or triple outputs in one package. Using hybrid
thick film technology a power density of over 20 watts per cubic inch
is achieved. These devices are packaged in hermetically sealed cold
rolled steel enclosures with a tin plate finish making them ideal for use
in military, aerospace, or other high reliability applications. Unscreened
models are guaranteed to pass a gross leak test (maximum leak rate
of 0.001 atm-cc/sec). Environmentally screened units (designated
by the /ES suffix) are hermetically solder sealed. See Section C2 for
screening specifications.
wiDe VOltage Range
All models of the MFW Series are designed to provide full power
operation over an input voltage range of 19 to 40 VꢁC. ꢀperation
below an input of 19 volts, including operation in MIL-STꢁ-704E emer-
gency power conditions, is possible with derated output power. Please
refer to the derating information and the low voltage drop-out graphs
(Figures 10 and 11) on the following pages.
wiDe teMpeRatuRe Range
Full load operation of any of the MFW Series converters is available
at case temperatures of –55°C to + 85°C. ꢀperation up to +125°C is
possible with derated output power. The MFW Series converters are
provided in a flange mount case designed to facilitate the removal of
internally generated heat. Because of this, heat sinking requirements
are minimal. Sustained full power operation does however require that
an efficient heat sink be attached to the baseplate. Please refer to the
heat sink requirements section for more information.
Design MethODOlOgy
The MFW Series converters utilize a quasi-square wave forward
converter design with a nominal switching frequency of 245 kHz.
Isolation between input and output is provided with a transformer in the
forward power loop and a wideband, temperature insensitive optical
link in the feedback control loop. ꢀutput regulation is accomplished
with constant frequency pulse width modulation. In addition, the load
regulation of the single output models is further enhanced through
the use of remote output voltage sense pins to overcome the adverse
effects of line resistance voltage drops. Short circuit protection is
provided by detecting peak primary switching current on a cycle by
cycle basis and limiting it to approximately 130% of the full load input
current. This method results in quick and positive current limiting under
short circuit conditions.
inhibit/synC FeatuRe
Standard on all models of the MFW Series is a dual mode inhibit/sync
pin. This pin serves as both an output inhibit and as a synchronization
input. In the inhibit mode an open collector TTL compatible low (<0.8
V) will disable internal switching thereby inhibiting the unit’s output.
Inhibiting in this manner results in an extremely low quiescent current.
Since a pull-up resistor is included internally, this pin may be left open
should the inhibit function not be desired.
lOw nOise
The MFW Series converters offer low noise on both the input and
output lines. A two section, four pole LC input filter is included to
provide very low reflected line ripple current. Adherence to MIL-STꢁ-
461C (CE03) is possible with the addition of the FMB-461 filter. ꢀutput
ripple is maintained at less than 50 mV p-p for single and dual output
models and 85 mV for triple output models.
In a digital system it is often desirable to synchronize the input or
output ripple with the system clock. For this reason each model of the
MFW Series was designed to synchronize with a system clock applied
to the inhibit/sync pin. Please refer to the technical data section for
timing details for the external sync feature.
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