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PT4400 Series
Operating Features and System Considerations for
the PT4400 Series of Isolated DC/DC Converters
Over-Current Protection
To protect against load faults, the PT4400 series incor-
porates output over-current protection. Applying a load
that exceeds the converter’s over-current threshold (see
applicable specification) will cause the regulated output
to momentarily fold back and shut down. Following
shutdown the module will periodically attempt to auto-
matically recover by initiating a soft-start power-up. This is
often described as a “hiccup” mode of operation, whereby
the module continues in the cycle of succesive shutdown
and power up until the load fault is removed. Once the fault
is removed, the converter then automatically recovers
and returns to normal operation.
Output Over-Voltage Protection
The PT4400 DC/DC converter series incorporates pro-
tection circuitry that continually senses for an output
overvoltage (OV) condition. The OV threshold auto-
matically tracks the VID output voltage program setting
to a level that is 25% higher than that programmed at
the control pins, VID0 through VID4. If the converter
output voltage exceeds this OV threshold, the converter
is immediately shut down and remains in a latched-off
state. In order to resume normal operation the converter
must be actively reset. This can only be done by momen-
tarily removing the input power to the converter. For
failsafe operation and redundancy, the OV protection
uses circuitry that is independent of the converter’s
internal feedback loop.
Over-Temperature Protection
Over-temperature protection is provided by an internal
temperature sensor, which closely monitors the tempera-
ture of the converter’s metal case. If the case temperature
exceeds a nominal 115°C, the converter will shut down.
The converter will then automatically restart when the
sensed temperature drops back to approximately 105°C.
When operated outside its recommended thermal derating
envelope (see data sheet SOA curves), the converter will
typcially cycle on and off at intervals from a few seconds
to one or two minutes. This is to ensure that the internal
components are not permanently damaged from exces-
sive thermal stress.
Under-Voltage Lockout
The Under-Voltage Lock-Out (UVLO) is designed to
prevent the operation of the converter until the input
voltage is close to the minimum input voltage. The
converter is held off when the input voltage is below the
UVLO threshold, and turns on when the input voltage
rises above the threshold. This prevents high start-up
current during normal power-up of the converter, and
minimizes the current drain from the input source during
low input voltage conditions. The converter will meet
full specifications when the minimum specified input
voltage is reached. The UVLO circuitry also overrides
the operation of the
Remote On/Off
control. Only when
the input voltage is above the UVLO threshold will
the
Remote On/Off
control be functional.
Primary-Secondary Isolation
The PT4400 DC/DC converter series incorporates elec-
trical isolation between the input terminals (primary) and
the output terminals (secondary). All converters are
production tested to a withstand voltage of 1500VDC.
This specification complies with UL60950 and EN60950
and the requirements for operational isolation. This allows
the converter to be configured for either a positive or
negative input voltage source. The data sheet ‘Pin De-
scriptions’ section provides guidance as to the correct
reference that must be used for the external control signals.
Fuse Recommendations
If desired, an input fuse may be added to protect against
the application of a reverse input voltage.
Thermal Considerations
Airflow may be necessary to ensure that the module can
supply the desired load current in environments with
elevated ambient temperatures. The required airflow
rate may be determined from the Safe Operating Area
(SOA) thermal derating chart (see converter specifica-
tions). The recommended direction for airflow is into,
or perpendicular to, the longest side of the module’s
metal case. See Figure 1.
Recommended direction for airflow is
into (perpendicular to) the longest side.
Figure 1
Application Notes