FEATURES
SMFL SERIES
65 WATT
DC/DC CONVERTERS
28 VOLT INPUT
• Fully qualified to Class H or K
• –55° to +125°C operation
• 16 to 40 VDC input
• Fully Isolated
• Magnetic feedback
• Fixed frequency, 600 kHz typical
• Topology – Single Ended Forward
• Inhibit input side and output side
• 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
3.3
5
DUAL
5
12
15
12
15
• Parallelable up to 180 watts
Size (max.): 3.005 x 1.505 x 0.410 inches (76.33 x 38.23 x 10.41 mm)
See Figures 17 and 18 for dimensions. Case options V, W, Y, and
Z are available by special order. Please refer to our databook or
contact your Interpoint representative for more information.
Weight:
85 grams maximum
Screening: Space prototype, Class H, or Class K (MIL-PRF-38534)
Radiation hardness levels O or R
Available configurations: OO, HO, HR, KR
DESCRIPTION
INHIBIT
The SMFL Series™ 28-volt DC/DC converters are rated up to 65
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 180 watts. The welded, hermetically sealed package
is only 3.0 x 1.5 x 0.40 inches, giving the series an overall power
density of up to 45 watts per cubic inch.
The SMFL Series converters have two TTL compatible inhibit termi-
nals (INH1 and INH2) that can be used to disable power conversion,
resulting in a very low quiescent input current and no generation of
switching noise. An open collector TTL compatible low (<0.8 volts)
is required to inhibit the converter between INH1 (pin 4) and Input
Common (pin 2). An open collector TTL compatible low (<0.5 volts)
is required to inhibit the converter between INH2 (pin 12) and Output
Common (pin 8). The application of intermediate voltages to these
pins (1.5 to 10.5 volts) should be avoided.
SCREENING AND REPORTS
SMFL converters offer three screening options (Space prototype,
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.
SYNC
Converters may be synced to an external clock (525 to 675 kHz) or
to one another by using the sync in or out pins. The nominal free-
run switching frequency is 600 kHz.
DESIGN FEATURES
CURRENT AND PARALLEL OPERATION
The SMFL Series converters are switching regulators that use a
quasi-square wave, single ended forward converter design with a
constant switching frequency of 600 kHz typical.
Multiple single output SMFL converters may be used in parallel to
drive a common load. In this mode of operation the load current is
shared by two or three SMFL converters. In current sharing mode,
one SMFL 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). Note that synchronizing
the units together 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). See Figure 2 for a block diagram of
parallel connections.
Isolation between input and output circuits is provided with a trans-
former in the forward path and a wide bandwidth magnetic coupling
in the feedback control loop. The SMFL uses a unique dual loop
feedback technique that controls output current with an inner feed-
back loop and an output voltage with a cascaded voltage mode
feedback loop.
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, but without the cost and
complexity.
When paralleled, 95% of the total combined power ratings of the
SMFL converters are available at the load. Overload and short
circuit performance are not adversely affected during parallel
operation.
The constant frequency, pulse-width modulated converters use a
quasi-square wave single-ended forward design. Tight load regula-
tion is achieved through a wide-bandwidth magnetic feedback
circuit. The output voltage on single SMFL models can be trimmed
to a specific output voltage by adding an external resistor.
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