DEMO MANUAL DC1784A LT3797EUKG Triple LED Boost Controller Description DC1784A is a triple boost LED driver featuring the LT3797 triple boost LED controller. It accepts an input voltage from 2.5V to 40V (with higher transient) and drives three independent strings of up to 50V LEDs at 1A. DC1784A features independent PWM and analog dimming of each of the three LED strings. Each of the three channels has its own short-circuit protection, open LED protection, and FAULT flag output. Each or every channel can be altered to run as a different topology such as buck-boost mode, buck mode, or SEPIC depending upon the relationship between input and output voltage. Although the boost is set up to power 50V of LEDs at 1A, the maximum LED string voltage can be changed to almost 100V and the LED current can be adjusted by merely changing a few resistors and external components. DC1784A features high efficiency at 310kHz switching frequency. At high LED string voltages up to 50V and 1A of LED current, the triple LED boost controller has 93.5% efficiency. The switching frequency can be adjusted between 100kHz and 1MHz with a single resistor. All three channels run in-phase with each other and an external SYNC pin can be used to set the switching frequency and phasing, as well as to optimize PWM dimming. For low input voltage operation, down to 2.5V, the CTRL pin voltage is reduced as the input voltage drops below 10.5V, reducing LED brightness and restraining the peak switch currents in order to limit thermal rise on this PCB. The LT3797 has a unique, internal buck-boost INTVCC supply that powers the gate drivers at 7.8V, regardless of the state of the input voltage, rather than using an LDO from the input. UVLO turns the LEDs off when VIN drops below 2.5V. Internal OVLO turns off the switching when the input exceeds 41V, but OVLO can be programmed externally to a lower voltage if desired. The LT3797 can withstand transients up to 60V. DC1784A can withstand transients up to 50V with C3 > 50V rating. Small ceramic input and output capacitors are used to save space and cost. The open LED overvoltage protection uses the IC’s constant voltage regulation loop to regulate the output to approximately 55V if the LED string is opened although it may reach 59V peak during transient from running LEDs to open. The unique FBH (feedback high) pins allow the overvoltage protection of non-grounded LED driver topologies such as buck-boost mode and buck mode to be accomplished with just two resistors. Modifications can be made to DC1784A in order to convert the independent channels to higher or lower power or from LED drivers to constant voltage regulators. They can easily be changed from boost topology to SEPIC, buck mode, or buck-boost mode LED drivers. Please consult the factory or the LT3797 data sheet for details. The LT3797 data sheet gives a complete description of the device, operation and applications information. The data sheet must be read in conjunction with this demo manual for DC1784A. The LT3797EUKG is assembled in a 52-lead (7mm × 8mm) plastic QFN UKG package with a thermally enhanced ground pad. Proper board layout is essential for maximum thermal performance. See the data sheet section ‘Layout Considerations’. Design files for this circuit board are available at http://www.linear.com/demo/DC1784A L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. dc1784af 1 DEMO MANUAL DC1784A Performance Summary PARAMETER CONDITIONS VALUE (TYPICAL) Input Voltage PVIN Range Operating VIN = PVIN 2.5V to VLED (Up to 40V) Switching Frequency R1 = 47.5k 310kHz ILED CH1, CH2, CH3 R2, R3, R4 = 0.25Ω 10.5V < PVIN < VLED (40V) 1.0A Low PVIN ILED (CTRL foldback) R2, R3, R4 = 