M3G2803R312T Datasheet, PDF (2/10 Pages) International Rectifier – HYBRID-HIGH RELIABILITY RADIATION HARDENED DC-DC CONVERTER

M3G2803R312T
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.
The main (+3.3V) output is regulated by the control
loop and typically exhibits better than 1% regulation.
The auxiliary (±12V) 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 power 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
16.5V and will shut down when the input voltage
drops to 15.5V. 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 nominal threshold relative to the input
return (pin 2) is 1.4V. If 2.0V 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
frequency. 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.
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. 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).
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