M3H2803R3S_16 Datasheet, PDF (2/12 Pages) International Rectifier – HYBRID-HIGH RELIABILITY RADIATION HARDENED DC-DC CONVERTER

M3H-SERIES
(+28V Input, Single/Dual Output)
Circuit Description
The M3H-Series converters utilize a single forward topology
with resonant reset. The nominal switching frequency is
500kHz. Electrical isolation and tight output regulation are
achieved through the use of a magnetically coupled feedback.
Voltage feed-forward provides high line rejection.
An internal EMI filter allows the converter to meet the conducted
emissions requirements of MIL-STD-461C on the input
power leads. A two-stage output filter reduces the typical
output ripple to less than 20mV peak-to-peak.
Output current is limited under any load fault condition to
approximately 125% of rated. An overload condition
causes the converter output to behave like a constant
current source with the output voltage dropping below
nominal. The converter will resume normal operation
when the load current is reduced below the current limit
point. This protects the converter from both overload and
short circuit conditions. The current limit point exhibits a
slightly negative temperature coefficient to reduce the
possibility of thermal runaway.
An under-voltage lockout circuit prohibits the converter
from operating when the line voltage is too low to maintain
the output voltage. The converter will not start until the
line voltage rises to approximately 17 volts and will shut
down when the input voltage drops below 16 volts. The
one volt of hysteresis reduces the possibility of line noise
interfering with the converter’s start-up and shut down.
An external inhibit port is provided to control converter
operation. The converter’s operation is inhibited when
this pin is pulled low. It is intended to be driven by an
open collector logic device. The pin may be left open for
normal operation and has a nominal open circuit voltage
of 10.5V with respect to the input return (pin 2).
Single output models feature remote sense to automatically
correct for voltage drops between the converter output anf
the load. The output voltage of dual output models can
be adjusted using a single external resistor.
Design Methodology
The M3H-Series was developed using a proven conservative
design methodology which includes selecting radiation
tolerant and established reliability components and fully
de-rating to the requirements of MIL-STD-975 and
MIL-STD-1547. Heavy de-rating of the power MOSFET
gate and drain voltages minimize the possibility of SEGR
and SEB. A magnetic feedback circuit is utilized instead
of opto-couplers to minimize temperature, radiation and
aging sensitivity. PSPICE was used extensively to predict and
optimize circuit performance for both beginning and
end-of-life. Thorough design analyses include Radiation
Susceptibility (TREE), Stress, Thermal, and Reliability
(MTBF).
2
2016-05-19