S2805S International Rectifier Corp., S2805S Datasheet - Page 2

• Manufacturer Part Number: S2805S
• Description: Hybrid - High Reliability Radiation Hardened Low Power Dc/dc Converter
• Manufacturer: International Rectifier Corp.

Circuit Description
The S-Series converters utilize a single-ended
forward topology with resonant reset. The nominal
switching frequency is 525KHz. 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.
Output power is limited under any load fault condition
to approximately 135% for singles and 145% for
duals 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. There are no
latching elements included in the load fault protection
circuits to eliminate the possibility of falsely triggering
the protection circuits during single event radiation
exposure.
An under-voltage protection circuit prohibits the
converter from operating when the line voltage is
too low for safe operation. The converter will not
start until the line voltage rises to approximately 12V.
S-SERIES
2
Design Methodology
The S-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.
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 was 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
and Reliability (MTBF).
An external enable port is provided to control
converter operation. This input is intended for
operation with an open collector transistor drive or
a relay closure to the input return. The pin may be
left open for normal operation and has a nominal
open circuit voltage of 10.5V.
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