DEMO MANUAL DC1274A LTM8040 36V, 1A Step-Down Module LED Driver DESCRIPTION Demo circuit DC1274A features the LTM(R)8040 36V, 1A step-down constant current Module(R) LED driver. The demonstration circuit is designed to drive a single LED or string of LEDs at up to 1A from a wide input voltage range. The maximum LED string voltage is 13V and the minimum voltage varies depending upon the BIAS pin supply arrangement. The demonstration circuit is assembled with the BIAS pin connected to the LEDA pin. The LTM8040 runs at 500kHz switching frequency by default. DC1274A can be adjusted to raise the switching PERFORMANCE SUMMARY frequency, lower the LED current, and implement PWM dimming. The shutdown feature can be examined by connecting the shutdown terminal to ground. The LTM8040 data sheet must be read in conjunction with this demo manual prior to working on or modifying demo circuit DC1274A. Design files for this circuit board are available at http://www.linear.com/demo L, LT, LTC, LTM, Module, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. (TA = 25C) PARAMETER CONDITIONS/NOTES VALUE Input Voltage Range ILED = 1A, VLEDA = 3.3V 4V to 36V Output Current (ILED) R3 = Open 1A Switching Frequency R2 = Open 500kHz Maximum Output Voltage (VLEDA), Open LED Voltage 13V BOARD PHOTO dc1274af 1 DEMO MANUAL DC1274A QUICK START PROCEDURE DC1274A is an easy way to evaluate the LTM8040. Refer to the test procedures outlined below and Figure 1. 1. Make sure the power supply is less than 36V. With the supply OFF, connect it to the VIN and GND terminals. 2. Connect an LED or string of LEDs between the LEDA terminal and the GND terminal. For PWM dimming, the PWM dimming MOSFET must be added to the PCB and the string of LEDs must be attached between LEDA and LED- terminals. However, for simplicity, the MOSFET is not assembled on the board as shipped. 3. Turn on the input power supply and set the voltage between 4V and 36V based on the forward voltage of the LED(s) and desired output current. Please see the LTM8040 data sheet for details. 4. Tie the shutdown terminal to ground in order to turn the output off and examine the shutdown operation. Allow the IC to run by releasing the shutdown terminal connection to ground. The IC will run with the 100k pull-up resistor from the shutdown terminal to VIN. For LEDs or LED strings with a low forward voltage such as a single red LED, the BIAS terminal can be disconnected from the output (LPWR) and tied to the input (VIN). There is a small trace on the back of the PCB (layer 4) that can be cut in order to disconnect LPWR from BIAS. Please see the LTM8040 data sheet for details regarding the proper connection of the BIAS pin. dc1274af 2 DEMO MANUAL DC1274A QUICK START PROCEDURE SHDN OPTION + - A + V - + - V + A - + - Figure 1. Proper Measurement Equipment Setup 90 80 EFFICIENCY (%) 70 60 50 40 30 20 24VIN 12VIN 5VIN 10 0 0 800 200 600 400 OUTPUT CURRENT (mA) 1000 Figure 2. Efficiency with Single 3.3VF LED at 1A. LED Current is Adjusted with ADJ Voltage dc1274af 3 DEMO MANUAL DC1274A PARTS LIST ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Required Circuit Components 1 1 C1 CAP, 1210 2.2F 10% 50V X7R TDK C3225X7R1H225K 2 1 R1 RES, 0402 100k 5% 1/16W VISHAY CRCW0402100KJNED 3 1 U1 IC, MODULE LINEAR TECH. LTM8040EV Optional Demo Circuit Components 1 0 C2 CAP, 0805 OPT OPT 2 0 Q1 N-CHANNEL MOSFET, SOT-23 OPT OPT 3 0 R2, R3 RES, 0402 OPT OPT 10 E1-E10 TURRET MILL-MAX 2501-2-00-80-00-00-07-0 Hardware 1 dc1274af 4 DEMO MANUAL DC1274A SCHEMATIC DIAGRAM dc1274af 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. 5 DEMO MANUAL DC1274A 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 (c) 2004, Linear Technology Corporation dc1274af 6 Linear Technology Corporation LT 0711 * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2011