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PT4484C Datasheet(PDF) 5 Page - Texas Instruments |
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PT4484C Datasheet(HTML) 5 Page - Texas Instruments |
5 / 8 page Application Notes For technical support and more information, see inside back cover or visit www.ti.com Operating Features of the PT4470 and PT4480 Series of Isolated DC/DC Converters Under-Voltage Lockout An Under-Voltage Lock-Out (UVLO) inhibits the operation of the converter until the input voltage is above the UVLO threshold (see the applicable data sheet specification). Below this voltage, the module’s output is held off, irrespective of the state of the Inhibit control (pin 3). If the Inhibit control is connected to –Vin (pin 2), the module will automatically power up when the input voltage rises above the UVLO threshold. The UVLO allows the module to produce a clean transition during both power-up and power-down, even when the input voltage is rising or falling slowly. It also reduces the 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 threshold includes about 2V of hysteresis. Once operational, the converter will conform to its operating specifications when the minimum specified input voltage is reached. Over-Current Protection To protect against load faults, the PT4470/80 series of DC/DC converters incorporate an output current limit. Once the load current drawn from the module reaches the current limit threshold, any attempt by the load to draw additional current will result in a significant drop in the module’s regulated output voltage. The current limit circuitry incorporates a limited amount of foldback. This has the effect of slightly reducing the output current from the module when supplying an absolute short circuit. Upon removal of the load fault, the output voltage from the converter will automatically recover to its programmed regulation voltage. Output Over-Voltage Protection The PT4470/80 series of DC/DC converters incorporate circuitry that continually senses the output for an over- voltage (OV) condition. The OV threshold automatically tracks the VID output voltage program setting to a level 25% higher than that programmed at the control pins, VID0 through VID4. If the converter output voltage exceeds the OV 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 is accomplished by either cycling the status of the Inhibit control (pin 3) from “On” to “Off” and then back “On” again, or by momentarily 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 the specified limit (see applicable data sheet), the converter will shut down. The converter will then automatically restart when the sensed temperature drops by about 10°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. Primary-Secondary Isolation Electrical isolation is provided between the input terminals (primary) and the output terminals (secondary). All con- verters are production tested to a primary-secondary withstand voltage of 1500VDC. This specification com- plies with UL60950 and EN60950 and the requirements for operational isolation. Operational isolation allows these converters to be configured for either a positive or negative input voltage source. The data sheet ‘Pin-Out Information’ uses shading to indicate which pins are associated with the primary. They include pins 1 through 5, inclusive. 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 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 PT4470, PT4480 Series |
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