M3G5003R305T Datasheet, PDF (2/10 Pages) International Rectifier – HYBRID-HIGH RELIABILITY RADIATION HARDENED DC-DC CONVERTER

M3G-SERIES
(50V Input, Triple Output)
Circuit Description
The M3G-Series converters utilize a single-ended
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 with duty factor limiting provides high
line rejection and protection against output over
voltage in the event of an internal control loop failure.
This mechanism limits the maximum output voltage
to approximately 20% over the nominal regardless of
the line voltage.
An internal EMI filter reduces the conducted emissions
to less than 5mA rms on the input power leads. A two
stage output filter reduces the typical output ripple to
less than 20mV peak-to-peak.
An external inhibit port is provided to control converter
operation. The nominal threshold relative to the input
return (pin 2) is 1.4V. If 2.0 volts or greater are applied
to the Inhibit pin (pin 3) then the converter will
operate normally. A voltage of 0.8V or less will cause
the converter to shut-down. The pin may be left
open for normal operation and has a nominal open
circuit voltage of 4.0V.
Synchronization input and output allow multiple
converters to operate at a common switching fre-
quency. Converters can be synchronized to one
another or to an externally provided clock. This can
be used to eliminate beat frequency noise or to avoid
creating noise at certain frequencies for sensitive
systems.
The main (+5 volt) output is regulated by the control
loop and typically exhibits better than 1% regulation.
The auxiliary (±12 volt or ±15 volt) outputs are
maintained through tight coupling in the power
transformer and main output filter inductor and
typically exhibit better than 5% regulation. The main
output and auxiliary outputs are isolated from each
other.
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
36 volts and will shut down when the input voltage
drops below 34 volts. This two volts of hysteresis
reduces the possibility of line noise interfering with
the converter’s start-up and shut down.
Design Methodology
The M3G-Series was developed using a proven
conservative design methodology which includes
selecting radiation tolerant and established reliability
components and fully derating to the requirements
of MIL-STD-975 and MIL-STD-1547 except for the
CDR type ceramic capacitors, a capacitor with 50V
rating is used for in-circuit voltage stress of less than
10V. Careful sizing of decoupling capacitors and
current limiting resistors minimizes the possibility of
photo-current burn-out. Heavy derating of the
radiation hardened power MOSFET virtually
eliminates the possibility of SEGR and SEB. A
magnetic feedback circuit is utilized instead of opto-
couplers to minimize temperature, radiation and
aging sensitivity. PSPICE and RadSPICE were used
extensively to predict and optimize circuit
performance for both beginning and end-of-life.
Thorough design analyses include Radiation
Susceptibility (TREE ), Worst Case, Stress, Thermal,
Failure Modes and Effects (FMEA) and Reliability
(MTBF).
2
www.irf.com