0.25Ω PVIN = 4.0V R2, R3, R4 = 0.25Ω PVIN = 6.0V R2, R3, R4 = 0.25Ω PVIN = 9.0V 280mA 525mA 890mA VLED Range CH1, CH2, CH3 R8, R9, R10 = 23.2k R14, R15, R16 = 1M PVIN < VLED < 50V Open LED Voltage CH1, CH2, CH3 R8, R9, R10 = 23.2k R14, R15, R16 = 1M 55V Typical Efficiency (100% PWM Duty Cycle) PVIN = 14V VLED = 50V and ILED = 1A CH1, CH2, CH3 93.5% PVIN Under Voltage Lockout (Falling Turn-Off) R26 = 100k and R27 = 105k 2.5V PVIN Under Voltage Lockout (Rising Turn-On) R26 = 100k and R27 = 105k 2.6V INTVCC Operating 7.5V Peak Switch Current Limit CH1, CH2, CH3 R11, R12, R13 = 0.008Ω 12.5A Quick Start Procedure DC1784A is easy to set up to evaluate the performance of the LT3797EUKG. Follow the procedure below: 1.Connect three strings of LEDs that will run with forward voltage less than 50V (at 1A), but greater than PVIN, to the LED+ and GND terminals on the PCB as shown in Figure 1. 2.Connect the EN/UVLO terminal to GND. 3.With power off, connect the input power supply to the PVIN and GND terminals. Make sure that the PVIN DC input voltage does not exceed 40V (or VLED). 4.Turn the input power supply on and make sure the voltage is between 2.5V and 40V (or VLED). 2 5.Connect the PWM1-3 input terminals to INTVCC or VREF to enable 100% brightness control when EN/UVLO is released. 6.Release the EN/UVLO-to-GND connection. 7.Observe the LED strings running at the programmed LED current. 8.To change the brightness with analog dimming, simply attach a voltage source on any or all of the CTRL terminals and set the voltage(s) between 0V and 1.5V. See data sheet for details. 9.To change brightness with PWM dimming, remove the connection from PWM1-3 to INTVCC or VREF and attach a 3.3V to 5V rectangular waveform with varying duty cycle. dc1784af DEMO MANUAL DC1784A DEmo circuit Options DC1784A can be adjusted for higher output voltage, different LED current, or different topology. The following options are for simple changes to the demonstration circuit. The data sheet gives more information regarding designing with the LT3797. For more information, see the data sheet for details or contact Linear Technology technical support. Maximum LED Voltage DC1784A is set for 55V of overvoltage protection and the maximum LED string voltage used on the standard build should be 50V. However, the output can go up to 100V, so OVP can be set at about 93V for maximum LED voltage and the maximum LED string voltage is therefore about 87V. The limits are based upon open LED overshoot and voltage and current regulation regions. If changes are made in the FB resistors for higher voltage, the MOSFET and catch diode should be switched out for higher voltage devices. See the LT3797 data sheet for details. Current or Voltage Regulation The LT3797 can be used for constant current or voltage regulation. If the load placed on the LED+ to GND terminals allows VOUT to climb high enough for VISP-FBH = 1.2V, then the voltage regulation loop of the converter takes over. In this case, the compensation for a given channel should be adjusted for proper use as a constant voltage regulator. The IC can be used as a boost or SEPIC constant voltage regulator. Output voltage can be almost as high as 100V when used as a constant voltage regulator. LED Current and Switch Current A change in LED current or input voltage may lead to higher or lower maximum switch current. R11, R12, R13 can be changed to alter the maximum switch current for different applications. 