F
EATURES
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Fully qualified to Class H or K
Radiation hardened
–55° to +125°C operation
16 to 40 VDC input
Fully Isolated
Red hard optocoupler feedback
MODELS
Fixed frequency, 550 kHz typical
VDC O
UTPUT
Topology – Single Ended Forward
SINGLE
DUAL
Transient protection 50 V/120 ms
3.3
±5
Inhibit function
5
±12
Sync function
12
±15
15
Indefinite short circuit protection
Undervoltage lockout
Size (max.): Non flanged 1.460 x 1.130 x 0.330 (37.08 x 28.70 x 8.38 mm)
Up to 84% efficiency
Flanged 2.005 x 1.130 x 0.330 (50.93 x 28.70 x 8.38 mm)
See Figures 21 through 24 for dimensions.
Weight:
30 grams maximum.
Screening: Standard, Class H, or Class K (MIL-PRF-38534)
Radiation hardness levels O, L, and R
DC/DC C
ONVERTERS
28 V
OLT
I
NPUT
SMHF SERIES
SINGLE AND DUAL
15 WATT
DESCRIPTION
The SMHF Series™ of 28 V DC/DC converters offers a wide input
voltage range of 16 to 40 volts and up to 15 watts of output power.
The units are capable of withstanding short term transients up to 50
volts. The package is a hermetically sealed, seam-welded metal
case. Flanged and non-flanged models are available.
step load transient is as low as 1.3% with a 150 msec recovery time.
Input ripple current is typically 35 mA p-p with output ripple voltage
typically 30 mV p-p .
I
NHIBIT
F
UNCTION
SMHF converters provide an inhibit terminal that can be used to
disable internal switching, resulting in no output and very low quies-
cent input current. The converter is inhibited when a TTL compatible
low (≤0.8 – output disabled) is applied to the inhibit pin. The unit is
enabled when the pin, which is internally connected to a pull-up
resistor, is left unconnected or is connected to an open-collector
gate. The open circuit output voltage associated with the inhibit pin
is 8.5 to 12 VDC. In the inhibit mode, a maximum of 12 mA must be
sunk from the inhibit pin at 28 VDC input.
S
CREENING AND
R
EPORTS
SMHF 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.
C
ONVERTER
D
ESIGN
The SMHF converters are switching regulators that use a quasi-
square wave, single-ended forward converter design with a constant
switching frequency of 550 kHz. Isolation between input and output
circuits is provided with a transformer in the forward path and a
temperature compensated opto-coupler in the feedback control
loop. The opto-coupler is radiation hardened and is especially
selected for space applications.
For the SMHF dual output models, cross regulation is maintained by
tightly coupled output magnetics. Up to 70% of the total output
power is available from either output, providing the opposite output
is simultaneously carrying 30% of the total output power. Predictable
current limit is accomplished by directly monitoring the output load
current and providing a constant current output above the overload
point.
S
YNCHRONIZATION
A synchronization feature is included with the SMHF Series that
allows the user to match the switching frequency of the converter to
the frequency of the system clock. An external synchronization
feature is included that allows the user to adjust the nominally
550kHz operating frequency to any frequency within the range of
500 kHz to 600 kHz. This is initiated by applying a TTL compatible
input of the desired frequency to pin 5.
S
HORT
C
IRCUIT
P
ROTECTION
SMHF Series converters provide short circuit protection by
restricting the output current to approximately 115% of the full load
output current. The output current is sensed in the secondary stage
to provide highly predictable and accurate current limiting, and to
eliminate foldback characteristics.
H
IGHER
P
OWER
D
ENSITY
The SMHF Series offers a new standard of performance for small
size and high power density. At just 0.33 inch high and a total foot-
print of 1.7 in
2
, this low profile package offers a total power density
of up to 30 watts per cubic inch.
U
NDERVOLTAGE
L
OCKOUT
Undervoltage lockout prevents the units from operating below
approximately 14 VDC input voltage to keep system current levels
smooth, especially during initialization or re-start operations.
