LM5022LEDEVAL

User's Guide SNVA229A – October 2007 – Revised May 2013 AN-1605 LM5022 Boost LED Driver Evaluation Board 1 Specifications Of The Board This evaluation board has been designed to demonstrate the LM5022 low-side controller as a step-up (boost) regulator for delivering constant current to an array of high power LEDs. A complete schematic for all the components is shown in Figure 1. The board is two layers with components and power paths in 2oz. copper. The board is 62mil FR4 laminate and the Section 12 table lists all the components used in the example circuit. VIN = 10V to 14V L1 22 PH CIN1 CIN2 CINX 6.8 PF 6.8 PF 0.1 PF 0.2: RG Q1 RUV2 61.9 k: 1 CSYC OUT RT 100 pF 7 RT 56.2 k: RUV1 10 k: 10 OFF 3 UVLO SS LM5022 9 SYNC VIN COMP RS2 8 200: RS1 6 6.34 k: VCC FB 4 2 CF 100 : CCS 1 nF RCS 50 m: R2 20 k: 2.2 nF C2 6.04 k: C1 D2 U2 1 3 0.1 PF CSS R1 Q2 CO 4.7 PF CS GND COX 0.1 PF RFB2 0: 5 Vo/LED+ RSNS D1 RB 32.4 k: 2 RFB1 1.24 k: RZ 1.8 nF : GND/LED- 180 pF DIM Q3 RPD 10 k: Figure 1. Circuit Schematic 2 Example Circuit The example circuit which comes on the evaluation board powers ten series-connected white LEDs at a forward current, IF, of 1A ±10% from an input of 10V to 14V. White LEDs based on InGaN technology have a forward voltage, VF, of 3.0V to 4.0V, so the expected total output voltage is therefore 30V to 40V. The switching frequency is 300 kHz. Efficiency for the converter is 93% at an input voltage of 12.0V and an output current of 1.0A. All trademarks are the property of their respective owners. SNVA229A – October 2007 – Revised May 2013 Submit Documentation Feedback AN-1605 LM5022 Boost LED Driver Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 1 Powering The Converter www.ti.com Figure 2. Efficiency 3 Powering The Converter The input voltage should be connected between the VIN and GND terminals on the left side of the board. The series-connected chain of LEDs should be connected between the LED+ and LED- terminals or using connector J1 as shown in Figure 3. Solid 18 or 20 gauge wire with about 1 cm of insulation stripped away makes a convenient solderless connection to J1. P6 Cathode of Last LED C535676 Connector Anode of First LED P1 Figure 3. LED Connector 4 Enabling The Converter Once the input voltage has risen above the UVLO threshold of 9.0V the OFF* terminal controls the state of the converter. The LM5022 is disabled whenever the OFF* terminal is grounded. The LM5022 is enabled whenever the OFF* terminal is open-circuited. Upon enabling the LM5022 will perform a softstart, after which the output supplies constant current to the LEDs. * NOTE: OFF is an inverted logic input. 2 AN-1605 LM5022 Boost LED Driver Evaluation Board SNVA229A – October 2007 – Revised May 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated PWM Dimming www.ti.com 5 PWM Dimming The light output of LED arrays is often controlled or reduced with a PWM signal applied to the output current. This dimming method allows the converter to operate at a specific output current level (usually a set point determined by the LED manufacturer) instead of adjusting the average output current. The LM5022 boost LED evaluation board provides the DIM terminal as an input for PWM signals. DIM connects to the gate of a small MOSFET, Q3, that short-circuits or open-circuits the COMP pin of the LM5022. When the voltage at DIM is logic high, the converter output current is off. When the voltage at DIM is logic low, the converter output current is on. 6 Output Open-Circuit Protection The zener diode D2 provides protection in the case of an output open circuit. This