HTH27022S_15 Datasheet, PDF (9/14 Pages) International Rectifier – HIGH RELIABILITY DC-DC CONVERTER

PRELIMINARY
HTH27022S
Technical Notes
Remote Sensing
Connection of the + Sense and - Sense leads at a remotely located load permits compensation for resistive voltage drop
between the converter output and the load when they are physically separated by a significant distance. This connection
allows regulation at the point of application. To minimize noise pickup that could interfere normal operation of the
converter, a twisted pair for remote sensing is highly recommended. When the remote sensing features is not used, the
sense leads should be connected to their respective output terminals at the converter.
Notes:
(1) If the +Sense connection is unintentionally broken, the converter has a fail-safe output voltage of Vout + 25mV, where
the 25mV is independent of the nominal output voltage.
(2) In the event of both the +Sense and -Sense connections being broken, the output will be limited to Vout + 440mV. This
440mV is also essentially constant independent of the nominal output voltage. While operation in this condition is not
damaging to the device, not all performance parameters will be met.
(3) The +Sense Pin shall be kept from being shorted to the -Sense Pin or the Output Return Pin through a resistance path
<1kΩ, or permanent damages will occur inside the converter.
Inhibiting Converter Output
As an alternative to application and removal of the DC voltage to the input, the user can control the converter output by
providing TTL compatible negative logic (LOW active) signal to Inhibit Pin (Pin 4) with respect to the Input Return Pin (Pin
2). The Inhibit Pin is internally pulled “high” so that when not used, an open connection on the Inhibit Pin permits normal
converter operation. When its use is desired, a logical “low” on this port will shut the converter down.
Synchronization of Multiple Converters
When operating multiple converters, system requirements often may require operation of the converters at a common
frequency. To accommodate this requirement, the converters provide both a synchronization input and output.
The Sync Input port permits synchronization of a HT connverter to any compatible external frequency source operating
between 500 kHz and 600 kHz. This input signal should be referenced to the Input Return and has a 10% to 90% duty
cycle. Compatibility requires transition times less than 100ns, maximum low level of +0.8V and a minimum high level of
+2.0V. The Sync Output of a converter which has been designated as the master oscillator provides a convenient
frequency source for this mode of operation. When external synchronization is not required, the Sync In Pin should be left
unconnected thereby permitting the converter to operate at its own internally set frequency.
The sync output signal is a continuous pulse train factory-set at 520 ± 50 kHz, with a duty cycle of 15 ± 5.0%. This signal
is referenced to the Input Return and has been tailored to be compatible with the Sync Input port. Transition times are less
than 100ns and the low level output impedance is less than 50Ω. This signal is active when the DC input voltage is within
the specified operating range and the converter is not inhibited. This output has adequate drive capability to synchronize
at least five additional converters.
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