LM3464_1

LM3464 and LM5021 DHC 25W Reference Designs LM3464 and LM5021 DHC 25W Reference Designs National Semiconductor Application Note 2102 David Zhang March 31, 2011 Introduction This evaluation board consists of a National Semiconductor LM5021 based 120Vac 24W AC/DC flyback converter and a LM3464 based dynamic head room control (DHC) four channel LED driver IC. This demonstration platform was developed so that the customers could evaluate the LM3464 with an AC/DC supply. Once familiar with the operation of the LM3464 and its control of the AC/DC converter's control loop, the type of AC/DC power supply and the converter's output power becomes less relevant. The evaluation board contains eight CREE XLamp MC-E LEDs. Each XLamp MC-E LED has four separate LEDs in each package for a total of 32 LEDs. The CREE MC-E LED allows for an easy demonstration of the LM3464 four channel operation with eight packaged LEDs. each LED string is regulated to 200mA. A heat sink is mounted on the back of the PCB to dissipate the heat generated by the LEDs.The LM3464 regulates each LED string current and adjust the secondary output voltage of the AC/DC power supply 0.9V above the LED string forawrd voltage.The LM3464 monitors the output voltage and adjusts the feedback voltage to the LM5021 primary control. This evaluation also demonstreates the LM3464 thermal fold-back feature which reduces the average LED current when the LED temperature is over 80°C. The AC/DC flyback power supply works in the discontinuous conduction mode and achieves power factor (PF) greater than 0.98. The schematic, bill of materials, layout and measured performance characteristics are included. Key Features • • • • • • Drive four strings of LEDs from 120Vac Overall Efficiency greater than 82% DC/LED Efficiency greater than 90% Power Factor greater than 0.98 Dynamic Headroom Control (DHC) Thermal foldback control Performance Specifications Symbol VIN VOUT ILED POUT fsw Parameter Input voltage LED string voltage LED string average current per string Output power Switching frequency Min 90 VRMS 22 V Typ 120 VRMS 26 V 200 mA 21 W 67 kHz Max 132 VRMS 30 V - AN-2102 © 2011 National Semiconductor Corporation 301439 www.national.com AN-2102 Demo Board 30143905 www.national.com 2 AN-2102 LM3464 120VAC, 24W Isolated 4 LED Driver Demo Board Schematic 30143901 Warning: The LM3464 evaluation board has exposed high voltage components that present a shock hazard. Caution must be taken when handling the evaluation board. Avoid touching the evaluation board and removing any cables while the evaluation board is operating. Warning: The ground connection on the evaluation board is NOT referenced to earth ground. If an oscilloscope ground lead is connected to the evaluation board ground test point for analysis and the mains AC power is applied (without any isolation), the fuse (F1) will fail open. For bench evaluation, either the input AC power source or the bench measurement equipment should be isolated from the earth ground connection. Isolating the evaliation board (using 1:1 isolation line isolation transformer) rather than the oscilloscope is highly recommended. 