® RT8486 Isolated Secondary-Side Lighting LED Controller General Description Features The RT8486 is an isolated secondary-side lighting LED controller designed specifically for lighting fixtures such as E27, GU10, T5 and T8. The IC is suitable for applications that require power line isolation for safety, reliability, high conversion efficiency, as well as high LED current accuracy. z Secondary-Side LED Current Regulation z 4.75V to 48V Operating Input Range High Accuracy LED Current Threshold Control 0.6mA Operating Current Adjustable LED Current Output Over-Voltage Protection Small SOT-23-6 Package RoHS Compliant and Halogen Free z z z z The RT8486 contains 1) a constant current regulating amplifier with 140mV threshold used to program the LED string current with a simple resistor to within 5% LED current accuracy; 2) an over-voltage comparator to protect the output when LED string is open or broken; 3) an optocoupler driver to control the primary-side of the transformer to complete the system loop. z z Applications z z Isolated LED Lighting Fixtures E27/GU10/T5/T8 Marking Information The RT8486 is offered in the small SOT-23-6 package. 06= : Product Code 06=DNN Ordering Information DNN : Date Code RT8486 Package Type E : SOT-23-6 Pin Configurations (TOP VIEW) Lead Plating System G : Green (Halogen Free and Pb Free) VCC OUT CP Note : 6 Richtek products are : ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` 5 4 2 3 CN GND OVP Suitable for use in SnPb or Pb-free soldering processes. SOT-23-6 Simplified Application Circuit D1 VOUT Opto-Coupler VCC Secondary side winding R1 RLED RT8486 RVC1 CVC1 OUT CVCC LED String OVP RIC1 GND CP CN R2 CIC1 RCN RSENSE Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8486-00 April 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8486 Typical Application Circuit & Function Block Diagram D1 VOUT Opto-Coupler VCC RLED R1 RT8486 Secondary side winding CVCC LED String OUT 2.5V - CV RVC1 CVC1 + OVP 140mV - CC RIC1 + R2 CIC1 CP CN GND RCN RSENSE Operation The operation input voltage range is from 4.75V to 48V for the RT8486. An internal 2.5V reference voltage is generated from VCC input power for internal bias voltage. The RT8486 is used to clamp the transformer secondary-side output voltage by the CV control loop and regulate the LED string current by the CC control loop at the same time. The transformer secondary-side output voltage can be monitored by the OVP pin. The sensed OVP pin voltage is compared with the 2.5V internal reference. When the OVP pin voltage is higher than 2.5V, the OUT pin starts to sink more current to allow the external opto-coupler and controller at primary-side to reduce the power output to transformer secondary. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 The LED string current can be regulated by the CN pin voltage through the current sense resistor connected between the CN and CP pins. The CN pin voltage is compared with the 140mV internal reference. When the CN pin voltage is greater than 140mV, the OUT pin will sink more current to adjust the LED current through an external opto-coupler and controller at primary-side. is a registered trademark of Richtek Technology Corporation. DS8486-00 April 2013 RT8486 Functional Pin Description Pin No. Pin Name Pin Function 1 CN Non-Inverting Input of the CC Regulating Amp. It has a offset from the CP pin. The CN pin should be connected to the "Current In" node of the current sensing resistor, RSENSE. 2 GND Ground. This pin should be connected to the ground of the secondary-side. 3 OVP Over-Voltage Protection Sense Input with Threshold of 2.5V. 4 CP Inverting Input of the CC Regulating Amp. It has a offset from the CN pin. The CP pin connects to a resistor to set LED current. 5 OUT Open-Collector Output. Connect this pin to an opto-coupler with a current limiting resistor. 6 VCC Supply Voltage Input. A 0.1μF bypass capacitor should be connected between VCC and GND. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8486-00 April 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8486 Absolute Maximum Ratings z z z z z z z z z z (Note 1) VCC, OUT to GND ---------------------------------------------------------------------------------------------------------CP to GND ------------------------------------------------------------------------------------------------------------------CN to GND -------------------------------------------------------------------------------------------------------------------OVP to GND ----------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOT-23-6 --------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOT-23-6, θJA ---------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions z z z −0.3V to 52V −0.6V to 1V −0.3V to 1V −0.3V to 6V 0.48W 208.2°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VCC (Note5) --------------------------------------------------------------------------------- 4.75V to 48V Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VCC = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Quiescent Current ICC V CN = VCP = 0V -- 550 -- μA GND Pin Current IGND V CN = VCP = 0V, GND = 0V -- 530 -- μA OVP Voltage V OVP V CN = VCP = 0V 2.46 2.5 2.54 V CN = VCP = 0V, T A = −25°C to 105°C 2.45 -- 2.55 OVP Input Bias Current IOVP -- -- 100 LED Current Sensing Amplifier Threshold V CN−CP V OVP = 2.4V 135 141 147 V OVP = 2.4V, TA = −25°C to 105°C 134 -- 149 -- -- 200 nA -- 8 -- mA CN Input Bias Current OUT Maximum Sink Current V OVP = 2.4 to 2.6V ICN IOUT V OUT = 1.5V V nA mV Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. RT8486 starts regulation at VCC ≥ 4.5V, and meets all parameter specs at VCC ≥ 4.75V. