Crane Aerospace & Electronics Power Solutions
MHF+ Single, Dual and Triple DC/DC Converters
28 VOLT INPUT – 15 WATT
SYNCHRONIZATION
SOFT START FEATURE
A synchronization feature is included with the MHF+ 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 550
kHz 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.
The soft-start feature provides a controlled 20 milliseconds turn-on
to minimize inrush current and reduce overshoot at initial start-up or
when inhibit is released.
SYNCHRONIZATION
To synchronize the converter’s switching frequency to a system
clock apply the clock signal to the sync terminal (pin 7). When
multiple converters are powered from a single power source, asyn-
chronous (free run) operation will result in lower peak noise for
common spectral peaks, but synchronous operation will eliminate
any possibility of interference frequencies in the low audio band.
Source impedance of the signal should be less than 100 ohms and
the transition time should be less than 100 nanoseconds. The
capacitively coupled sync input will synchronize on a differential
signal of as low as 4 volts to as high as 5 V. If the sync function is
not used, the terminal should be left open.
SHORT CIRCUIT PROTECTION
MHF+ 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.
UNDERVOLTAGE LOCKOUT
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.
SHORT CIRCUIT PROTECTION
Internal current limiting circuitry protects all three outputs against
short circuits. When output power exceeds approximately 130% of
maximum output power, the output currents are limited. In addition,
separate current limiting circuitry protects each output individually
resulting in normal operation of either the main or the auxiliaries,
whichever is not in a shorted condition.
MHF+ SERIES™ TRIPLE DC/DC CONVERTERS
MHF+ Series™ Triple DC/DC converters provide a wide input
voltage range of 16 to 48 VDC delivering 15 watts of total output
power with output voltages of +5 and 12 or +5 and 15 VDC. The
main output, +5 VDC, will supply up to 7.5 watts and the auxiliaries
will supply up to 7.5 watts of combined power. Full power operation
at -55° C to +125° C plus the ability to withstand transients of up to
80 V for up to 120 milliseconds make these converters an ideal
choice for your high reliability systems.
PACKAGING
MHF+ Triple converters are packaged in hermetically sealed metal
cases. MHF+ Triple converters can be purchased in a flanged or
non-flanged case. The flanged option provides increased heat dissi-
pation and also provides greater stability when mechanically
secured.
CONVERTER DESIGN
MHF+ Triple Series of DC/DC converters incorporate dual-phase,
phase-shifted technology with a continuous flyback topology. This
design eliminates a minimum load requirement on the main output
and eliminates cross regulation effects between the main output
voltage and the auxiliary output voltages. The phase-shifted design
offers a further benefit in reduced input and output ripple.
INHIBIT FUNCTION
An open collector, TTL compatible, inhibit terminal (pin 1) provides
shut-down and start-up control. Applying a logic level low (<0.8 V),
referenced to input common, will disable the output of the converter.
When inhibited input current is reduced to 5 mA or less and there is
no generation of switching noise. The inhibit terminal typically sinks
3 mA when the converter is inhibited.
Leaving the terminal open or pulling it high will enable the converter.
Use an open collector interface for logic high voltages of up to 11
volts. (Refer to Figure 2 for a connection diagram.) An open collector
interface is not required if the logic high is in excess of the open
circuit voltage of the inhibit terminal, 11 volts, but less than 40 volts.
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