RT8457AGS Richtek

RT8457A Isolated Secondary-Side LED Lighting Dimmable Current Controller General Description Features zz z zz Secondary-Side LED Current Regulation The RT8457A is an isolated secondary LED current zz z zz High Accuracy 170mV LED Current Threshold controller designed specifically for lighting fixtures such Control as E27, GU10, T5 and T8 that require power line isolation zz z zz 0.5mA Operating Current for safety and reliability, and that require high conversion zz z zz Adjustable LED Current efficiency as well as high LED current accuracy. zz z zz Precision Secondary-Side LED Current Dimming The RT8457A contains 1) a constant current regulating zz z zz Precision Analog Dimming at Secondary-Side amplifier with 170mV threshold used to program the LED zz z zz Output Over-Voltage Protection string current with a simple resistor to within 5% LED zz z zz SOP-8 Package current accuracy 2) an over-voltage comparator to protect zz z zz RoHS Compliant and Halogen Free the output when LED string is open or broken and 3) an opto-coupler driver to control the primary-side of the transformer to complete the system loop. Applications Precise dimming is achieved by controlling the LED current z Isolated LED Lighting Fixtures at the secondary-side via analog dimming. Applying a z E27/GU10/T5/T8 LED Lamp voltage greater than 1.1V at the ACTL pin will set the LED current sense threshold between the LED and GND pins Marking Information at the highest level (around 170mV). The maximum LED RT8457AGS : Product Number current is adjustable by the sense resistor between the RT8457A YMDNN : Date Code LED and GND pins. Lowering the ACTL pin voltage will GSYMDNN reduce the LED current sense threshold. The RT8457A is available in the SOP-8 package. Simplified Application Circuit D1 V OUT Opto-Coupler Secondary-Side C1 Winding R LED VCC R1 REF OUT RT8457A LED String C2 OVP R2 Dimming ACTL Control GND LED R S Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8457A-02 September 2013 www.richtek.com 1RT8457A Ordering Information Pin Configurations (TOP VIEW) RT8457A Package Type 8 VCC NC S : SOP-8 2 7 REF ACTL Lead Plating System 3 6 OUT LED G : Green (Halogen Free and Pb Free) 4 5 GND OVP Note : SOP-8 Richtek products are : RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Functional Pin Description Pin No. Pin Name Pin Function Supply Voltage Input. A 0.1 F bypass capacitor should be connected between VCC 1 VCC and GND. Internal Reference Voltage. A 0.1 F bypass capacitor is required between this pin and 2 REF GND. Open-Collector Output. Connect this pin to an opto-coupler with a current limiting 3 OUT resistor. 4 GND Ground. 5 OVP Over-Voltage Protection Sense Input with 1V Threshold. LED Current Sense Input. The sense threshold is 170mV when ACTL pin voltage is 6 LED higher than 1.1V. The threshold can be adjusted by the ACTL pin. Analog Dimming Control Input. The LED current sense threshold is at the maximum 7 ACTL when the ACTL pin voltage is higher than 1.1V. Must place a 100k from the ACTL pin to GND to avoid the noise interference. 8 NC No Internal Connection. Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8457A-02 September 2013 2