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.

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).

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.

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).

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

Features

Parallel operation with current share,

up to 3 units (148 watts)

-55° to +125°C operation

•

16 to 40 VDC input

•

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

•

Indefinite short circuit protection

•

High power density, 87% efficiency

•

MODELS

single

3.3

5

12

15

28

Dual

±5

±12

±15

Other output voltages

available upon request,

including 2 V, 8 V and

54 V single.

Crane Aerospace & Electronics Power Solutions

MFL single and dual dc/dc converters

Crane Aerospace & Electronics

Electronics Group (Interpoint Brand)

POBox97005•RedmondWA98073-9705

425.882.3100•power@crane-eg.com

www.craneae.com/interpoint

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28 VoLt input – 65 Watt

MFL Rev E - 20101026