LT3744 LINER

Document overview

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Technical content

Description

Demonstration circuit 2339A is a high current synchronous step-down LED driver featuring the LT®3744. The unique drive stage used on the LT3744 allows the anodes of three LEDs to be connected together for better heat sinking. This connection will work in both the step-down configuration and the inverting buck-boost configuration. The pros and cons of each configuration can be found in the data sheet. This demonstration circuit 2339A is for customers to test the step-down configuration only. The inverting buck-boost configuration is shown in a separate demonstration circuit. The input of the demo board is up to 36V. The components are optimized for the efficiency, thermal and PWM dim- ming for a 12V input. Each of the three outputs is up to , 20A with a 6.05V maximum output voltage limit. The PWM1, PWM2 and PWM3 pins are set to low by default. A DC or PWM signal is required to connect to at least one of the PWM pins to enable the circuit. At any giving time, output current only passes through one LED determined by settings of PWM pins. The CTRL1, CTRL2 and CTRL3 pins can be adjusted to provide accurate analog dimming down to 20:1 ratio. The minimal input voltage for the LT3744 to operate is 3.3V. However, to maintain the output current regulation in a step down regulator, the minimum input voltage is determined by the LED voltage and the maximum duty cycle. For a 5V output, the demo board minimum input voltage will be around 5.5V at room temperature. The load to be used with this demo board is high current LEDs or laser diodes. Smaller LEDs may not be able to handle the high current, even for a short period of time. It is necessary to mount the LED load on a proper heat sink. A fan may become necessary to avoid exceeding LED’s maximum temperate rating. L, L T , L TC, L TM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. The typical efficiency of the demo board is 93.5% from a 12V input to 5V, 20A load. The lower the input voltage, the higher the efficiency tends to be for a given load. At output power level of 100W, even one percent of efficiency improvement is a big advantage in minimizing temperature rise. If an efficiency measurement is needed in an applica- tion, the output voltage must be measured at the output capacitors instead of the LED load. This prevents cable loss from being counted as a loss of the board. The demo circuit DC2399A achieves fast current rise time from 0A to 20A in 5µs. To see the real rise time, connecting wires between the LED and the board should be as short as possible to minimize the wire inductance and resistance. It is recommended to measure the voltage across R32 with a short 50Ω coax cable directly into a BNC connector on the oscilloscope. The current can be calculated from the measured voltage. Figure 1 shows the current rise time. A current probe adds more delays to the rise time so using a current probe is not recommended unless rise time is not a concern. The LT3744 data sheet gives a complete description of the part, operation and application information. The data sheet must be read in conjunction with this quick start guide for demo circuit 2339A. Design files for this circuit board are available at http://www.linear.com/demo/DC2339A

Demonstration circuit 2339A is easy to set up to evalu- ate the performance of the LT3744. Refer to Figure 2 for proper measurement equipment setup and follow the procedure below: 1. With power off, connect the input power supply to PVIN and GND. Note: make sure PVIN is below 36V. Con- nect a DC supply or a PW M signal to PWM1, PWM2 and/or PWM3. 2. With power off, connect the LED load to V LED+ and proper LED1–, LED2–, LED3– according to the setting of the PWM pins. 3. Turn on the power at the input. Turn on PWM1, PWM2 and/or PWM3. 4. Carefully evaluate other design parameters as needed. performance summary Specifications are at TA = 25°C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS PVIN Input Supply Voltage VLED+ = 5V 5.5 36 V VLED+ Maximum Output Voltage 6.05 V IOUT Output Current CTRL1, CTRL2, CTRL3 = 1.5V 19 20 21 A fSW Switching Frequency 380 425 470 kHz EFF Efficiency at DC VIN = 12V, IOUT = 20A, VOUT = 5V 93.5 % Figure 1. DC2339A Current Rise Time. VIN = 12V, LED Voltage = 4.2V when ON. Total LED Current = 20A

