1

SMFL SERIES

65 WATT

MODELS

SINGLE

3.3

5

12

15

DUAL

±5

±12

±15

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

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.

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.

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.

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.

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.

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.

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, 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.

• 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

• Parallelable up to 180 watts