F
EATURES
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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
DC/DC C
ONVERTERS
28 V
OLT
I
NPUT
SMFL SERIES
65 WATT
MODELS
VDC O
UTPUT
SINGLE
5
12
15
DUAL
±5
±12
±15
Size (max.): 3.005 x 1.505 x 0.400 inches (76.33 x 38.23 x 10.16mm)
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: Standard, Class H, or Class K (MIL-PRF-38534)
Radiation hardness levels O, L and R
DESCRIPTION
I
NHIBIT
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.
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.
S
CREENING AND
R
EPORTS
SMFL converters offer three screening options (Standard, Class H,
or Class K) and three levels of radiation hardness (O, L, and R). See
Tables 1, 2, and 3 for more information. Detailed reports on product
performance are also available and are listed in Table 4.
S
YNC
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.
D
ESIGN
F
EATURES
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.
C
URRENT AND
P
ARALLEL
O
PERATION
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.
1
SMFL SERIES
65 WATT
ABSOLUTE MAXIMUM RATINGS
Input Voltage
• 16 to 40 VDC
Power Dissipation (Pd)
• 14 watts (16 watts SMFL2805S, SMFL2805D)
Output Power
• 50 to 65 watts depending on model
Lead Soldering Temperature (10 sec per lead)
• 300°C
Storage Temperature Range (Case)
• –65°C to +150°C
DC/DC C
ONVERTERS
SYNC AND INHIBIT (INH1, INH2)
Sync In (525 to 675 kHz)
• Duty cycle 40% min, 60% max
• Logic low 0.8 V max
• Logic high 4.5 V min, 9 V max
• Referenced to input common
• If not used, connect to input common
Sync Out
• Referenced to input common
Inhibit (INH1, INH2) TTL Open Collector
• Logic low (output disabled)
INH1 referenced to input common
Logic low 0.8 V max
Inhibit pin current 10 mA max
INH2 referenced to output common
Logic low 0.5 V max
Inhibit pin current 5 mA max
• Logic high (output enabled)
Open collector
TYPICAL CHARACTERISTICS
Output Voltage Temperature Coefficient
• 100 ppm/°C typical
Input to Output Capacitance
• 150 pF, typical
Isolation
• 100 megohm minimum at 500 V
Audio Rejection
• 50 dB typical
Conversion Frequency
• Free run mode 600 kHz typical
550 kHz. min, 650 kHz max
• External sync range 525 to 675 kHz
Inhibit Pin Voltage (unit enabled)
• INH1 = 9 to12 V, INH2 = 6 to 9 V
RECOMMENDED OPERATING CONDITIONS
Input Voltage Range
• 16 to 40 VDC continuous
Case Operating Temperature (Tc)
• –55°C to +125°C full power
PINS NOT USED
TR1, Master, and Slave
If not used, leave unconnected
Electrical Characteristics: 25°C Tc, 28 VDC Vin, 100% load, radiation level O, unless otherwise specified.
SINGLE OUTPUT MODELS
PARAMETER
OUTPUT VOLTAGE
OUTPUT CURRENT
OUTPUT POWER
OUTPUT RIPPLE
VOLTAGE 10 k - 2 MHz
LINE REGULATION
LOAD REGULATION
INPUT VOLTAGE
INPUT CURRENT
CONDITION
Tc = 25°C
V
IN
= 16 TO 40 VDC
V
IN
= 16 TO 40 VDC
Tc = 25°C
Tc = –55°C to +125°C
V
IN
= 16 to 40 VDC
NO LOAD TO FULL
CONTINUOUS
TRANSIENT
1
50 ms
NO LOAD
FULL LOAD
INHIBITED - INH1
INHIBITED - INH2
INPUT RIPPLE
CURRENT
EFFICIENCY
LOAD FAULT
2
10 kHz - 10 MHz
Tc = 25°C
POWER DISSIPATION
SHORT CIRCUIT
Tc = 25°C
RECOVERY
STEP LOAD RESP.
50% – 100% – 50%
TRANSIENT
RECOVERY
3
16 – 40 – 16 VDC
TRANSIENT
4
RECOVERY
3
DELAY
OVERSHOOT
SMFL2805S
MIN
4.95
0
0
—
—
—
—
16
—
—
—
—
—
—
75
TYP MAX
5.00 5.05
—
—
15
30
0
0
28
—
70
—
9
35
15
80
10
50
35
50
20
20
40
50
120
2.5
14
70
50
—
SMFL2812S
MIN TYP MAX
11.88 12.00 12.12
0
0
—
—
—
—
16
—
—
—
—
—
—
81
—
—
30
45
0
0
28
—
50
—
9
35
15
86
5
60
75
100
20
20
40
50
80
2.8
14
70
50
—
SMFL2815S
MIN TYP MAX
14.85 15.00 15.15
0
0
—
—
—
—
16
—
—
—
—
—
—
82
—
—
30
45
0
0
28
—
50
—
9
35
15
87
4.33
65
85
110
20
20
40
50
80
3.0
14
70
50
—
mA pp
%
UNITS
VDC
A
W
mV p-p
mV
mV
VDC
V
mA
A
mA
—
—
—
—
—
—
—
—
12.5
1.5
250
1.5
250
200
3.5
0
16
4
350
3.0
300
300
6
25
—
—
—
—
—
—
—
—
10
1.5
450
1.5
250
200
3.5
0
14
4
700
3.0
400
300
6
50
—
—
—
—
—
—
—
—
10
1.5
500
1.5
250
200
3.5
0
14
4
700
3.0
400
300
6
50
W
ms
mV p
ms
mV pk
µs
ms
mV pk
STEP LINE RESP.
START-UP
Notes
1. Unit will shut down above approximately 45V but will be undamaged and
will restart when voltage drops into normal range.
2. Indefinite short circuit protection not guaranteed above 125°C case.
3. Recovery time is measured from application of the transient to point at
which Vout is within 1% of final value.
4. Transition time
≥
10 µs.
2
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