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WS9822BS7P Datasheet(PDF) 6 Page - List of Unclassifed Manufacturers |
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WS9822BS7P Datasheet(HTML) 6 Page - List of Unclassifed Manufacturers |
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6 / 11 page  www.winsemi.com Tel : +86-755-8250 6288 Fax : +86-755-8250 6299 6/11 WS9822B Product Description WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS WINSEMI MICROELECTRONICS Function Description The WS9822B is a three-stage dimming constant current LED driver with high precision and is applied to non-isolated buck LED power system. The WS9822B integrates a switcher dimming circuit and can change the output current through shifting external switcher ON/OFF to perform the dimming function. The WS9822B is compatible the PCB board with mainstream non-dimming products in the markets, such as WS3442, thus it can achieve the seamless upgrades from non-dimming to ON/OFF dimming. Switcher Dimming Control The switcher is opened first and closed again when the dimming is required, and the output current changes in accordance with the presetted current. The switching time should be more than 500mS. The dimming current cyclically varies in the sequence of 100% to 40% to15%. The reset time is 5S. So it is a normal dimming if the time interval of the switch from turn-off to turn-on is less than 5s; otherwise it will be considered as a reset signal. The output current reaches up to 100% after the switch is on again whatever the output stage of the preceding current is. Start Up The VCC capacitor will be charged through the start-up resistor when the system is powered on. When the VCC pin voltage reaches the turn on threshold, the internal circuits start operating. The WS9822B integrates the 16V ZENER for clamping the VCC. The typical value of the start-up current is 130uA (the maximum value is 195 uA). For the application of 176VAC— 264VAC, the start-up resistor can be calculated by the equation（ 1）: _ min _ max 1.414 176 1.414 1.27M 195 in st st V V R I uA （1） The start-up resistor can be chosen from 720K Ω to 1.2MΩ. Two resistors in 1206 size SMD or 1/4W metal film resistors can be used in series. Due to the ultra-low operating current, the auxiliary winding is not needed to supply the IC. 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 4.7uF/25V electrolytic capacitor can be used to Vcc Pin. If selecting MLCC, the material of X7R will be used to satisfy the stability of the capacity under high temperature. Due to external damage resulted from small volume and brittle texture of MLCC, it is easy to cause Vcc currents leakage, which will make the WS9822B unable to start. Strict control measures are taken in the layout and productive process. In order to avoid the return flickering and the disorder time, the Vcc capacitor should be in parallel with discharge resistor, which value should be chosen from 150KΩ to 240KΩ. Constant Current Control Utilizing proprietary current control method, the WS9822B can achieve precise LED output current with a few external components. Cycle by Cycle current sense is adopted in WS9822B, 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 （ 2）: ) ( 4 . 0 mA R I cs PK （ 2） Where, RCS is the current sense resistor value. The current in LED can be calculated by the equation（ 3）: ) ( 2 mA I I PK LED （ 3） Where, IPK is the peak current of the inductor. Freewheeling Diode The diode will b ear the reverse voltage equal to the input voltage when the MOSFET is on. A 600V diode was |
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