3 www.national.com AN-2102 Bill of Materials Designator C1 C2 C3, C18 C4 C5, C14,C15 C6, C13 C7 C8, C16 C9, C10 C11 C12 C17 C19 D1 D2, D7 D3 D4 D5 D6 D8 F1 H1 J1, J2, J3, J4, J5, J6, J12 Description CAP .10UF 305VAC EMI SUPPRESSION CAP, CERM, 0.33uF, 50V, +/-10%, X7R, 0805 CAP, CERM, 0.22uF, 250V, +/-10%, X7R, 1210 CAP, 33UF, 35V, ELECT, 5mmx11mm CAP, CERM, 0.22uF, 100V, +/-10%, X7R, 0805 CAP, CERM, 1uF, 25V, +/-10%, X5R, 0805 CAP, CERM, 47pF, 50V, +/-5%, C0G/NP0, 0805 CAP, CERM, 0.068uF, 50V, +/-10%, X7R, 0805 CAP, 1000UF, 35V, ELECT, 12.5mmx25mm CAP, CERM, 1000pF, 250VAC, +/-10%, X7R, 1808 CAP, CERM, 0.15uF, 50V, +/-10%, X7R, 0805 CAP, CERM, 1uF, 50V, +/-10%, X7R, 1206 CAP, CERM, 220pF, 500V, +/-10%, X7R, 1206 Diode, Switching-Bridge, 400V, 0.8A, MiniDIP Diode, Schottky, 100V, 0.2A, SOD-123 DIODE TVS 150V 600W UNI 5% SMA DIODE, 1000V, 1A, Mini SMA Diode, Schottky, 100V, 2A, SMB Diode, Zener, 10V, 500mW, SOD-123 Diode, Zener, 8.2V, 500mW, SOD-123 CMHZ4694 Heat Sink Terminal, Turret, TH, Double Manufacturer EPCOS MuRata MuRata Panasonic MuRata AVX Yageo America AVX Panasonic Syfer Technology Murata TDK Vishay Diodes Inc. Part Number B32921C3104M GRM219R71H334KA88D GRM32DR72E224KW01L EEUFM1V330 GRM21AR72A224KAC5L 08053D105KAT2A CC0805JRNP09BN470 08055C683KAT2A EEU-FC1V102 1808JA250102KXBSY2 GRM21BR71H154KA01L C3216X7R1H105K VJ1206Y221KXEAT5Z HD04-T ST BAT41ZFILM Microelectronics Littlefuse Comchip Technology Diodes Inc. ON Semiconductor Central Semiconductor Cooper/ Bussman CUI Inc. Keystone Electronics Keystone Electronics Samtec Coilcraft Coilcraft Cree Fairchild Semiconductor Fairchild Semiconductor Fairchild Semiconducto Vishay-Dale Vishay-Dale Vishay-Dale Panasonic Vishay/Dale Vishay/Dale Vishay/Dale Vishay-Dale 4 SMAJ150A CGRM4007-G B2100-13-F MMSZ4697T1G CMHZ4694 6125FA1A VHS-45 1502-2 5016 TSW-102-07-G-S BU09-103R25BL MSS1038-105KLB MCE4WT-A2-0000-000M02 FDD6N50TM MMBT3904 FDD3682 CRCW1206150KFKEA CRCW0805100KFKEA CRCW080510R0FKEA ERJ-8RSJR10V CRCW060310K5FKEA CRCW08051K00FKEA CRCW08055K11FKEA CRCW080510K0FKEA J7, J8, J9, J10, Test Point, SMT J11 JP1, JP2, JP3 Jumper L1 L2 LED1 - LED8 Q1 Q2 Common Mode Choke, 10mH, 0.3A Inductor, Shielded Drum Core, 1mH, 0.45A,SMD LED MOSFET, N-CH, 500V, 6A, DPAK Transistor, NPN, 40V, 0.2A, SOT-23 Q3, Q4, Q5, Q6 MOSFET, N-CH, 100V, 32A, DPAK R1 R2 R3, R4 R5 R7 R8, R12 R9 R10, R11 www.national.com RES, 150k ohm, 1%, 0.25W, 1206 RES, 100k ohm, 1%, 0.125W, 0805 RES, 10.0 ohm, 1%, 0.125W, 0805 RES, 0.1 ohm, 5%, 0.25W, 1206 RES, 10.5k ohm, 1%, 0.1W, 0603 RES, 1.00k ohm, 1%, 0.125W, 0805 RES, 5.11k ohm, 1%, 0.125W, 0805 RES, 10.0k ohm, 1%, 0.125W, 0805 AN-2102 Designator R13 R14, R15 R16 R18 R19 R20 Description RES, 105k ohm, 1%, 0.1W, 0603 RES, 25.5k ohm, 1%, 0.125W, 0805 RES, 2.67k ohm, 1%, 0.125W, 0805 RES, 3.01k ohm, 1%, 0.125W, 0805 RES, 8.06k ohm, 1%, 0.125W, 0805 RES, 0 ohm, 5%, 0.125W, 0805 Manufacturer Vishay-Dale Vishay-Dale Vishay-Dale Vishay-Dale Vishay-Dale Vishay-Dale Vishay-Dale Vishay-Dale Vishay-Dale Panasonic National Semiconductor National Semiconductor NEC National Semiconductor Littlefuse Part Number CRCW0603105KFKEA CRCW080525K5FKEA CRCW08052K67FKEA CRCW08053K01FKEA CRCW08058K06FKEA CRCW08050000Z0EA CRCW08051R00FKEA CRCW12060000Z0EA CRCW080522K1FKEA ERT-J1VG103GA LM5021MM-1 LM3464MH PS2501L-1-Q-A LMV431AIMF V150LA5P R21, R22, R23, RES, 1.0 ohm, 1%, 0.125W, 0805 R24 R25 R26 RT1 T1 U1 U2 U3 U4 VR1 RES, 0 ohm, 5%, 0.25W, 1206 RES, 22.1k ohm, 1%, 0.125W, 0805 Thermistor NTC, 10k ohm, 2%, 0603 Transformer, Flyback, 540UH AC-DC Current Mode PWM Controller Dynamic Headroom Controller w/Therm Control Opto Coupler Low-Voltage Adjustable Precision Shunt Regulator Varistor, 150V, 25J, 10mm Wurth Elektornik 750311959 5 www.national.com AN-2102 Typical Performance Characteristics Efficiency vs. Line Voltage 85 84 83 EFFICIENCY (%) 82 81 80 79 78 77 76 75 90 100 110 120 130 INPUT VOLTAGE (VAC) 140 30143938 Power Factor vs. Line Voltage 1.000 0.995 0.990 POWER FACTOR 0.985 0.980 0.975 0.970 0.965 0.960 0.955 0.950 90 100 110 120 130 INPUT VOLTAGE (VAC) 140 30143939 Total LED Current