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LNK405EG Datasheet(PDF) 4 Page - Power Integrations, Inc. |
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LNK405EG Datasheet(HTML) 4 Page - Power Integrations, Inc. |
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4 / 20 page  Rev. D 08/11 4 LNK403-409/413-419 www.powerint.com Figure 6. Remote ON/OFF VOLTAGE MONITOR pin Control 5.9 V Regulator/Shunt Voltage Clamp The internal 5.9 V regulator charges the bypass capacitor connected to the BYPASS pin to 5.9 V by drawing a current from the voltage on the DRAIN pin whenever the power FET is off. The BYPASS pin is the internal supply voltage node. When the power FET is on, the device operates from the energy stored in the bypass capacitor. Extremely low power consumption of the internal circuitry allows LinkSwitch-PH to operate continuously from current it takes from the DRAIN pin. A bypass capacitor value of 10 or 100 mF is sufficient for both high frequency decoupling and energy storage. In addition, there is a 6.4 V shunt regulator clamping the BYPASS pin at 6.4 V when current is provided to the BYPASS pin through an external resistor. This facilitates powering of LinkSwitch-PH externally through a bias winding to increase operating efficiency. It is recommended that the BYPASS pin is supplied current from the bias winding for normal operation. Auto-Restart In the event of an open-loop fault (open FEEDBACK pin resistor or broken path to feedback winding), output short-circuits or an overload condition the controller enters into the auto-restart mode. The controller annunciates both short-circuit and open-loop conditions once the FEEDBACK pin current falls below the I FB(AR) threshold after the soft-start period. To minimize the power dissipation under this fault condition the shutdown/auto-restart circuit turns the power supply on (same as the soft-start period) and off at an auto-restart duty cycle of typically DC AR for as long as the fault condition persists. If the fault is removed during the auto-restart off-time, the power supply will remain in auto-restart until the full off-time count is completed. Special consideration must be made to appropriately size the output capacitor to ensure that after the soft-start period (t SOFT) the FEEDBACK pin current is above the IFB(AR) threshold to ensure successful power-supply start-up. After the soft-start time period, auto-restart is activated only when the FEEDBACK pin current falls below I FB(AR). Over-Current Protection The current limit circuit senses the current in the power FET. When this current exceeds the internal threshold (I LIMIT), the power FET is turned off for the remainder of that cycle. A leading edge blanking circuit inhibits the current limit comparator for a short time (t LEB) after the power FET is turned on. This leading edge blanking time has been set so that current spikes caused by capacitance and rectifier reverse recovery will not cause premature termination of the power FET conduction. Line Under/Overvoltage Protection This device includes both line under- and overvoltage detection to limit the minimum start-up and maximum operating voltage detected through the VOLTAGE MONITOR pin. An external peak detector consisting of a diode and capacitor are required to provide input line peak voltage to the VOLTAGE MONITOR pin through a resistor. At power up, I UV+ keeps the LinkSwitch-PH off until the input line voltage reaches the undervoltage threshold. At power down, I UV- prevents restart attempts after the output goes out of regulation. The same resistor used for UV also sets line overvoltage (OV) shutdown threshold which, once exceeded, forces the LinkSwitch-PH to stop switching (after completion of the current switching cycle). Once the line voltage returns to normal, the device resumes normal operation. A small amount of hysteresis is provided on the OV threshold to prevent noise triggering. When the power FET is off, the rectified DC high voltage surge capability is increased to the voltage rating of the power FET (725 V), due to the absence of the reflected voltage and leakage spikes on the drain. Hysteretic Thermal Shutdown The thermal shutdown circuitry senses the controller die temperature. The threshold is set at 142 °C typical with a 75 °C hysteresis. When the die temperature rises above this threshold (142 °C) the power FET is disabled and remains disabled until the die temperature falls by 75 °C, at which point the power FET is re-enabled. Safe Operating Area (SOA) Protection The device also features a safe operating area (SOA) protection mode which disables FET switching for 40 cycles in the event the peak switch current reaches the ILIMIT threshold and the switch on-time is less than t ON(SOA). This protection mode protects the device under short-circuited LED conditions and at start-up during the soft-start period when auto-restart protection is inhibited. The SOA protection mode remains active in normal operation. PI-5435-052510 D S BP V R FB CONTROL |
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