Fully qualified to Class H or K
–55° to +125°C operation
16 to 40 VDC input
Fixed frequency, 550 kHz typical
Topology – Single Ended Flyback
Indefinite short circuit protection
5 watts output power
Up to 76% efficiency
Size (max.): 1.075 x 1.075 x 0.270 inches
(27.31 x 27.31 x 6.86 mm)
See Figures 23 and 24 for dimensions.
15 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
The SMSA Series™ of high frequency DC/DC converters offers a
new standard of performance for low power, space qualified DC/DC
converters. SMSA converters provide up to 5 watts output power
over the full military temperature range of –55°C to +125°C with up
to 76% efficiency. Thick-film hybrid techniques provide military/aero-
space reliability levels and optimum miniaturization. The hermeti-
cally sealed case is only 1.075 by 1.075 inches — with a height of
only 0.270 inches. Power density for the SMSA Series converters is
16 watts per cubic inch. The SMSA Series’ small size, light weight,
and hermetically sealed metal packages make them ideal for use in
space, military, aerospace and other high reliability applications.
The SMSA converters are designed to provide full power operation
over the full 16 to 40 VDC voltage range. An undervoltage lockout
feature keeps the converter shutdown below approximately 13 VDC
to ensure smooth initialization.
The SMSA feed-forward compensation system provides excellent
dynamic response and noise rejection. Audio rejection is typically 50
dB. The minimum to maximum step line transient response is typi-
cally less than 1%.
SMSA converters offer three screening options – Space prototype
Class H, or Class K – and two levels of radiation hardness. See
Tables 1 through 3 for more information. Detailed reports on product
performance are also available and are listed in Table 4.
SMSA converters provide a TTL open collector-compatible inhibit
feature that can be used to disable internal switching and inhibit the
unit’s output. Inhibiting in this manner results in low standby current,
and no generation of switching noise.
The converter is inhibited when the TTL compatible low (≤0.8V) 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 9 to 11 VDC. In the inhibit mode, a
maximum of 4 mA must be sunk from the inhibit pin at 28 VDC input.
The SMSA converters are switching regulators that use a flyback
converter design with a constant switching frequency of 550 kHz.
They are regulated, isolated units using a pulse width modulated
topology and built as high reliability thick-film hybrids. Isolation
between input and output circuits is provided with a transformer in
the forward power loop and an optical link in the feedback control
loop. Excellent input line transient response and audio rejection is
achieved by an advanced feed-forward compensation technique.
Negative output regulation is maintained by tightly coupled
magnetics. Predictable current limit is accomplished by direct moni-
toring of the output load current, which results in a constant current
output above the overload point. Internal input and output filters
eliminate the need for external capacitors.
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