FEATURES
• –55° to +125°C operation
MHD SERIES
20 WATT
DC/DC CONVERTERS
28 VOLT NPUT
• 16 to 40 VDC input
• Fully Isolated
I
• Magnetic feedback
MODELS
• Fixed frequency
VDC OUTPUT
• Topology – Single Ended Forward
• 50 V for up to 50 ms
transient protection
SINGLE
DUAL
±5
5
• Inhibit and synchronization functions
• Indefinite short circuit protection
12
15
18
±12
±15
3
• Up to 84% efficiency, 21 watts/in
Size (max.): Non-flanged, case H2
2.125 x 1.125 x 0.400 inches (53.98 x 28.58 x 10.16 mm)
Flanged case, K3
2.910 x 1.125 x 0.400 inches (73.91 x 28.58 x 10.16 mm)
See Section B8, cases H2 and K3 for dimensions.
52 grams max., flanged 55 grams max.
Weight:
Screening: Standard, ES, or 883 (Class H). See Section C2 for screening
options, see Section A5 for ordering information.
DESCRIPTION
SYNCHRONIZATION
The MHD offers a synchronization feature that allows the designer
to match the switching frequency of the converter to the frequency
of the system clock. In free-run (unsynchronized) mode, the MHD
unit switches at 625 kHz (nominal). In sync mode, the converter will
run at any frequency between 500 kHz and 675 kHz. The sync
control operates with a quasi-TTL signal at any duty cycle between
40% and 60%.
The MHD Series™ of DC/DC converters offers up to 20 watts of
output power over the full military temperature range with up to 84%
efficiency. Thick-film hybrid techniques provide military/aerospace
reliability levels and optimum miniaturization. The MHD Series
3
power density rating is up to 21 watts/in .
MHD converters are packaged in hermetically sealed metal cases,
making them ideal for use in military, aerospace and other high reli-
ability applications. Units are available with standard screening,
“ES” screening, or fully compliant SMD versions (see Section C2 for
screening conditions).
Synchronizing the converter with the system clock allows the
designer to confine switching noise to clock transitions, minimizing
interference and reducing the need for filtering. The sync pin should
be connected to input common pin when not in use.
CONVERTER DESIGN
WIDE VOLTAGE RANGE
The MHD converters are constant frequency, pulse-width mod-
ulated switching regulators which use a quasi-square wave, single
ended, forward converter design. Tight load regulation (5 mV
typical) is maintained via wide bandwidth magnetic feedback and,
on single output models, through use of remote sense. On dual
output models, the positive output is independently regulated and
the negative output is cross regulated through the use of tightly
coupled magnetics and shunt regulators.
The MHD converters are designed to provide full power operation
over a full 16 to 40 VDC voltage range. Operation below 16 volts,
including MIL-STD-704E emergency power conditions is possible
with derated power. Refer to the low line dropout graph (Figure 15)
for details.
IMPROVED DYNAMIC RESPONSE
The MHD feed-forward compensation system provides excellent
dynamic response and noise rejection. Audio rejection is typically 50
dB. The min. to maximum step line transient response is typically
less than 4%.
Indefinite short circuit protection and overload protection are
provided by a constant current-limit feature. This protective system
senses current in the converter’s secondary stage and limits it to
approximately 115% of the maximum rated output current.
INHIBIT FUNCTION
MHD converters provide an inhibit terminal that can be used to
disable internal switching, resulting in no output and very low
quiescent input current. The converter is inhibited when a TTL
compatible low (≤0.8 V) is applied to the inhibit pin. The unit is
enabled when the pin, which is internally connected to a pull-up
resistor, is left unconnected or is connected to an open-collector
gate. The open circuit output voltage associated with the inhibit pin
is 9 to 11 V. In the inhibit mode, a maximum of 8 mA must be sunk
from the inhibit pin.
MHD converters are provided with internal filtering capacitors that
help reduce the need for external components in normal operation.
For systems that require compliance with MIL-STD-461C’s CE03
standard, Interpoint offers filter/transient suppression modules
(including the FMC-461, FMD-461 and FM-704A series filters) which
will result in compliance. Contact your Interpoint representative for
further details.
B2-47
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