LM3431EVAL

User's Guide SNVA309A – January 2008 – Revised May 2013 AN-1764 LM3431 Evaluation Board 1 Introduction The LM3431 is a combination switching boost voltage regulator and multi-channel LED current controller. The LM3431 Evaluation Board is designed to drive four parallel strings of eight series LEDs at 140mA per string from an input voltage range of 8V to 18V. The boost switcher regulates LED cathode voltage for optimum efficiency, while allowing the output voltage to vary according to the LED forward voltage. The LM3431 incorporates complete fault protection features including LED short and open protection, overcurrent protection, over-voltage and under-voltage protection, and thermal shutdown. The error detection flag can be monitored at the DLY post, which has a programmable delay time. The board includes a DIM input terminal for a selectable digital or analog dimming control signal. PWM dimming frequencies up to 1kHz at 100:1 contrast ratio and contrast ratios up to 500:1 at 200Hz are possible. The evaluation board is designed to operate at ambient temperatures up to 70°C. The complete evaluation board schematic is shown in Figure 2. Typical waveforms and performance curves are shown in Figure 3 through Figure 8. Although a wide variety of LED combinations and currents can be driven with the LM3431, the schematic must be modified to achieve optimum performance with any given array. However, for initial evaluation and demonstration, some modifications from the default settings are possible. A few of the possible variations are described below and listed in Table 2 and Table 3. LED current can be set as low as 100mA per string without significantly degrading performance; the number of strings can be reduced from 4 to 3 or 2; and the number of series LEDs can be set between 6 and 9. To design for LED arrays other than the default, and for complete device and design information, refer to the LM3431/31A/31Q/31AQ 3-Channel Constant Current LED Driver With Integrated Boost Controller (SNVS547) data sheet. 2 Before Powering Up Before powering up the LM3431 evaluation board, a few options must be selected. First, verify that the default LED current setting of 140mA is appropriate to drive the LEDs. To drive LEDs at other currents, refer to Table 2. If the required LED current is not listed, refer to the LM3431 data sheet (SNVS547), as more extensive modifications will be required. By default, the LM3431 evaluation board has channels 1-4 enabled. To drive fewer channels, first remove the sense resistor or NPN on the channel to be disabled (R10-R13 or Q2-Q5). Then refer to Table 3 and make any other required changes. This table also gives options for driving fewer LEDs per string. Finally, select the type of dimming control signal to be used. By default, R-MODE is installed, which enables digital dimming control mode. To use this mode, connect a digital PWM signal to the DIM post. The dimming signal must have a minimum high logic level of 2.3V. To enable analog dimming, remove the MODE resistor and connect an analog voltage level to the DIM post. In analog mode, the dimming duty cycle is varied by the voltage at the DIM post within a range of 0.37V to 2.5V. The default analog dimming frequency is 1kHz. To modify this frequency, change C5 as described in the datasheet. All trademarks are the property of their respective owners. SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated AN-1764 LM3431 Evaluation Board 1 Before Powering Up www.ti.com Any dimming frequency between 180Hz and 20kHz can be used in either digital or analog dimming control mode. However the default schematic is not designed for dimming frequencies above 1kHz.Once the evaluation board has been configured, connect the LED strings as shown in Figure 2. The first anode of each string connects to the VA post and the last cathode of each string connects to VC1 through VC4. LEDs can be connected either via the 8-pin header or to the terminal posts. Figure 1 shows the pinout of the header. board outline VA VA VC3 VC2 VC1 VC4 GND THM 8-pin header Figure 1. LED Connection, Top View Header Pinout Connect the input voltage supply to the VIN and GND posts. When all connections and polarities have been verified, power can be applied. When the input voltage rises above 7.7V typically, the EN pin will cross the UVLO threshold and the LM3431 will startup. EN can be pulled low (via the EN post) to shutdown the evaluation board. 