100mV/RSENSE = peak switch current. Overvoltage Protection Overvoltage protection is set with resistor pairs R8 & R14, R9 & R15, R10 & R16. The high side feedback method allows simple changes for different topologies. For buck mode and buck-boost mode, see the data sheet for details how to set the feedback resistors. Note that R35, R36, R37 are provided as optional placeholders on the demo circuit for simple feedback resistor changes for these topologies. BOOST, BUCK MODE, BUCK-BOOST MODE, SEPIC Any channel of the DC1784A can be changed to a different topology than boost. A few simple changes including feedback overvoltage protection feedback resistors, output resistor, components, and connection to input can be made. Please consult the LT3797 data sheet and the factory for details. Undervoltage and Overvoltage Lockout UVLO can be adjusted by changing the values of R26 and R27. The LT3797 has an internal 41V OVLO that protects the IC from switching at high input voltage transients. However, an additional OVLO pin can be used to set a lower OVLO using resistors R28, R31, and/or R46. LED current on DC1784A is set for 1A with 0.25Ω resistors R2, R3, R4. For a different maximum LED current, change this resistor: 250mV/RLED = ILED. dc1784af 3 DEMO MANUAL DC1784A DEmo circuit Options Figure 1. Test Procedure Setup Drawing for DC1784A 4 dc1784af DEMO MANUAL DC1784A DEmo circuit Options ILED 250:1 IL1 Figure 2. DC1784A 12VIN 100Hz PWM Dimming Waveforms at Different PWM Duty Cycles with 250:1 in Bold. ILED Waveform (500mA/Div) Is on Top (with 50V LED String) and IL1 Waveform (2A/Div) Is on the Bottom 1 OVLO (RISING) TURN-ON (FALLING) 0.6 0.4 0.2 0 0 TURN-ON (RISING) 4 UVLO (FALLING) 2 6 PVIN (V) 8 10 12 14 30 32 34 36 38 40 42 Figure 3. DC1784A CTRL LED Current Foldback at Low PVIN with UVLO Falling and Rising 100 98 96 94 92 EFFICIENCY (%) ILED (A) 0.8 90 88 86 84 82 80 0 5 10 15 20 25 30 35 40 45 PVIN (V) Figure 4. DC1784A Efficiency at Maximum ILED vs PVIN with 50V LEDs (at 1A) on All Three Channels dc1784af 5 DEMO MANUAL DC1784A Parts List ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Cap., X7R, 1µF, 50V, 10%, 0805 MURATA, GRM21BR71H105KA12L Required Circuit Components 1 1 C1 2 6 C2, C3, C4, C31, C32, C33 Cap., X7R, 4.7µF, 50V, 10%, 1210 MURATA, GRM32ER71H475KA88L 3 9 C5, C6, C7, C19, C20, C21, C25, C27, C29 Cap., X7S, 4.7µF, 100V, 20%, 1210 TDK C3225X7S2A475M 4 4 C8, C13, C14, C15 Cap., X7R, 0.1µF, 10V, 10%, 0603 AVX, 0603ZC104KAT2A 5 1 C9 Cap., X5R, 10µF, 10V, 20%, 0603 SAMSUNG CL10A106MP8NNNC 6 3 C10, C11, C12 Cap., X7R, 6800pF, 25V, 10%, 0402 AVX, 04023C682KAT2A 7 3 D1, D2, D3 DIODE, PDS360, POWERDI-5 DIODES/ZETEX, PDS360-13 8 3 L1, L2, L3 IND, 10µH, HC9-100-R COILTRONICS, HC9-100-R 9 1 L4 IND., 47µH, SD SERIES, IND-SD25 COILTRONICS, SD25-470-R 10 3 M1, M3, M5 Mosfet, N-Channel, BSC039N06NS, PWRPAK SO-8 INFINEON, BSC039N06NS 11 3 M2, M4, M6 Mosfet, P-Channel, SI7113DN, PWRPAK1212-8 VISHAY, SI7113DN-T1-GE3 12 1 R1 RES., CHIP, 47.5k, 1/16W, 1%, 0402 VISHAY, CRCW040247K5FKED 13 3 R2, R3, R4 RES., CHIP, 0.25Ω, 1W, 1%, 2010 IRC, LRC-LR2010LF-01-R250-F 14 3 R5, R6, R7 RES., CHIP, 3.9k, 1%, 0402 VISHAY, CRCW04023K90FKED 15 3 R8, R9, R10 RES., CHIP, 23.2k, 1/16W, 1%, 0402 VISHAY, CRCW040223K2FKED 16 3 R11, R12, R13 RES., CHIP, 0.008Ω, 1W, 1%, 2010 SEI, CSRF2010FT8L00 17 3 R14, R15, R16 RES., CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA 18 1 U1 IC, LT3797EUKG QFN(52)(UKG)-7mm × 8mm LINEAR TECH.CORP. LT3797EUKG#PBF Optional Electrical Components 1 0 C16, C17, C18, C22, C23, C24 CAP., OPT 0402 OPT 2 0 C26, C28, C30, C34, C35, C36 CAP., OPT 1210 OPT 3 1 C37 Cap., ALUM, 33µF, 50V, 6.3 × 7.7 PANASONIC, EEHZA1H330XP 4 3 D4, D5, D6 DIODE, ES1B, 150V/1A, SMA DIODES/ZETEX, ES1B-13-F 5 3 R17, R18, R19 RES., CHIP, 1M, 1/16W, 1%, 0402 VISHAY, CRCW04021M00FKED 6 3 R20, R21, R22 RES., CHIP, 140k, 1/16W, 1%, 0402 VISHAY, CRCW0402140KFKED 7 3 R23, R24, R25 RES., CHIP, 100k, 1/10W, 1%, 