FEATURES
• Fully qualified to Class H or K
• Radiation hardened
• –55° to +125°C operation
• 16 to 40 VDC input
SMHF SERIES
SINGLE AND DUAL
15 WATT
DC/DC CONVERTERS
28 VOLT NPUT
I
• Fully Isolated
• Red hard optocoupler feedback
• Fixed frequency, 550 kHz typical
• Topology – Single Ended Forward
• Transient protection 50 V/120 ms
• Inhibit function
• Sync function
• Indefinite short circuit protection
• Undervoltage lockout
MODELS
VDC OUTPUT
SINGLE
3.3
5
DUAL
5
12
15
12
15
Size (max.): Non flanged 1.460 x 1.130 x 0.330 (37.08 x 28.70 x 8.38 mm)
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.
• Up to 84% efficiency
Weight:
30 grams maximum.
Screening: Standard, Class H, or Class K (MIL-PRF-38534)
Radiation hardness levels O, L, and R
DESCRIPTION
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 .
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.
INHIBIT FUNCTION
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.
SCREENING AND REPORTS
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.
CONVERTER DESIGN
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.
SYNCHRONIZATION
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.
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.
SHORT CIRCUIT PROTECTION
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.
HIGHER POWER DENSITY
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-
UNDERVOLTAGE LOCKOUT
2
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.
print of 1.7 in , this low profile package offers a total power density
of up to 30 watts per cubic inch.
LOW NOISE, HIGH AUDIO REJECTION
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%
33
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