2 AN-1764 LM3431 Evaluation Board SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Before Powering Up www.ti.com 8V to 18V input 700 kHz switching, 180 Hz ± 1 kHz dimming 4 strings of 8 LEDs, 140 mA per string D10 * L1 7 PH 3.1A Vin: 8V to 18V C1 C16* 1 PF RVCC * VCC + C2 10 PF R1 105k R2 20k RMODE 0: EN R16 10k DIM LG EN CS DIM C5 10 nF MODE/F REF R4 5.76k External Thermistor C10* C14 * R18 33.2k R3 51m: THM LM3431 GND AFB VCC R25 0: THM R17 95.3k VC1 D2-5 3003C VC2 VC3 VCC D6-9 1001A R9 909: COMP CFB C4 47 nF FF R5b 15.8k SNS1 RT SNS2 C7 4.7 nF SGND EP Q4 2N2222 SNS3 R21 - R23 * R10 2.2: R11 2.2: R12 2.2: + R15 1k Q3 2N2222 NDRV3 DLY Q5 2N2222 Q2 2N2222 NDRV2 SS/SH R6 34.8k C6 47 nF REFIN Op1 LMV710 NDRV1 VCC C3 4.7 PF R5a 0: VC4 R24 * SC REFIN C13 * THM PGND R8 13k C12 * R7 88.7k C11 * R19 562k C8,C9 4.7 PF ILIM LEDOFF VA Q1 Si4446 R20 * VIN LED ARRAY = 4 x 8 @140 mA D1 40V 2A R13 2.2: Q6 2N7002k R14 10k VCC LEDOFF Rrestart * C15 10 nF * = not installed Figure 2. Complete LM3431 Eval Board Schematic SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback AN-1764 LM3431 Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 3 Bill of Materials 3 www.ti.com Bill of Materials Table 1. Standard Bill of Materials Ref # Function IC1 4 Description Part Number Manufacturer Texas Instruments Boost controller and LED driver LM3431 C1 Cin 1µF 50V B ceramic GRM32RB11H105KA01 Murata C2 Cin 10µF 50V electrolytic UUD1H100MCL Nichicon C3 VCC 4.7µF 10V X7R ceramic C2012X7R1A475M TDK C4 Comp 47nF 50V X7R ceramic GRM21BR71H473KA01L3K Murata C5 MODE/F 10nF 10V COG ceramic GRM2195C1H103JA01D Murata C6 SS 47nF 50V X7R ceramic GRM21BR71H473KA01L3K Murata C7 DLY 4.7nF 50V COG ceramic GRM2165C1H472JA01D Murata C8 VA 4.7µF 50V X7R ceramic GRM32ER71H475KA88L Murata C9 VA 4.7µF 50V X7R ceramic GRM32ER71H475KA88L Murata C10 VA not installed - - C11 REFIN bypass not installed - - C12 REF bypass not installed - - C13 Comp2 not installed - - C14 THM not installed - - C15 OP1 10nF 10V COG ceramic GRM2195C1H103JA01D Murata C16 Cin not installed - - D1 power diode 2A 40V Schottky diode SS24 Vishay D2-D3 SC 600mA dual cathode diode CMPD3003C Central Semiconductor D4-D5 SC 600mA dual cathode diode CMPD3003C Central Semiconductor D6-D7 CFB 250mA dual anode diode CMPD1001A Central Semiconductor D8-D9 CFB 250mA dual anode diode CMPD1001A Central Semiconductor D10 bypass diode not installed - - L1 power coil 7µH 3.1A inductor MSS1038-702NL Coilcraft Texas Instruments Op1 ch.4 rail to rail op amp LMV710 Q1 Power FET 4A 40V N-channel MOSFET Si4446DY Vishay Q2-Q5 regulator 40V 600mA NPN transistor CXT2222A Central Semiconductor Q6 ch.4 60V 200mA N-channel MOSFET 2N7002K Vishay R1 EN uvlo set 105k 1% R2 EN uvlo set 20k R3 I sense 51mohm 0.5W 1% WSL2010R0510F Vishay R4 I limit 5.76k 1% R5a FF 0Ω R5b FF 15.8k 1% R6 RT 34.8k R7 REFIN set 88.7k 1% R8 REFIN set 13.0k 1% R9 Comp 909Ω 1% R10 - R13 LED sense 2.2Ω 1% R14 ch.4 10k R15 ch.4 1k R16 DIM 10k AN-1764 LM3431 Evaluation Board SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Optional Components www.ti.com Table 1. Standard Bill of Materials (continued) Ref # Function Description R17 THM 95.3k Part Number Manufacturer R18 AFB 33.2k R19 AFB 562k R20 HG not installed R21 - R23 - - NDRV not installed - - R24 ch.4 not installed - - R25 THM hys 0Ω Rmode MODE/F 0Ω Rrestart restart select not installed - - not installed - - RVCC 4 Optional Components Several of the components shown in the schematic are not installed and are optional. These components are typically not required, but may be useful in some applications.C10 is provided for adding additional output capacitance or for using more capacitors with smaller case sizes.C11 and C12 can be used to filter reference voltage noise. Noise at the REF_IN pin can appear as noise in the LED current. Whether these capacitors are required depends on the amount of switching noise, type of NPN used, and how much noise is tolerable in the LED current. C13 is a second compensation capacitor, which may be required if a high ESR output capacitor is used. Refer to the SNVS547 data sheet for details. D10 provides a current path from VIN to VA during startup. By bypassing the inductor, D10 prevents VA from rising above VIN at the initial power-on. In some conditions an OVP fault may occur at startup without D10 installed. R20 is a gate drive resistor for the NFET, Q1. An R20 value of up to 10Ω can be used to reduce the