0603 VISHAY, CRCW0603100KFKEA 8 1 R26 RES., CHIP, 100k, 1/16W, 1% , 0402 VISHAY, CRCW0402100KFKED 9 1 R27 RES., CHIP, 105k, 1/16W, 1% , 0402 VISHAY, CRCW0402105KFKED 10 1 R28 RES., CHIP, 0Ω, 0402 VISHAY, CRCW04020000Z0ED 11 1 R29 RES., CHIP, 0Ω, 1/4W, 1% , 1206 VISHAY, CRCW12060000Z0EA 12 1 R30 RES., CHIP, 0Ω, 1/10W, 1%, 0603 VISHAY, CRCW06030000Z0EA 13 0 R31 to R34, R46 RES., OPT, 0402 OPT 14 0 R35 to R45 RES., OPT, 0603 OPT Hardware 1 7 E2, E10, E11, E12, E16, E17, E18 TESTPOINT, TURRET 0.094" MILLMAX, 2501-2-00-80-00-00-07-0 2 20 E4 to E9, E13 to E15, E19 to E29 TESTPOINT, TURRET 0.064" MILL-MAX, 2308-2-00-80-00-00-07-0 3 2 J1, J2 CONNECTOR, BANANA JACK KEYSTONE, 575-4 6 dc1784af J2 E2 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. GND GND GND GND INTVCC FLT3 FLT2 FLT1 CTRL3 CTRL2 CTRL1 OVLO E29 E28 E27 E26 E9 E8 E7 E6 E5 E4 E25 E24 E23 EN/UVLO GND VIN R23 100K 0603 INTVCC R29 0 1206 INTVCC VIN 2.5V - 40V R24 100K 0603 R22 140K REF R18 1M R25 100K 0603 R19 1M PVIN R21 140K R17 1M PVIN R32 OPT R31 OPT R26 100K PVIN PVIN R27 105K R28 0 PVIN R20 140K R46 OPT C37 33uF 50V C1 1uF 50V 0805 + R33 OPT C22 OPT FLT3 FLT2 FLT1 REF CTRL3 CTRL2 CTRL1 OVLO 100V 1210 1210 C25 C19 C5 4.7uF R2 0.25 M2 2010 SI7113DN 3 8 2 7 1 6 5 EN/UVLO VIN C9 10uF 10V 0603 3 2 1 7 10 9 8 52 51 50 R11 0.008 2010 BSC039N06NS M1 1210 L1 10uH D1 2 1 3 PDS360 R34 OPT R41 OPT 0603 4 C31 C2 4.7uF 50V 1210 5 6 7 8 1 2 3 PVIN C16 OPT 15 PVIN 45 16 C34 OPT 23 GATE1 4 21 SENSEP1 INTVCC 22 SENSEN1 INTVCC 46 R5 3.9K C10 6.8nF 4 C32 C3 4.7uF 50V 1210 C17 OPT 310kHz R1 47.5K 1 PDS360 D2 1210 C35 OPT OPT R42 OPT 0603 C23 R7 3.9K C12 6.8nF 100V 1210 1210 C27 C20 C6 4.7uF OUT2 C28 OPT R44 OPT 0603 C18 OPT 0603 C13 0.1uF OPT C24 0603 C14 0.1uF 4 0603 C15 0.1uF D3 1 1210 C36 OPT R13 0.008 2010 PDS360 BSC039N06NS M5 2 3 L3 10uH PVIN C33 C4 4.7uF 50V 1210 LED2+ R43 OPT 0603 R3 0.25 M4 2010 SI7113DN 8 3 2 7 6 1 5 U1 LT3797EUKG C11 6.8nF R6 3.9K R12 0.008 2010 BSC039N06NS M3 2 3 L2 10uH PVIN TG1 19 VC1 14 ISN1 5 6 7 8 1 2 3 24 28 GATE2 25 SENSEP2 PVIN VC3 40 ISP1 RT 11 LED1+ GND 53 4 OUT1 C26 OPT SS1 20 VC2 26 SENSEN2 31 ISP2 32 ISN2 33 TG2 27 PVIN SS2 44 GATE3 42 SENSEN3 43 SENSEP3 SS3 41 5 6 7 8 1 2 3 36 ISP3 37 SYNC 12 PWM3 PWM2 PWM1 SW2 BOOST SW1 FBH3 FBH2 FBH1 TG3 35 ISN3 6 5 4 47 48 49 38 30 17 SD25-470-R L4 47uH C8 0.1uF 0603 R45 OPT 0603 R37 OPT 0603 PVIN R36 OPT 0603 PVIN R35 OPT 0603 R4 0.25 M6 2010 SI7113DN 3 8 2 7 6 1 5 LED3+ PVIN 100V 1210 1210 C29 C21 C7 4.7uF C30 OPT OUT3 4 J1 R38 OPT 0603 R16 1M 0603 R15 1M 0603 R14 1M 0603 R39 OPT 0603 D6 ES1B D5 ES1B D4 ES1B R30 0 0603 R40 OPT 0603 REF 23.2K R10 23.2K R9 23.2K R8 1 1 1 2 2 2 OUT3 OUT2 OUT1 E22 E21 E20 E19 E18 E17 E16 E15 E14 E13 SYNC PWM3 PWM2 PWM1 GND GND GND OUT3 OUT2 OUT1 UP TO 50V LED 1A E12 LED3+ UP TO 50V LED 1A E11 LED2+ UP TO 50V LED 1A E10 LED1+ DEMO MANUAL DC1784A Schematic Diagram dc1784af 7 DEMO MANUAL DC1784A DEMONSTRATION BOARD IMPORTANT NOTICE Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions: This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations. If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES. The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or agency certified (FCC, UL, CE, etc.). No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive. Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and observe good laboratory practice standards. Common sense is encouraged. This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application engineer. Mailing Address: Linear Technology 1630 McCarthy Blvd. Milpitas, CA 95035 Copyright © 2004, Linear Technology Corporation 8 dc1784af Linear Technology Corporation LT 0114 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2014