vs. LED Temperature 1.00 0.95 TOTAL LED CURRENT (A) 0.85 0.80 0.75 0.70 0.65 0.60 0.56 0.50 77 79 81 83 85 87 89 LED TEMPERATURE (C) 91 30143940 Output Voltage & LED Forward Voltage vs. LED Temperature 26.5 OUTPUT VOLTAGES (V) 26.0 25.5 25.0 VLED 24.5 24.0 23.5 30 40 50 60 70 LED TEMPERATURE (C) 80 30143941 0.90 Vout Line Voltage and Line Current (VIN = 120VRMS) Output Voltage and LED Current (VIN = 120VRMS) 30143918 30143920 Ch1: Line Voltage (100 V/div); Ch3: Line Current (200 mA/div); Time (10 ms/div) Ch1: Output Voltage (10 V/div); Ch3: Total LED Current (500 mA/div); Time (10 ms/div) www.national.com 6 AN-2102 Power MOSFET Q1 Drain to Source Voltage (VIN = 120VRMS) Start Up Voltage and Current (VIN=120VRMS) 30143921 30143922 Ch1: Drain Voltage (100V/div) Time (4 µs/div) Ch1: Output Voltage (10 V/div); Ch3: Total LED Current (500 mV/div); Time (100 ms/div) 7 www.national.com AN-2102 PCB Layout 30143907 Top Layer 30143908 Bottom Layer www.national.com 8 AN-2102 Design Information 1ST STAGE - DCM FLYBACK The evaluation board is considered a two stage LED driver system. The first stage is the AC/DC flyback converter and the second stage is the LM3464 LED currenr regulator. The first stage employs a NSC LM5021-1 in a discontinuous mode flyback and operates at fixed switching frequency and constant duty cycle. The input current follows the rectified AC input voltage and achieves power factor of 0.98 and higher. To ensure LM5021-1 operates at constant duty cycle, R7 and R1 need to be properly sized so that the slope compensation ramp is bigger than the current sense voltage. In this design, R7 is chosend to be 10.5Kohm and R1 is chosen to be 0.1 ohm. At 40% duty cycle, the peak ramp voltage is 246mV and the peak current sense voltage is around 150mV. The transformer is designed to keep the flyback converter operating in discontinuous mode at peak output power. For a single stage PFC flyback converter, the peak output power occurs at peak input voltage and is twice the average output power. The transformer used in the evaluation board can handle up to 48W peak output power without saturation. The feedback loop of the flyback converter includes U4 the LMV431 shunt regulator and U3 the opto coupler. When LM3464 is not controlling the output voltage (during initial power up), the flyback converter output voltage is set by resistor divider R13, R26 and R11 (approximately 17V). Once the LM3464 begins to control the LM5021 and therefore the output voltage by sink/source current through OutP pin and pushes the output voltage up to as high as 33V. In order to have good power factor, the control loop bandwidth has to be lower than 120Hz. For further explanation of LM3464 operation, please refer to thr LM3464 datasheet. 2ND STAGE - DYNAMIC HEADROOM CONTROL The second stage of the evaluation board features the LM3464 which is a linear LED driver controller. The LM3464 is a four string controller, and in this particular demonstration board the LM3464 controls four strings of eight LEDs at 200mA. The internal ampiliers of LM3464 compare the voltages of the current sense resistors to a 200mV reference voltage and control the gate voltages of four external MOSFETs ( Q3 - Q6 ) to achieve linear current regulations. The voltage headroom which the voltage difference between the seondary output voltage of the AC/DC power supply and the LED string forward voltage is minimized by the LM3464 controller.By minimizing this voltage, the efficiency of the system is maximized. The LM3464 regulates the drain voltage of the external MOSFET to the voltage of the VDHC pin which is equal to 