LSO2805S Datasheet, PDF (2/18 Pages) International Rectifier – HYBRID-HIGH RELIABILITY RADIATION HARDENED DC-DC CONVERTER

LSO SERIES
28V Input, Single/Dual Output
Circuit Description
The LSO 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.
An internal EMI filter allows the converter to meet
the conducted emissions requirements of MIL-STD-
461C on the input power leads.
Functional Notes
Input Current Telemetry: The LSO Series single
and dual output models also feature an input current
telemetry with a magnitude of 0 to 3.3V full scale.
The voltage signal at this pin (Pin 7) with respect to
Output Return (Pin 12) is equal to 1.5 times the input
current (Vin TLM (V) =1.5 *Input Current (A)+/-0.1V)
Short Circuit and Overload Protection: Output
current is limited under any load fault condition to
approximately 125% of rated. An overload condition
causes the converter output voltage to drop 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.
Input Undervoltage Lockout (UVLO) and
Undervoltage Release (UVR): The converter is
designed to be protected against an undervoltage
condition. The converter will be in a non-functional
(UVLO) mode when the input voltage is pproximately
15.5V or less. The converter will turn on when the
input voltage rises to 15.5V to 17.9V (defined as
UVR threshold) and will provide a regulated output
as the input voltage reaches 18V.
To take advantage of the latch-up feature, the U/V
Latch Pin (Pin 5) should be shorted (with less than
100 ohms) to the Inhibit Return Pin (Pin 4). Note that
in this mode the converter will latch off if an
undervoltage condition lasts more than 1milli-sec.
The converter is reset by a shorted Enable Input pin
command followed by an open Enable Input pin
command.
Output Overvoltage Protection: The converter
also features an output over-voltage protection.
One OVP circuitry for each output for the dual output
models. In an event the voltage output exceeds a
preset voltage threshold of approximately 120 +/-
5% of nominal voltage output, the converter will
turn off. The input power to the converter or the
signal at the Inhibit pin must be recycled (connecting
and removing the Inhibit pin to/from Inhibit Return
pin) to turn on the converter. This event is possible
only if the converter shuts off due to a false triggering.
The OVP threshold voltage can also be reset to
within 115% to 125% of nominal output voltage
with two external resistors. Refer to the Application
Notes section of the data sheet on page 9.
Inhibit (On/Off Command) : 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 4V with respect to the inhibit return (Pin 4).
Output Voltage Adjustment: The output voltage
of all models can be adjusted greater or less than
the nominal output voltage using a single external
resistor. Refer to the Application Notes section of
the data sheet on page 9.
Should the input voltage drops below 16.5V to 14.5V
(defined as UVLO threshold), the converter will turn
off and remains off so long as the input voltage
remains under the UVLO threshold. The converter
will resume a normal operation when the input line
rises above the UVR threshold. However, the
converter can be configured to remain in a latch-up
mode if desired.
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