MFL Single and Dual DC/DC Converters

Crane Aerospace & Electronics Power Solutions

Crane Aerospace & Electronics

Electronics Group (Interpoint Brand)

PO Box 97005 • Redmond WA 98073-9705

425.882.3100 • electronics@craneae.com

www.craneae.com

Page 1 of 13

Rev D - 20060601

28 VOLT INPUT – 65 WATT

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 paralleled 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 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 trans-

former in the forward path and a wide bandwidth magnetic coupling

in the feedback control loop. The MFL uses a unique dual loop feed-

back 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 regula-

tion 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 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.

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 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 synchro-

nizing 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.

• –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 & output side)

• Sync function (in and out)

• 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

28

DUAL

±5

±12

±15

Other output voltages

available upon request,

including 2 V, 8 V and

54 V single.