rise and fall time of the gate drive to reduce switching noise. To install R20, first cut the trace between the R20 pads. R21-R23 are NDRV pull-down resistors. A value of 300Ω to 1k can reduce LED current noise. These resistors are typically most effective when driving NFET current regulators. RVCC connects VCC to VIN. For 5V input applications, a 4.7Ω resistor should be installed here to pull-up VCC. For these applications, additional input capacitance at C16 may also be required. R-restart enables the automatic restart function. Auto-restart cannot be enabled when four LED channels are used. If three or fewer channels are being driven, install R-restart with 0Ω to enable the auto-restart function, which restarts the LM3431 after a fault shutdown. R-MODE selects the DIM control mode as was described previously. For lower current applications, there is a second Q1 pad which fits SOT-23 size NFETs. An external NTC thermistor can be connected either between the THM pad and SGND terminal post or via pins 7 and 8 on the 8-pin header. This thermistor is used to monitor LED temperature. With the installed R17 value, the LM3431 will enter standby when the thermistor resistance falls to 31kΩ. For example, a thermistor with a 25°C resistance of 680k and a beta constant of 4125 will yield a shutdown temperature of 110°C. R25 is a hysteresis resistor for the THM function. The default value is 0Ω which results in a restart hysteresis of 10°C. Use R25 to increase the THM hysteresis according to the data sheet description. C14 can be installed as a noise filter for the external thermistor voltage. SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated AN-1764 LM3431 Evaluation Board 5 LED String Options 5 www.ti.com LED String Options Table 2 and Table 3 give the required component changes for driving LED arrays other than the default. The values shown assume a typical LED Vf of 3.2V at 140mA. These tables are designed for simplicity and ease of modification, not optimum performance. Therefore, any of the changes listed below will result in a lower maximum contrast ratio as compared to the default LED array. For optimum performance, all component values should be reviewed. R5 in the tables refers to the sum of R5a and R5b shown on the schematic. For the best performance, R5 can be manually adjusted for the specific input voltage, dimming frequency, and LED current of each application. Table 2. LED Current Settings (nc = no change) LED current R7 R8 R5 160mA 78.7k 13k nc 130mA 100k 13k 17.4k 115mA 115k 13k 18.7k 100mA 93.1k 9.09k 20k Table 3. LED Array Options at 140mA Setting (nc = no change) 2 Strings # of LEDs R19 R3 R5 R6 6 432k 80m 24.9k 43.2k 7 499k 90m 28.7k 26.7k 8 nc 70m 30.1k 23.2k 6 432k nc 28k 43.2k 7 499k nc 24.3k nc 8 nc nc 20k nc 9 634k nc 19.1k 30.1k 6 432k nc 19.1k 43.2k 7 499k nc 16.9k nc 9 634k 40m 14.3k nc 3 Strings 4 Strings 6 AN-1764 LM3431 Evaluation Board SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Typical Evaluation Board Performance www.ti.com 6 Typical Evaluation Board Performance Unless otherwise specified, the following conditions apply: Vin = 12V, Ta = 25°C, LED array = 4 parallel strings of 8 LEDs at 140mA per string. LED part number: Nichia NFSW036BT. 700:1 VA 10V/Div MAX CONTRAST RATIO 600:1 500:1 SS/SH 1V/Div 400:1 300:1 ILED 50 mA/Div 200:1 VIN 10V/Div 100:1 0 1 ms/DIV 0 200 400 600 800 1000 1200 DIMMING FREQUENCY (Hz) Figure 3. Maximum Contrast Ratio vs. Dimming Frequency Figure 4. Power-On Startup Waveforms 100 VC1 2V/Div EFFICIENCY (%) 90 DLY 1V/Div Iout 500 mA/Div 80 70 60 50 400 Ps/DIV 8 10 12 14 16 18 INPUT VOLTAGE (V) Figure 5. Fault Delay Waveforms (one LED open) Figure 6. Efficiency vs. Input Voltage SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated AN-1764 LM3431 Evaluation Board 7 Typical Evaluation Board Performance www.ti.com VA 500 mV/Div VA 500 mV/Div ILED 5 mA/Div VC1 2V/Div VC1 1V/Div SW 10V/Div ILED 50 mA/Div 4 Ps/DIV Figure 7. Typical Dimming Waveforms (1kHz at 1% duty) 8 AN-1764 LM3431 Evaluation Board 1 Ps/DIV Figure 8. Boost Switching Waveforms SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated PCB Layout www.ti.com 7 PCB Layout Figure 9. Top Side PCB Layout Figure 10. Bottom Side PCB Layout SNVA309A – January 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated AN-1764 LM3431 Evaluation Board 9 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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