Crane Aerospace & Electronics Power Solutions
MFL single and dual dc/dc converters
28 VoLt input – 65 Watt
Features
Parallel operation with current share,
up to 3 units (148 watts)
• -55° to +125°C operation
• 16 to 40 VDC input
VDc O
utPut
single
MODELS
• 50 V for 120 ms transient protection
• Fully isolated, magnetic feedback
• Fixed high frequency switching
• Remote sense or output trim on
single output models
• Inhibit function
• Sync in and Sync Out
3.3
5
12
15
28
Dual
±5
±12
±15
• Indefinite short circuit protection
Other output voltages
available upon request,
including 2 V, 8 V and
54 V single.
• High power density, 87% efficiency
description
The MFL Series™ 28-volt DC/DC converters are rated up to 65
watts of 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 positive
or negative output. Current sharing allows the units to be paral-
leled for total power of up to 148 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 43 watts per cubic
inch. The converters are offered with standard screening, “ES”
screening, or fully compliant to “883” MIL-PRF-38534 Class H
screening. Standard microcircuit drawings (SMD) are available.
i
nhibit
The MFL 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 and no generation of switching
noise. A logic low (<0.8 volts) is required to inhibit the converter
between INH1 (pin 4) and Input Common (pin 2). A logic 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.
s
ync
D
esign
F
eatures
The MFL 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 a wide bandwidth magnetic
coupling in the feedback control loop. The MFL uses a unique
dual loop feedback technique that controls output current with
an inner feedback 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.
The constant frequency, pulse-width modulated converters use a
quasi-square wave single-ended forward design. Tight load regu-
lation is achieved through a wide-bandwidth magnetic feedback
circuit. The output on single MFL models can be trimmed (see
Figure 1 for voltage changes with different resistor values).
Crane Aerospace & Electronics
Electronics Group (Interpoint Brand)
PO Box 97005 • Redmond WA 98073-9705
425.882.3100 • power@crane-eg.com
www.craneae.com/interpoint
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 (see Application Note on
Inhibit and Synchronization).
c
urrent anD
P
arallel
O
PeratiOn
Multiple MFL 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 MFL converters. In current
sharing mode, one MFL 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, 76% of the total combined power ratings of the
MFL converters are available at the load. Overload and short
circuit performance are not adversely affected during parallel
operation
.
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MFL Rev E - 20101026
INTERPOINT [ INTERPOINT CORPORATION COMPANY ]
