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WS9442 Datasheet(PDF) 5 Page - List of Unclassifed Manufacturers |
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WS9442 Datasheet(HTML) 5 Page - List of Unclassifed Manufacturers |
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5 / 9 page  www.winsemi.com Tel : +86-755-8250 6288 Fax : +86-755-8250 6299 5/9 WS9442 Product Description WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS Function Description The WS9442 is a high performance non-isolated buck converter specially designed for LED lighting. The device integrates a 500V power MOSFET. With the help of advanced constant current control and gate drive technology, the converter achieves excellent constant current performance with very few external components. It does not need auxiliary winding for powering the IC or voltage sensing, hence the system size and cost is greatly reduced. Start Up After system powered on, 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 operating. The WS9442 integrates a 17V ZENER diode to clamp the VCC voltage. Due to the ultra-low operating current, the auxiliary winding is not needed to supply the IC. The typical value of the start-up current is 200uA (the maximum value is 300uA). For the application of 176VAC— 264VAC, the start-up resistor can be calculated by the equation: _ _ 1.414 176 1.414 820 300 IN MIN ST ST MAX V R K I Two resistors in 1206 size SMD can be used in series. VCC Capacitor Selection The Vcc capacitor is used to bypass noise to IC, so that to assure its stable operation, and should be as close as possible to the chip. A 1uF capacitor can be used in Vcc. If selecting MLCC, the material of X7R will be used to satisfy the stability of the capacity under high temperatures. Due to external damage resulted from small volume and brittle texture of MLCC, the Vcc is easy to leakage currents, which will make the WS9442 unable to start. Strict control measures are taken in its layout and productive process. Constant Current Control The WS9442 utilizes proprietary current control method. It can achieve precise LED output current with a few external components. Cycle by Cycle current sense is adopted in WS9442, the CS pin is connected to the current sense comparator, and the voltage on CS pin is compared with the internal 400mV reference voltage. The MOSFET will be switched off when the voltage on CS pin reaches the threshold. The CS comparator includes a 350ns leading edge blanking time. The peak inductor current is calculated by the equation: ) ( 400 mA R I CS PK Where, RCS is the current sense resistor value. The current in LED can be calculated by the equation: ) ( 2 mA I I PK LED Where, IPK is the peak current of the inductor. Freewheeling Diode The diode will bear the reverse voltage equal to the input voltage when the MOSFET is on. A 600V diode was suggested to use. Besides, the operating frequency of freewheeling diode is from 20K to 120 KHz, such ultra fast recovery diodes as ES and ER whose Trr is less than 50ns are good choice. Input Electrolytic Capacitor Input voltage should be considered in to the capacitor pressure, and the common value is 400V. In general, the capacity design can be calculated by the following empirical equations: 90Vac~264Vac: 1W output uses1uF buck electrolytic capacitor; 176Vac~264Vac: 1W output uses 0.5uF buck electrolytic capacitor. Output Capacitor Electrolytic capacitor is recommended to be used. Its stable capacitance can improve the efficiency of power supply, the LED ripple current and luminous efficiency. Vovp voltage should be considered in output capacitor pressure. Inductor Selection |
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