can happen if the LED chain is disconnected or one of the LEDs fails as an open circuit while the LM5022 is powered. Open circuit is the most common LED failure mode, and it effectively disconnects the feedback path of the converter. Without protection a boost regulator-based LED driver would attempt to drive the output voltage beyond the limits of the external components. With D2 in the place, any output open circuit causes the output voltage to equal the breakdown of the zener diode plus the system feedback voltage of 1.25V. The minimum zener breakdown voltage should therefore be just higher than the maximum LED array voltage. For the example circuit, the minimum zener breakdown is 44.6V, providing a total output voltage of 46V or higher. Resistor Rfb1 limits the zener current to approximately 1 mA. 7 MOSFET Footprints The LM5022 boost LED evaluation board has a footprint for a single N-channel MOSFET with an SO-8 package using the industry standard pinout. (See Figure 4) This footprint can also accept thermally enhanced MOSFET packages that are compatible with SO-8 footprints. S D S D SO-8 S D G D Figure 4. SO-8 MOSFET Pinout 8 Testing The Converter Figure 5 shows a block diagram of connections for making measurements of efficiency. The wires used for making connections at the input should be rated to at least 5A of continuous current and should be no longer than is needed for convenient testing. A series ammeter capable of measuring 10A or more should be used for both the input and the output lines. Dedicated voltmeters should be connected with their positive and negative leads right at the four power terminals at the sides of the board. This measurement technique minimizes the resistive loss in the wires that connect the evaluation board to the input power supply and the LEDs. Output ripple current measurements should be taken with an oscilloscope and an AC current probe or AC-coupled DC current probe. This measurement can be taken anywhere in the loop formed by the LEDs and J1, however the recommended location is between the LED+/J1 connector and the anode of the first LED. SNVA229A – October 2007 – Revised May 2013 Submit Documentation Feedback AN-1605 LM5022 Boost LED Driver Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 3 Permanent Components www.ti.com Ammeter + Voltmeter V A VIN GND/ LED- GND Vo/ LED+ 12V, 5A Power Supply - LED10 V Ammeter Voltmeter A LED1 LM5022 Boost LED Evaluation Board Figure 5. Efficiency Measurement Setup 9 Permanent Components The following components should remain the same for any new circuits tested on the LM5022 boost LED evaluation board: 10 Name Value Cinx 0.1 µF Cf 1 µF Ccs 1 nF Rpd 10 kΩ Rs1 100Ω Additional Footprints The 100 pF capacitor Csyc provides an AC input path for external clock synchronization. Detection of the sync pulse requires a peak voltage level greater than 3.7V at the RT/SYNC pin. Note the DC voltage at RT is approximately 2V to allow compatibility with 3.3V logic. The sync pulse width should be set between 15 ns to 150 ns by the external components. The Rt resistor is always required, whether the oscillator is free running or externally synchronized. Rt must be selected so that the free-running oscillator frequency is below the lowest synchronization frequency. Footprint U2 and current limiting resistor Rz allow the user to add a shunt regulator voltage reference or zener diode to maintain tight control over the bias current through the right-hand transistor of Q2 as the output voltage changes. Tight regulation of the bias current allows better accuracy of the LED current. When using