Figure 2. Proper Measurement Equipment Setup

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Required Circuit Components 1 6 C1, C2, C24, C25, C30, C31 CAP., X7R, 10µF, 50V, 10%, 1210 MURATA, GRM32ER71H106KA12L 2 2 C4, C5 CAP., ALUM., ELECT., 56µF, 50V SUN ELECT., 50HVT 56M 3 1 C6 CAP., X7R, 0.22µF, 25V, 10% 0603 MURATA, GRM188R71E224KA88D 4 1 C7 CAP., X7R, 1µF, 50V, 10% 0805 AVX, 08055C105KAT2A 5 1 C8 CAP., X7R, 22µF, 6.3V, 10% 0805 AVX, 08056D226KAT2A 6 1 C9 CAP., X5R, 47µF, 10V, 10% 1206 MURATA, GRM31CR61A476KE15L 7 3 C11, C12, C16 CAP., POSCAP, 470µF, 6.3V, D4D PANASONIC, 6TPF470MAH 8 1 C14 CAP., X5R, 2.2µF, 25V, 10% 0603 MURATA, GRM188R61E225KA12D 9 4 C18, C21, C22, C23 CAP., X7R, 10nF, 25V, 10% 0603 AVX, 06033C103KAT2A 10 5 C26-C29, C19 CAP., X7R, 1nF, 25V, 10% 0603 AVX, 06033C102KAT2A 11 1 D1 SCHOTTKY RECTIFIER, 40V, SOD523 NXP, PMEG4002EB 12 2 D3, D4 DIODE, BAT54A SOT23 DIODES INC., BAT54A-7-F 13 1 L1 INDUCTOR, 0.82µH Würth Elektronik, 744355182 14 2 Q1, Q2 N-CH., 40-V, PG-TDSON-8 INFINEON, BSC035N04LS G 15 2 Q3, Q5 N-CH., 40-V, PG-TDSON-8 INFINEON, BSC026N04LS 16 3 Q4, Q6, Q7 N-CH., 12-V, PowerPAK SO-8 VISHAY, Si7234DP-T1-GE3 17 3 Q8-Q10 N-CH., 40-V, PG-TDSON-8 FL INFINEON, BSC010N04LS 6 R1, R4, R12, R13, R33, R36 RES., CHIP., 0Ω, 1/10W, 0603 VISHAY, CRC06030000Z0EA 19 10 R3, R6-R8, R10, R20-R23, R25 RES., CHIP., 100K, 1/10W, 1% 0603 VISHAY, CRCW0603100KFKEA 20 2 R5, R32 RES., CHIP., 0.003Ω, 3W, 1%, KRL6432 SUSUMU, KRL6432E-M-R003-F 21 1 R14 RES., CHIP., 4.02K, 1/10W, 1% 0603 VISHAY, CRCW06034K02FKEA 22 1 R16 RES., CHIP., 82.5K, 1/10W, 1% 0603 VISHAY, CRCW060382K5FKEA 23 3 R17, R18, R19 RES., CHIP., 309K, 1/10W, 1% 0603 VISHAY, CRCW0603309KFKEA 24 1 R27 RES., CHIP., 1k, 1/10W, 1% 0603 VISHAY, CRCW06031K00FKEA 25 3 R29, R30, R31 RES., CHIP., 25.5k, 1/10W, 1% 0603 VISHAY, CRCW060325K5FKEA 26 1 U1 I.C. LT3744EUHE 36PIN, UHE LINEAR TECH., LT3744EUHE#PBF Additional Demo Board Circuit Components 1 0 C10, C13, C15(OPT ) CAP., D4D 2 0 C17 (OPT ) CAP., 0603 3 0 D2(OPT ) DIODE, DI123 4 0 R2, R9(OPT ) RES., CHIP., 0603 Hardware: For Demo Board Only 1 16 E1-E16 TESTPOINT, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0 2 8 J1-J8 JACK BANANA KEYSTONE, 575-4 3 4 STAND-OFF STAND-OFF, NYLON, 0.25" (SNAP ON) KEYSTONE, 8831

Information furnished by Linear Technology Corporation is believed to be accurate and reliable. tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. Figure 3. F. DC2339A Demo Circuit Schematic

DEMO MANUAL DC2339A Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear .com  LINEAR TECHNOLOGY CORPORATION 2015 LT 0215 • PRINTED IN USA DEMONSTRATION BOARD IMPORTANT NOTICE Linear Technology Corporation (LT C) 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 ONL Y and is not provided by LT C 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 P ARTY 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 LT C 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. LT C assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. LT C 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 LT C applica- tion engineer . Mailing Address: Linear Technology 1630 McCarthy Blvd. Milpitas, CA 95035 Copyright © 2004, Linear Technology Corporation