Crane Aerospace & Electronics Power Solutions
SMFLHP Single and Dual DC/DC Converters
28 VOLT INPUT – 100 WATT
FEATURES
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Fully qualified to Class H or K
–55°C to +125°C operation
19 to 40 VDC input
Fully Isolated
Magnetic feedback
Fixed frequency, 600 kHz typical
Topology – Single Ended Forward
Inhibit function – input and output
Sync function
Output trim on single output models
Indefinite short circuit protection
Remote sense on single output models
Up to 87% efficiency
MODELS
VDC OUTPUT
SINGLE
DUAL
3.3
5
±5
±12
±15
12
15
May be paralleled up to 228 watts
DESCRIPTION
Tight load regulation is achieved through a wide-bandwidth
magnetic feedback circuit. The output voltage on single SMFLHP
models can be easily trimmed up by adding an external resistor.
(See Figure 2 for voltage changes with different resistor values.)
The SMFLHP Series™ 28 volt DC/DC converters are rated up
to 100 watts output power over a –55°C 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 posi-
tive or negative outputs. Current sharing allows the units to be
paralleled for total power of up to 228 watts. The welded, hermet-
ically 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.
INHIBIT
The SMFLHP Series converters have two inhibit terminals
(INH1 and INH2) that can be used to disable power conversion,
resulting in a very low quiescent input current. A low (<0.8 volts)
is required between INH1 (pin 4) and Input Common (pin 2) to
inhibit the converter. A 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.
SCREENING
SMFLHP converters offer screening options to Space Prototype
(O), Class H, or Class K. Radiation tolerant to Radiation
Hardness Assurance (RHA) levels of “-” (O), “P” or “R”, per MIL-
STD-38534. Interpoint model numbers use an “O” in the RHA
designator position to indicate the “-” (dash) Radiation Hardness
Assurance level of MIL-PRF-38534, which is defined as “no
RHA”. See “Class H and K, QML Screening” tables for more
information.
CURRENT SHARING AND PARALLEL OPERATION
Multiple SMFLHP converters may be used in parallel to drive a
common load (see Figure 3). 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) of the master unit. Figure 3 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).
DESIGN FEATURES
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
transformer 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 feedback loop.
When paralleled, 76% 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
operation.
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.
Crane Aerospace & Electronics
Electronics Group (Interpoint Brand)
PO Box 97005 • Redmond WA 98073-9705
Page 1 of 13
Rev H - 20071221
425.882.3100
• electronics@craneae.com
www.craneae.com
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