this method resistor Rb is re-selected to draw the 1 mA bias current using the following equation: Rb = (VZ – 0.6) / 0.001 (VZ is the zener or reference voltage) (1) The 0Ω placeholder Rz is re-selected to bias the zener/reference voltage and Q2 using the following: Rz = (VO-MIN - VZ) / (IZ + 0.001) (IZ is the zener/reference bias current) 4 AN-1605 LM5022 Boost LED Driver Evaluation Board (2) SNVA229A – October 2007 – Revised May 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Typical Performance Characteristics www.ti.com 11 Typical Performance Characteristics (TA = 25°C and VIN = 12V unless noted) Figure 6. Output Current Vs. Input Voltage Figure 7. Output Current Vs. Temperature 50 mA/DIV 200 mA/DIV IF IF SW 10V/DIV 2 és/DIV 2 és/DIV Figure 8. Switch Node Voltage DIM Figure 9. Output Current Ripple DIM 5V/DIV VCOMP 2V/DIV 5V/DIV VCOMP 2V/DIV 500 mA/DIV IF IF 40 és/DIV Figure 10. Dimming Response (IF Rising) SNVA229A – October 2007 – Revised May 2013 Submit Documentation Feedback 500 mA/DIV 20 és/DIV Figure 11. Dimming Response (IF Falling) AN-1605 LM5022 Boost LED Driver Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 5 Bill of Materials 12 www.ti.com Bill of Materials Table 1. Bill of Materials 6 ID Part Number Type Size Parameters Qty Vendor U1 LM5022 Low-Side Controller VSSOP-10 60V 1 Texas Instruments N-MOSFET SO-8 60V, 31mΩ, 27nC 1 Vishay Diodes, Inc U2 Not Used Q1 Si4850EY Q2 DMMT5401 Dual PNP SOT-26 150V, 300mW 1 Q3 TN0200K N-MOSFET SOT-23 20V, 0.7A 1 Vishay D1 CMSH2-60 Schottky Diode SMB 60V, 2A 1 Central Semi D2 CMDZ47L Zener Diode SOD-323 47V, 50µA 1 Central Semi L1 PF0552.223NL Inductor 12.5 x12.5 x 6.0mm 22µH, 4.8A, 35mΩ 1 Pulse Cin1 Cin2 C3225X7R1E685M Capacitor 1210 6.8µF, 25V 2 TDK Co C4532X7R1H475M Capacitor 1812 4.7µF, 50V, 3mΩ 1 TDK Cf C3216X7R1E105K Capacitor 1206 1µF, 25V 1 TDK Cinx Cox C2012X7R2A104M Capacitor 0805 100nF, 100V 2 TDK C1 VJ0805Y181KXXAT Capacitor 0805 180pF 10% 1 Vishay C2 VJ0805Y182KXXAT Capacitor 0805 1.8nF 10% 1 Vishay Css VJ0805Y222KXXAT Capacitor 0805 2.2nF 10% 1 Vishay Csns VJ0805Y102KXXAT Capacitor 0805 1nF 10% 1 Vishay Csyc VJ0805A101KXXAT Capacitor 0805 100pF 10% 1 Vishay R1 CRCW08056041F Resistor 0805 6.04kΩ 1% 1 Vishay R2 CRCW08052002F Resistor 0805 20kΩ 1% 1 Vishay Rb CRCW08053242F Resistor 0805 32.4kΩ 1% 1 Vishay Rfb1 CRCW08051241F Resistor 0805 1.24kΩ 1% 1 Vishay Rfb2 CRCW08052000F Resistor 0805 200Ω 1 Vishay Ruv1 Rpd CRCW08051002F Resistor 0805 10kΩ 1% 2 Vishay Rg Rz CRCW08050RJ Resistor 0805 0Ω 2 Vishay Rs1 CRCW0805101J Resistor 0805 100Ω 5% 1 Vishay Rs2 CRCW08056341F Resistor 0805 6.34kΩ 1% 1 Vishay Rcs ERJL14KF50M Resistor 1210 50mΩ, 0.5W 1% 1 Panasonic Rsns ERJ8BQFR20V Resistor 1206 0.2Ω, 1%, 0.33W 1 Panasonic Rt CRCW08055622F Resistor 0805 56.2kΩ 1% 1 Vishay Ruv2 CRCW08056192F Resistor 0805 61.9kΩ 1% 1 Vishay VIN, Vo/LED+ GND/LEDGND2 GND3 160-1026-03 Solder-plated Turret 0.094" 5 Cambion DIM OFF SYNC 160-1512-02 Solder-plated Turret 0.062" 3 Cambion AN-1605 LM5022 Boost LED Driver Evaluation Board SNVA229A – October 2007 – Revised May 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated PC Board Layout www.ti.com 13 PC Board Layout Figure 12. PCB Top Layer and Top Overlay SNVA229A – October 2007 – Revised May 2013 Submit Documentation Feedback AN-1605 LM5022 Boost LED Driver Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 7 PC Board Layout www.ti.com Figure 13. PCB Bottom Layer 8 AN-1605 LM5022 Boost LED Driver Evaluation Board SNVA229A – October 2007 – Revised May 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. 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