L
OW
N
OISE
, H
IGH
A
UDIO
R
EJECTION
The SMHF converters’ feed-forward compensation system provides
excellent dynamic response and noise rejection. Audio rejection is
typically 50 dB. Typical output voltage response for a 50% to 100%
1
SMHF SERIES
SINGLE AND DUAL
15 WATT
DC/DC C
ONVERTERS
SYNC AND INHIBIT
Sync In (500 to 600 kHz)
• Duty cycle 40% to 60%
• Logic low 0.8 V max
• Logic high 4.5 V min, 5 V max
• Referenced to input common
• If not used, connect to input common
Inhibit TTL Open Collector
• Logic low (output disabled)
Logic low voltage
≤0.8
V max
Inhibit pin current 4.0 mA max
• Referenced to input common
• Logic high (output enabled)
Open collector or unconnected
ABSOLUTE MAXIMUM RATINGS
Input Voltage
• 16 to 40 VDC
Power Dissipation (Pd)
• 8W
Output Power
• 12 to 15 watts depending on model
Lead Soldering Temperature (10 sec per lead)
• 300°C
Storage Temperature Range (Case)
• –65°C to +150°C
TYPICAL CHARACTERISTICS
Output Voltage Temperature Coefficient
• 100 ppm /°C typical
• 150 ppm/°C maximum
Input to Output Capacitance
• 60 pF typical
Undervoltage Lockout
• 12 V input typical
Current Limit
• 115% of full load typical
Isolation
• 100 megohm minimum at 500 V
Audio Rejection
• 50 dB typical
Conversion Frequency (º55°C to +125°C Tc)
• Free run 550 kHz typical
480 kHz min, 620 kHz max
Inhibit Pin Voltage (unit enabled)
• 8.5 to 12 V
RECOMMENDED OPERATING CONDITIONS
Input Voltage Range
• 16 to 40 VDC continuous
• 0 V for up to 50 msec transient
Case Operating Temperature (Tc)
• –55°C to +125°C full power
• –55°C to +135°C absolute
Derating Output Power/Current (Tc)
• Linearly from 100% at 125°C to 0% at 135°C
Electrical Characteristics: 25°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
LINE REGULATION
LOAD REGULATION
INPUT VOLTAGE
NO LOAD TO FULL
INPUT CURRENT
CONDITION
V
IN
= 16 to 40 VDC
V
IN
= 16 to 40 VDC
10 kHz - 2 MHz
Tc = –55°C to +125°C
Vin = 16 to 40 VDC
NO LOAD TO FULL
CONTINUOUS
TRANSIENT 50 ms
NO LOAD
FULL LOAD
INHIBITED
10 kHz - 10 MHz
Tc = –55°C to +125°C
SHORT CIRCUIT
POWER DISSIPATION
RECOVERY
2
50% – 100% – 50%
TRANSIENT
RECOVERY
2
16 – 40 – 40 VDC
TRANSIENT
3
RECOVERY
2
DELAY
OVERSHOOT
4
SMHF283R3S
MIN
3.27
0
0
—
—
—
—
16
—
—
—
—
—
—
70
—
—
–400
—
–800
—
—
0
TYP MAX
3.30 3.33
—
2.4
—
60
80
5
20
28
—
25
—
5
45
—
73
5
7.5
150
150
550
0.8
10
200
8
160
240
100
50
40
50
65
397
12
80
120
—
8
30
500
300
800
1.2
25
300
SMHF2805S
MIN
4.95
0
0
—
—
—
—
16
—
—
—
—
—
—
73
—
—
–500
—
–800
—
0
0
TYP MAX
5.00 5.05
—
2.4
—
30
150
5
20
28
—
25
560
5
35
—
75
3.5
7.5
150
150
550
0.8
10
100
12
80
240
100
50
40
50
40
624
12
80
120
—
8
30
500
300
800
1.2
25
600
UNITS
VDC
A
W
mV p-p
mV
mV
VDC
V
mA
INPUT RIPPLE
CURRENT
EFFICIENCY
LOAD FAULT
1
mA pp
%
W
ms
mV pk
µs
mV pk
ms
ms
mV pk
STEP LOAD RESP.
STEP LINE RESP.
START-UP
Notes
1. Indefinite short circuit protection not guaranteed above 125°C (case)
2. Recovery time is measured from application of the transient
to the point at which Vout is within regulation.
