Operating Features of the PT4850 Triple-Output
The PT4850 series of DC/DC converters provide three
independently regulated logic output voltages, Vo1, Vo2,
and Vo3. Each output is current limited to protect against
load faults. The module will not be damaged by a con-
tinuous load fault applied to any output. Current will
continue to flow into the fault but is reduced as the volt-
age across the fault decreases towards zero.
Applying a load fault above the current limit threshold
to any output causes the affected output to significantly
drop. Also load faults applied to Vo1 will affect Vo2 and
Vo3, once Vo1 drops to within 0.2V of either of these
voltages. However, load faults applied to Vo2 or Vo3 will
not affect the other outputs.
The PT4850 DC/DC converter series have an internal
temperature sensor, which monitors the temperature of
the module’s metal case. If the case temperature exceeds
the specified limit the converter will shut down. The
converter will automatically restart when the sensed
temperature returns to within the normal operating
range. The analog voltage generated by the sensor is
also made available at the ‘TEMP’ output (pin 5), and
can be monitored by the host system for diagnostic pur-
poses. Consult the ‘Pin Descriptions’ section of the data
sheet for more information on this feature.
The PT4850 series of DC/DC converters incorporate
electrical isolation between the input terminals (primary)
and the output terminals (secondary). All converters are
production tested to a withstand voltage of 1500VDC.
The isolation 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 regulation control circuitry for these modules is
located on the secondary (output) side of the isolation
barrier. Control signals are passed between the primary
and secondary sides of the converter via a proprietory
magnetic coupling scheme. This eliminates the use of
opto-couplers. The data sheet ‘Pin Descriptions’ and
‘Pin-Out Information’ provides guidance as to which
reference (primary or secondary) that must be used for
each of the external control signals.
If desired an input fuse may be added to protect against
the application of a reverse input voltage.
The Under-Voltage Lock-Out (UVLO) circuit prevents
operation of the converter whenever the input voltage to
the module is insufficient to maintain output regulation.
The UVLO has approximately 2V of hysterisis. This is
to prevent oscillation with a slowly changing input voltage.
Below the UVLO threshold the module is off and the
enable control inputs, EN1 and EN2 are inoperative.
For technical support and more information, see inside back cover or visit www.ti.com