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PT4682C Datasheet(PDF) 10 Page - Texas Instruments |
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PT4682C Datasheet(HTML) 10 Page - Texas Instruments |
10 / 15 page Application Notes For technical support and more information, see inside back cover or visit www.ti.com PT4660 & PT4680 Series Operating Features & System Considerations for the PT4660/PT4680 Dual-Output DC/DC Converters Over-Current Protection The dual-outputs of the PT4660 and PT4680 series of DC/DC converters have independent output voltage regulation and current limit control. Applying a load current in excess of the current limit threshold at either output will cause the respective output voltage to drop. However, the voltage at Vo2 is derived from Vo1. There- fore a current limit fault on Vo1 will also cause Vo2 to drop. Conversely, a current limit fault applied to Vo2 will only cause Vo2 voltage to drop, and Vo1 will remain in regulation. The current limit circuitry incorporates a limited amount of foldback. The fault current flowing into an absolute short circuit is therefore slightly less than the current limit threshold. Recovery from a current limit fault is automatic and the converter will not be damaged by a continuous short circuit at either output. Output Over-Voltage Protection Each output is monitored for over voltage (OV). For fail safe operation and redundancy, the OV fault detection circuitry uses a separate reference to the voltage regulation circuits. The OV threshold is fixed, and set nominally 25% higher than the set-point output voltage. If either output exceeds the threshold, the converter is shutdown and must be actively reset. The OV protection circuit can be reset by momentarily turning the converter off. This is accomplished by either cycling one of the output enable control pins (EN1 or EN2), or by removing the input power to the converter. Note: If Vo1 or Vo2 is adjusted to a higher voltage, the margin between the respective steady-state output voltage and its OV threshold is reduced. This can make the module sensitive to OV fault detection, that may result from random noise and load transients. Over-Temperature Protection The PT4660/80 DC/DC converters have an internal temperature sensor, which monitors the temperature of the module’s metal case. If the case temperature exceeds a nominal 115°C the converter will shut down. The converter will automatically restart when the sensed temperature returns to about 100°C. 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 purposes. Consult the ‘Pin Descrip- tions’ section of the data sheet for further information on this feature. Under-Voltage Lock-Out 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. Primary-Secondary Isolation The PT4460/80 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. Fuse Recommendations If desired an input fuse may be added to protect against the application of a reverse input voltage. |
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