–55° to +125°C operation
16 to 40 VDC input
Fixed frequency, 550 kHz typical
Topology – Single Ended Forward
50 V for up to 50 ms transient protection
Inhibit and sync functions
Indefinite short circuit protection
Up to 84% efficiency, 28 W/in
SINGLE & DUAL
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)
30 grams maximum.
Screening: Standard, ES, or 883 (Class H).
The MHF+ Series™ of high frequency 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 tran-
sients up to 50 volts. The package is a hermetically sealed, welded
metal case. Flanged and non-flanged models are available.
MHF+ 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 V. In the inhibit mode, a maximum of 4 mA must be sunk
from the inhibit pin.
The MHF+ 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 optical link in the feedback control loop.
For the MHF+ dual output models, good cross regulation is main-
tained by tightly coupled output magnetics. Up to 90% of the total
output power (80% on 2805D) is available from either output,
providing the opposite output is simultaneously carrying 10% of the
total output power (20% on 2805D models). Predictable current limit
is accomplished by directly monitoring the output load current and
providing a constant current output above the overload point.
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 MHF+ 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
this low profile package offers a total power density
of up to 28 watts per cubic inch.
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.
The MHF+ 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%
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 .
Undervoltage lockout prevents the units from operating below
approximately 12 VDC input voltage to keep system current levels
smooth, especially during initialization or re-start operations.
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