0.9V, therefore the headroom is about 0.9V. LM3464 has thermal fold-back function to prevent the LEDs from overheating. When the voltage at the thermal pin ( pin #3 ) is less than 3.25V, the average LED current is reduced by PWM dimming. For this evaluation board, the thermal foldback function starts to kick in when the resistance of the NTC thermistor RT1 reaches 3.2kohm. JUMPER/FAULT INFORMATION Jumpers JP1, JP2 and JP3 are provided for the customers to short or disconnect LED strings. One string of LED can be disconnected to the power supply by open connector JP1. One LED each on LED string number one can be shorted by short connctors JP2 or JP3. LM3464 will continue to regulate the currents of the remaining strings of LEDs when one or more strings of LEDs are shorted or disconnected. It will also continue to regulate the LED current when one or more LEDs in that string are shorted. Electromagnetic Interference (EMI) In order to get a quick estimate of the EMI filter performance, only the PEAK conductive EMI scan was measured and the data was compared to the Class B conducted EMI limits published in FCC – 47, section 15. 30143932 FIGURE 1. Peak Conductive EMI scan per CISPR-22, Class B Limits 9 www.national.com AN-2102 Thermal Analysis The board temperature was measured using an IR camera (HIS-3000, Wahl) while running under the following conditions: VIN = 120 VRMS The results are shown in the following figure. 30143933 FIGURE 2. Top Side Thermal Scan www.national.com 10 AN-2102 11 www.national.com LM3464 and LM5021 DHC 25W Reference Designs Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Amplifiers Audio Clock and Timing Data Converters Interface LVDS Power Management Switching Regulators LDOs LED Lighting Voltage References PowerWise® Solutions Temperature Sensors PLL/VCO www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/vref www.national.com/powerwise WEBENCH® Tools App Notes Reference Designs Samples Eval Boards Packaging Green Compliance Distributors Quality and Reliability Feedback/Support Design Made Easy Design Support www.national.com/webench www.national.com/appnotes www.national.com/refdesigns www.national.com/samples www.national.com/evalboards www.national.com/packaging www.national.com/quality/green www.national.com/contacts www.national.com/quality www.national.com/feedback www.national.com/easy www.national.com/solutions www.national.com/milaero www.national.com/solarmagic www.national.com/training Applications & Markets Mil/Aero PowerWise® Design University Serial Digital Interface (SDI) www.national.com/sdi www.national.com/wireless www.national.com/tempsensors SolarMagic™ THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS, IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS. EXCEPT AS PROVIDED IN NATIONAL’S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE AND/OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: Life support devices or systems are devices which (a) are intended for surgical implant into the body, or (b) support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness. National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. Copyright© 2011 National Semiconductor Corporation AN-2102 For the most current product information visit us at www.national.com National Semiconductor Americas Technical Support Center Email: support@nsc.com Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Technical Support Center Email: europe.support@nsc.com National Semiconductor Asia Pacific Technical Support Center Email: ap.support@nsc.com National Semiconductor Japan Technical Support Center Email: jpn.feedback@nsc.com