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WS3414HD7P Datasheet(PDF) 5 Page - Shenzhen Winsemi Microelectronics Co., Ltd |
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WS3414HD7P Datasheet(HTML) 5 Page - Shenzhen Winsemi Microelectronics Co., Ltd |
5 / 8 page www.winsemi.comTel : +86-755-8250 6288 Fax : +86-755-8250 6299 5/8 WS3414H ProductDescription WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS Application Information The WS3414H is a high precision Active PFC driver integrating 650V power MOSFET, specially designed for non-isolated buck offline constant current LED lighting. Operating in critical conduction mode, the driver achieves high power factor, low THD and high efficiency. Start Up After system powered up, the VCC pin capacitor is charged up by the start up resistor. When the VCC pin voltage reaches the turn on threshold, the internal circuits start working. The COMP pin voltage is pulled up to 1.5V quickly, then the WS3414Hstarts switching. The system works at 10k Hz frequency at the beginning, the COMP voltage rises up gradually, and the inductor peak current also rises up. The LED current hence achieves a soft start without overshoot. After the output voltage is built up, the VCC power is supplied by the output voltage through a diode. The maximum value of the startup current is 100uA. For the application of 85VAC—264VAC, the startup resistor can be calculated by the equation: Ω K uA V I V R st in st 850 100 85 max _ min _ Constant Current Control The WS3414H utilizes floating ground structure. The inductor current is sensed during the whole switching cycle, thus it achieves high precision output current control and also excellent line and load regulation. The current in LED can be calculated by the equation: Rcs mV R V I CS CS O 200 Rcs is the current sensing resistor. Feedback Network The WS3414H senses the output current zero crossing information through the feedback network, the FB falling threshold voltage is set to 0.2V with 0.15V hysteresis. The FB pin is also used to detect output OVP, the threshold voltage is 1.6V. The ratio of FB upper resistor to lower resistor can be set as: OVP FBH FBL FBL V V R R R 6 . 1 Where, RFBL: The lower resistor of the feedback network RFBH: The upper resistor of the feedback network VOVP: Output over voltage setting point The minimum VOVP should be set about 1.3Vo.It is recommended that the FB lower resistor is set to 3.3KΩ—5.1KΩparalleled with a 22pF ceramic capacitor. Protection Functions The WS3414H offers rich protection functions to improve the system reliability. When the LED is open circuit, the output voltage will gradually rise up. The output voltage is sensed by the FB pin when power MOSFET is turned off. When FB voltage reaches the OVP threshold, it will trigger fault logic and the system stops switching. When the LED is shorted circuit, the system will work under 10k Hz switching frequency. Meanwhile, the output voltage is low and the VCC pin cannot be charged up by the output voltage, so the VCC pin voltage will gradually decrease and finally reaches the UVLO threshold. After the system enters into fault condition, the VCC voltage will decrease until it reaches UVLO threshold. Then the system will re-start again. If the fault condition is removed, the system will resume normal operation. When the output is short circuit or the inductor is saturated, the CS peak voltage will be relatively high. When CS voltage reaches the internal limitation (1V), the power MOSFET will be turned off instantaneously. This cycle by cycle current limitation can help protecting the power MOSFET, the inductor and the output diode. Thermal Regulation The WS3414H integrates thermal regulation function. When the system is over temperature, the output current is gradually reduced; the output power and thermal dissipation are also reduced. The system temperature is regulated and the system reliability is improved. The thermal regulation temperature is set to 150℃ internally. PCB Layouts The following guidelines should be followed in WS3414H PCB layout: |
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