F
EATURES
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Fully qualified to Class H or K
–55° to +125°C operation
19 to 40 VDC input
Fully Isolated
Magnetic feedback
Fixed frequency, 600 kHz typical
Topology – Single Ended Forward
Inhibit function – input and output
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 270 watts
DC/DC C
ONVERTERS
28 V
OLT
I
NPUT
SMFLHP SERIES
100 WATT
MODELS
VDC O
UTPUT
SINGLE
3.3
5
12
15
DUAL
±5
±12
±15
Size (max.): 3.005 x 1.505 x 0.400 inches (76.33 x 38.23 x 10.16 mm)
See Figures 16 and 17
Weight:
100 grams maximum
Screening: Space Standard, Class H or Class K (MIL-PRF-38534)
Radiation hardness levels O or R
DESCRIPTION
The SMFLHP Series™ 28 volt DC/DC converters are rated up to
100 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 270 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 67 watts per cubic inch.
I
NHIBIT
The SMFLHP 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. An open
collector TTL compatible low (<0.8 volts) is required between INH1
(pin 4) and Input Common (pin 2) to inhibit the converter. An open
collector TTL compatible low (<0.5 volts) is required between INH2
(pin 12) and Output Common (pin 8) to inhibit the converter. The
application of intermediate voltages to these pins (1.5 to 10.5 volts)
should be avoided.
S
CREENING AND
R
EPORTS
SMFLHP converters offer three screening options (Space Standard,
Class H, or Class K) and two levels of radiation hardness (O and R).
Detailed reports on product performanace are also available.
C
URRENT
S
HARING AND
P
ARALLEL
O
PERATION
Multiple SMFLHP 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 SMFLHP converters. In current
sharing mode, one SMFLHP 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, 90% of the total combined power ratings of the
SMFLHP converters are available at the load. Overload and short
circuit performance are not adversely affected during parallel
operation.
D
ESIGN
F
EATURES
The SMFLHP 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 wide bandwidth magnetic coupling in
the feedback control loop. The SMFLHP Series uses a unique dual
loop feedback technique that controls output current with an inner
feedback loop and 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.
Tight load regulation is achieved through a wide-bandwidth
magnetic feedback circuit. The output voltage on single SMFLHP
models can be easily trimmed by adding an external resistor. (See
Figure 1 for voltage changes with different resistor values.)
®
1
SMFLHP SERIES
100 WATT
ABSOLUTE MAXIMUM RATINGS
Input Voltage
• 19 to 40 VDC
Power Dissipation (Pd)
• 20 watts
Output Power
• 80 to 100 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 IN 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
• 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)
Current –10 to –5 mA
INH1 referenced to input common
Logic low 0.8 V max
INH2 referenced to output common
Logic low 0.5 V 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
• 19 to 40 VDC continuous
• 50 V for 50 msec transient
Case Operating Temperature (Tc)
• –55 to +125°C full power
• –55 to +135°C absolute
Derating Output Power/Current
• Linearly from 100% at 125°C to 0% at 135°C
PINS NOT USED
TR1, Master, and Slave
If not used, leave unconnected
Electrical Characteristics: –55°C to +125°C Tc, 28 VDC Vin, 100% load, free run, 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
NO LOAD TO FULL
INPUT CURRENT
CONDITION
25°C
V
IN
= 19 to 40 VDC
V
IN
= 19 to 40 VDC
Tc = 25°C
Tc = –55°C to +125°C
V
IN
= 19 to 40 VDC
NO LOAD TO FULL
CONTINUOUS
TRANSIENT
1
50 ms
NO LOAD
FULL LOAD
INHIBITED - INH1
INHIBITED - INH2
10 kHz - 10 MHz
Tc = 25°C
POWER DISSIPATION
SHORT CIRCUIT
RECOVERY
50% – 100% – 50%
TRANSIENT
RECOVERY
3
19 – 40 – 19 VDC
TRANSIENT
4
RECOVERY
3
DELAY
OVERSHOOT
SMFLHP283R3S
MIN
3.26
0
0
—
—
—
—
19
—
—
—
—
—
—
70
—
—
—
—
—
—
—
—
TYP MAX
3.3 3.34
—
18
—
10
20
0
0
28
—
70
2.9
9
35
15
72
15
1.5
350
1.5
250
200
3.5
0
60
45
80
50
20
40
50
120
3.1
15
80
50
—
20
4
450
3.0
400
600
10
25
SMFLHP2805S
MIN
4.95
0
0
—
—
—
—
19
—
—
—
—
—
—
77
—
—
—
—
—
—
—
—
TYP MAX
5.00 5.05
—
16
—
15
30
0
0
28
—
70
3.6
9
35
15
80
15
1.5
350
1.5
250
200
3.5
0
80
50
90
50
20
40
50
120
3.73
15
80
50
—
20
4
450
3.0
400
600
10
25
SMFLHP2812S
MIN TYP MAX
11.88 12.00 12.12
0
—
7.5
0
—
—
—
—
19
—
—
—
—
—
—
81
—
—
—
—
—
—
—
—
—
30
45
0
0
28
—
50
3.8
9
35
15
86
15
1.5
450
1.5
250
200
3.5
0
90
85
150
50
20
40
50
80
3.95
15
80
50
—
20
4
700
3.0
400
600
10
50
SMFLHP2815S
MIN TYP MAX
14.8515.00 15.15
0
— 6.67
0
—
—
—
—
19
—
—
—
—
—
—
82
—
—
—
—
—
—
—
—
—
30
45
0
0
28
—
50
4.2
9
35
15
87
15
1.5
450
1.5
250
200
3.5
0
100
95
175
50
20
40
50
80
4.40
15
80
50
—
20
4
700
3.0
400
600
10
50
UNITS
VDC
A
W
mV p-p
mV
mV
VDC
V
mA
A
mA
INPUT RIPPLE
CURRENT
EFFICIENCY
LOAD FAULT
2
Tc = 25°C
STEP LOAD RESP.
mA pp
%
W
ms
mV pk
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 100°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
Microchip MCU
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