description

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 148

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.

SMFL converters offer the following screening options: Space Prototype

(O), Class H, or Class K. Radiation tolerant to Radiation Hardness

Assurance (RHA) levels of “-” (O) 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.

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.

Isolation between input and output circuits is provided with a transformer

in the forward path and a wide bandwidth magnetic coupling in the feed-

back control loop. The SMFL 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 regulation 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.

The SMFL 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 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 appli-

cation of intermediate voltages to these pins (1.5 to 10.5 volts) should be

avoided.

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.

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.

When paralleled, 76% of the total combined power ratings of the SMFL

converters are available at the load. Overload and short circuit perfor-

mance are not adversely affected during parallel operation.

Features

• 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

• 50 V for up to 120 ms transient protection

• Inhibit input side and output side

• Sync function

• Output trim on single output models

• Indefinite short circuit protection

• Remote sense on single output models

• Parallelable up to 148 watts

MODELS

SINgLE

3.3

5

12

15

DUAL

±5

±12

±15

Crane Aerospace & Electronics Power Solutions

sMFL single and dual dc/dc converters

Crane Aerospace & Electronics

Electronics group (Interpoint Brand)

PO Box 97005 • Redmond WA 98073-9705

425.882.3100 • electronics@craneae.com

www.craneae.com

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Rev H - 20061102

28 VoLt input – 65 Watt