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8486-00 April 2013 RT8486 Typical Operating Characteristics VOVP vs. Temperature ICC vs. Temperature 2.52 680 VCC VCC VCC VCC 640 45V 36V 12V 4.75V 2.51 VCC VCC VCC VCC 2.50 VOVP (V) I CC (µA) 600 = = = = 560 520 = = = = 45V 36V 12V 4.75V 2.49 2.48 480 2.47 440 2.46 400 -50 -25 0 25 50 75 100 -50 125 -25 0 50 75 100 125 Temperature (°C) Temperature (°C) VOUT vs. Temperature IOVP vs. Temperature 1.0 50 0.9 45 35 30 = = = = 45V 36V 12V 4.75V 0.8 0.7 VOUT (V) VCC VCC VCC VCC 40 I OVP (nA) 25 25 20 0.5 0.3 10 0.2 5 0.1 0 0.0 -25 0 25 50 75 100 = = = = 45V 36V 12V 4.75V 0.4 15 -50 VCC VCC VCC VCC 0.6 IOUT = 2mA -50 125 -25 0 25 50 75 100 125 100 125 Temperature (°C) Temperature (°C) IOUT vs. Temperature VCN-CP vs. Temperature 146 10 9 144 8 VCN-CP (mV) I OUT (mA) 7 6 VCC VCC VCC VCC 5 4 3 = = = = 45V 36V 12V 4.75V 2 142 VCC VCC VCC VCC 140 = = = = 45V 36V 12V 4.75V 138 136 1 134 0 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8486-00 April 2013 125 -50 -25 0 25 50 75 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8486 Application Information Output Voltage Setting Compensation The voltage control loop is controlled via the first transconductance operational amplifier. An opto-coupler which is directly connected to the output and an external resistor bridge is connected between the output positive line and the ground reference. The middle point is to be connected to the OVP pin of the RT8486, where R2 is the upper resistor and R1 is the lower resistor of the bridge. The relationship between R2 and R1 is shown as the equation below : (R1+ R2 ) VOUT = VOVP × R2 ( V − VOVP ) R1 = R2 × OUT VOVP Both the voltage control transconductance amplifier and the current control transconductance amplifier can be fully compensated. The output and negative inputs are directly accessible for external compensation components, as shown in the Typical Application Circuit. where VOUT is the desired maximum output voltage. To avoid discharge of the load, the resistor bridge R1, R2, should be highly resistive. For this type of application a total value of 100kΩ (or more) would be appropriate for the resistors R1 and R2. As an example, with R1 = 80kΩ and R2 = 20kΩ, VOUT = 12.5V. Output Current Setting The current control loop is controlled via the second transconductance operational amplifier. An opto-coupler and the sense resistor, RSENSE, is placed in series on the output negative line. VCN−CP threshold is achieved externally by a resistor bridge tied to the reference voltage, VREF. Its middle point is tied to the positive input of the current control operational amplifier and its foot is connected to the lower potential point of the sense resistor. The resistors of the bridge are matched to provide the best precision. With VCN−CP and RSENSE, the expected output current, IOUT, can be obtained as the equation below : IOUT V = CN−CP RSENSE where IOUT is the desired maximum output current, and VCN−CP is the threshold voltage for the current control loop. Note that, the sense resistor, RSENSE, should be chosen taking into account its maximum power dissipation (PLIM) during full load operation. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 The typical component values for the compensation network of voltage control loop is CVC1 = 2.2nF and RVC1 = 22kΩ. The typical component values for the compensation network of current control loop is CIC1 = 2.2nF, RIC1 = 22kΩ and RCN = 1kΩ. However, in many application conditions, the current control loop can be stable without compensation network (RCN = 0, no CIC1 nor RIC1). When the voltage control loop is used as the voltage limit protection or the current control loop is used as the current limit protection, no compensation network is needed for the protecting control loop. A resister, ROPT, must be connected in series with the opto-coupler since it is part of the compensation network. Although the value of ROPT is not critical, it's recommended to be in the range from 0.33kΩ to (VOUT − 2) / (0.005)Ω. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For SOT-23-6 package, the thermal resistance, θ JA, is is a registered trademark of Richtek Technology Corporation. DS8486-00 April 2013 RT8486 208.2°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (208.2°C/W) = 0.48W for SOT-23-6 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Layout Consideration For the best performance of the RT8486, the following PCB Layout guidelines must be strictly followed. ` Place the RSENSE resistor as close to the IC as possible. ` Keep the input/output traces as wide and short as possible. Secondary side winding D1 VOUT Optocoupler Maximum Power Dissipation (W)1 0.6 RLED Four-Layer PCB R1 0.5 RVC1 CVC1 0.4 CVCC RIC1 : : LED String : CIC1 0.3 VCC OUT CP 0.2 6 5 4 2 3 GND 0.1 CN GND OVP 0.0 0 25 50 75 100 R2 125 RCN Ambient Temperature (°C) Figure 1. Derating Curve of Maximum Power Dissipation RSENSE Figure 2. PCB Layout Guide Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8486-00 April 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8486 Outline Dimension H D L C B b A A1 e Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.889 1.295 0.031 0.051 A1 0.000 0.152 0.000 0.006 B 1.397 1.803 0.055 0.071 b 0.250 0.560 0.010 0.022 C 2.591 2.997 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 SOT-23-6 Surface Mount Package Richtek Technology Corporation 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. www.richtek.com 8 DS8486-00 April 2013