Fully qualified to Class H or K
–55° to +125°C operation
16 to 40 VDC input
Fixed frequency, 600 kHz typical
Topology – Single Ended Forward
Indefinite short circuit protection
Up to 30 watts output power
Trim function on single
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 (73.79 x 28.58 x 10.16 mm)
• Up to 81% efficiency
See Figures 22 through 25 for dimensions.
Non-flanged 52 grams max., flanged 55 grams max.
Screening: Space prototype, Class H, or Class K (MIL-PRF-38534)
Radiation hardness levels O or R
The SMTR Series™ of 28 volt DC/DC converters offers up to
30 watts of output power from single or dual output configurations.
The operate over the full military temperature range of –55°C to
+125°C with up to 84% efficiency. SMTR converters are packaged
in hermetically sealed metal enclosures, making them ideal for use
in military, aerospace and other high reliability applications.
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. 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 sync pin should be connected to input
common pin when not in use.
SMTR converters offer three screening options (Standard, Class H,
or Class K) and two levels of radiation hardness (O or R). See
Tables 1, 2, and 3 for more information. Detailed reports on product
performance are also available and are listed in Table 4.
SMTR converters are designed to provide full power operation over
a full 16 to 40 Vdc voltage range. Operation below 16 volts,
including MIL-STD-704D emergency power conditions is possible
with derated power.
The SMTR converters are constant frequency, pulse-width mod-
ulated switching regulators which use a quasi-square wave, single
ended, forward converter design. Tight load regulation is maintained
by using a 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.
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.
SMTR 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. For the lowest noise performance, connec-
tion of the case to input common is recommended. The connection
can be hard-wired or AC coupled with a small ceramic bypass
The SMTR Series feed-forward compensation system provides
excellent dynamic response and noise rejection. Audio rejection is
typically 50 dB. The min. to max. step line transient response is typi-
cally less than 4%.
SMTR 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 (≤0.8V) 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 Vdc. In the inhibit mode, a maximum of 8 mA must be sunk
from the inhibit pin.
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