Fully qualified to Class H or K
–55° to +125°C operation
19 to 40 VDC input
Fixed frequency, 600 kHz typical
Topology – Single Ended Forward
Inhibit function – input and output
Output trim on single output models
Indefinite short circuit protection
Remote sense on single output models
Up to 87% efficiency
Parallelable up to 270 watts
Size (max.): 3.005 x 1.505 x 0.400 inches (76.33 x 38.23 x 10.16 mm)
See cases “U maximum dimensions” and “U” for dimensions.
86 grams maximum
Screening: Space Prototype, Class H, or Class K
Radiation hardness levels O or R
See “QA Screening: Class H and K, QML” for more information.
Available configurations: OO, HO, HR, KR
The SMFLHP Series™ 28 volt DC/DC converters are rated up to
100 watts output power over a –55° to +125°C temperature range
with a 28 Vdc nominal input. On dual output models, up to 70% of
the rated output power can be drawn from either the positive or
negative outputs. Current sharing allows the units to be paralleled
for total power of up to 270 watts. The welded, hermetically sealed
package is only 3.005 x 1.505 x 0.400 inches, giving the series an
overall power density of up to 67 watts per cubic inch.
The SMFLHP Series converters have two TTL compatible inhibit
terminals (INH1 and INH2) that can be used to disable power
conversion, resulting in a very low quiescent input current. An open
collector TTL compatible low (<0.8 volts) is required between INH1
(pin 4) and Input Common (pin 2) to inhibit the converter. An open
collector TTL compatible low (<0.5 volts) is required between INH2
(pin 12) and Output Common (pin 8) to inhibit the converter. The
application of intermediate voltages to these pins (1.5 to 10.5 volts)
should be avoided.
SMFLHP converters offer screening options to Space Prototype (O),
Class H, or Class K. Available radiation hardness (RHA) levels are
O or R. See “QA Screening: Class H and K, QML” for more infor-
Multiple SMFLHP converters may be used in parallel to drive a
common load (see Figure 2). In this mode of operation the load
current is shared by two or three SMFLHP converters. In current
sharing mode, one SMFLHP converter is designated as a master.
The SLAVE pin (pin 11) of the master is left unconnected and the
MSTR/INH2 pin (pin 12) of the master is connected to the SLAVE
pin (pin 11) of the slave units. The units designated as slaves have
the MSTR/INH2 pin (pin 12) connected to the SNS RTN pin (pin 9).
Figure 2 shows the typical setup for two or three units in parallel.
Note that synchronizing the units together (though shown in the
figure) is not required for current sharing operation. A second slave
unit may be placed in parallel with a master and slave; this requires
the TRI pin (pin 3) of the master unit to be connected to the SNS
RTN pin (pin 9).
When paralleled, 90% of the total combined power ratings of the
SMFLHP converters are available at the load. Overload and short
circuit performance are not adversely affected during parallel
The SMFLHP Series converters are switching regulators that use a
quasi-square wave, single ended forward converter design with a
constant switching frequency of 600 kHz.
Isolation between input and output circuits is provided with a trans-
former in the forward path and wide bandwidth magnetic coupling in
the feedback control loop. The SMFLHP Series uses a unique dual
loop feedback technique that controls output current with an inner
feedback loop and output voltage with a cascaded voltage mode
The additional secondary current mode feedback loop improves
transient response in a manner similar to primary current mode
control and allows for ease of paralleling.
Tight load regulation is achieved through a wide-bandwidth
magnetic feedback circuit. The output voltage on single SMFLHP
models can be easily trimmed by adding an external resistor. (See
Figure 1 for voltage changes with different resistor values.)
Interpoint, a Crane Co. Company
PO Box 97005 • Redmond WA 98073-9705
425-895-4053 • email@example.com
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