PTEA404120 Datasheet, PDF (6/14 Pages) Texas Instruments – 50-W, 48-V INPUT, 12-V OUTPUT, ISOLATED DC/DC CONVERTER

PTEA404120
SLTS274A – DECEMBER 2006 – REVISED JANUARY 2007
APPLICATION INFORMATION
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Operating Features and System Considerations for the PTEA404120 DC/DC Converter
Overcurrent Protection
To protect against load faults, these converters incorporate output overcurrent protection. Applying a load to the
output that exceeds the converter's overcurrent threshold (see applicable specification) will cause the output
voltage to momentarily fold back, and then shut down. Following shutdown the module will periodically attempt
to automatically 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 successive shutdown and power up until the load fault
is removed. Once the fault is removed, the converter automatically recovers and returns to normal operation.
Output Overvoltage Protection
Each converter incorporates protection circuitry that continually senses for an output overvoltage (OV) condition.
The OV threshold is set approximately 20% higher than the nominal output voltage. If the converter output
voltage exceeds this threshold, the converter is immediately shut down and remains in a latched-off state. To
resume normal operation the converter must be actively reset. This can only be done by momentarily removing
the input power to the converter. For fail-safe operation and redundancy, the OV protection uses circuitry that is
independent of the converter’s internal feedback loop.
Overtemperature Protection
Overtemperature protection is provided by an internal temperature sensor, which closely monitors the
temperature of the converter’s printed circuit board (PCB). If the sensor exceeds a temperature of approximately
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 excessive
thermal stress.
Undervoltage Lockout
The Undervoltage lockout (UVLO) is designed to prevent the operation of the converter until the input voltage is
at the minimum input voltage. 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 UVLO circuitry also
overrides the operation of the Remote On/Off control.
Primary-Secondary Isolation
These converters incorporate electrical isolation between the input terminals (primary) and the output terminals
(secondary). All converters are production tested to a withstand voltage of 2000 VDC. 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 Descriptions section
provides guidance as to the correct reference that must be used for the external control signals.
Input Current Limiting
The converter is not internally fused. For safety and overall system protection, the maximum input current to the
converter must be limited. Active or passive current limiting can be used. Passive current limiting can be a fast
acting fuse. A 125-V fuse, rated no more than 10 A, is recommended. Active current limiting can be
implemented with a current limited Hot-Swap controller.
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 typical characteristics).
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