3. Input step transition time >10µs.
4. Input step transition time <100µs.
2
SMHF SERIES
SINGLE AND DUAL
15 WATT
DUAL OUTPUT MODELS
PARAMETER
OUTPUT VOLTAGE
CONDITIONS
DC/DC C
ONVERTERS
SMHF2805D
MIN
4.95
4.92
—
—
—
—
—
—
—
—
—
16
—
—
—
—
—
—
75
—
—
–600
–600
—
–800
—
—
0
TYP
5.00
5.00
±1.2
—
60
100
5
—
20
—
6
28
—
20
540
6
30
60
77
3
7.5
200
150
150
600
0.8
12
100
MAX
5.05
5.08
1.68
12
160
240
50
100
50
150
7.5
40
50
50
600
12
80
120
—
8
30
600
600
500
800
1.2
30
500
MIN
11.88
11.82
—
—
—
—
—
—
—
—
—
16
—
—
—
—
—
—
74
—
—
–600
–600
—
–750
—
—
0
SMHF2812D
TYP
12.00
12.00
±0.625
—
70
100
5
—
20
—
3
28
—
25
645
5
40
55
81
3
7.5
300
100
200
550
0.8
12
200
MAX
12.12
1218
0.875
15
175
275
50
100
50
150
6
40
50
50
754
12
80
120
—
6
50
600
500
500
750
1.2
25
500
MIN
14.85
14.78
—
—
—
—
—
—
—
—
—
16
—
—
—
—
—
—
74
—
—
–600
–600
—
–750
—
—
0
SMHF2815D
TYP
15.00
15.00
±0.500
—
70
100
5
—
20
—
3
28
—
25
638
5
40
55
82
3
7.5
300
100
200
550
0.8
12
200
MAX
15.15
15.23
0.700
15
175
275
50
100
50
150
6
40
50
50
754
12
80
120
—
6
50
600
600
600
750
1.2
25
500
µs
mV pk
ms
ms
mV pk
%
VDC
V
mA
mV
A
W
mV p-p
mV
UNITS
VDC
Electrical Characteristics: 25°C Tc, 28 VDC Vin, 100% load, free run, unless otherwise specified.
+V
OUT
–V
OUT
V
IN
= 16 to 40 VDC
V
IN
= 16 to 40 VDC
10 kHz - 2 MHz
Tc = –55°C to +125°C
BALANCED +V
OUT
LOAD
–V
OUT
–V
OUT
BALANCED +V
OUT
LOAD
OUTPUT CURRENT
1
OUTPUT POWER
1
OUTPUT RIPPLE
VOLTAGE ±V
OUT
LINE REGULATION
Vin = 16 to 40 VDC
LOAD REGULATION
CROSS REGULATION
2
INPUT VOLTAGE
NO LOAD TO FULL
INPUT CURRENT
NEGATIVE V
OUT
CONTINUOUS
TRANSIENT 50 msec
NO LOAD
FULL LOAD
INHIBITED
10 kHz - 10 MHz
Tc = –55°C to +125°C
SHORT CIRCUIT
3
POWER DISSIPATION
RECOVERY
4
50% – 100% – 50%
+V
OUT
TRANSIENT
–V
OUT
RECOVERY
4
16 – 40 – 40 VDC
TRANSIENT
6
RECOVERY
4
DELAY
OVERSHOOT
7
INPUT RIPPLE
CURRENT
EFFICIENCY
LOAD FAULT
mA p-p
%
W
ms
STEP LOAD RESP.
5
BALANCED LOADS
mV pk
STEP LINE RESP.
± V
OUT
START-UP
Notes
1. Up to 70% of the total output power is available from either output providing
the opposite output is simultaneously carrying 30% of the total output
power. Each output must carry a minimum of 30% of the total output
power in order to maintain regulation on the negative outputs.
2. Effect on –Vout for the following conditions, percentages are of total power:
+Po = 50% to 10% and –Po = 50%
+Po = 50% and –Po = 50% to 10%
3. Indefinite short circuit protection not guaranteed above 125°C (case)
4. Recovery time is measured from application of the transient to point at
which Vout is within regulation.
5. Response of either output with the opposite output held at half of the total
output power.
6. Input step transition time >10µs.
7. Input step transition time <100µs.
4
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