DEMO MANUAL DC780A LT1618 Constant-Current 1.4MHz White LED Driver DESCRIPTION Demonstration circuit 780A is a constant-current 1.4MHz white LED driver featuring the LT®1618. The board is optimized for 3.5V LED forward voltage output at 320mA load current and a single lithium-ion input voltage range of 3.3V to 4.2V. With its high frequency, constant-current amplifier, internal power switch, low quiescent current, 1.4MHz switching frequency and thermally enhanced package, the LT1618 is a very versatile and powerful IC for driving 1W LEDs (such as a Luxeon LED, not installed) that require either step-up and step-down capability from lithium-ion supplies or step-up capability from 2-cell 1.8V to 3.0V supplies used in very compact handheld solutions. The LT1618 1.4MHz switching frequency allows all of the components to be small, surface mount devices. The current-mode control topology creates fast transient response and good loop stability with a minimum number of external components. The constant-current amplifier provides constant-current sensing without the need of an PERFORMANCE SUMMARY PARAMETER external operational amplifier as used in other constantcurrent LED driver DC/DC converters. The ON/OFF pushbutton is used to manually turn on the LED. The BRIGHTNESS pushbutton is used to pulse the LED in a brighter, higher current mode when the LED is ON. The IADJ terminal can be used to program the LED current. The VLED+ and VLED– terminals can be used to monitor the LED forward voltage. The LT1618 data sheet gives a complete description of the part including operation and applications information. The data sheet must be read in conjunction with this Quick Start Guide for demonstration circuit 780A. Design files for this circuit board are available at http://www.linear.com/demo 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. (TA = 25°C) CONDITION Input Voltage Range VALUE 3.3V to 4.2V LED OFF Input Current VIN = 3.6V, LED OFF 4μA VLED VIN = 3.3V to 4.2V, BRIGHTNESS OFF, Luxeon LED 3.2V VIN = 3.3V to 4.2V, BRIGHTNESS ON, Luxeon LED 3.4V VIN = 3.3V to 4.2V, BRIGHTNESS OFF, Luxeon LED 250mA VIN = 3.3V to 4.2V, BRIGHTNESS ON, Luxeon LED 500mA LED Ripple Current VIN = 3.6V 35mAP–P Switching Frequency VIN = 3.3V to 4.2V 1.4MHz Efficiency VIN = 3.6V, BRIGHTNESS OFF, Luxeon LED 71% VIN = 3.6V, BRIGHTNESS ON, Luxeon LED 65% ILED dc780af 1 DEMO MANUAL DC780A QUICK START PROCEDURE Demonstration circuit 780A is easy to set up to evaluate the performance of the LT1618. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE: Make sure that the input voltage does not exceed 4.2V. NOTE: The IADJ (current adjust) function is optional and its terminal can be left floating (disconnected) if not being used. 1. Connect the power supply (with power off) LED and meters as shown in Figure 1. NOTE: If the LED is not on, make sure that the current limit on the supply is not set too low. 3. While depressing the ON/OFF button, pulse the BRIGHTNESS button (pulse only for less than one second intervals) and observe the LED brightness increasing in a flash-type manner. 4. Once the operation of the LED is established, adjust the supply within the operating range and observe the LED brightness, LED forward voltage, efficiency and other parameters. 2. After all connections are made, turn on input power and verify that the LED turns on when the ON/OFF button is depressed. Figure 1. Proper Measurement Equipment Setup dc780af 2 DEMO MANUAL DC780A OPTIONAL FUNCTIONS IADJ (CURRENT ADJUST) TIMER-CONTROLLED ON/OFF AND FLASH The ON/OFF and BRIGHTNESS pushbuttons are used to manually demonstrate how bright a LED is with 250mA and 500mA of LED current. For some applications, adjustable brightness at levels other than the two constant-current settings mentioned above is desirable. The LT1618 has a SHDN pin that is used to control the LED ON/OFF function on demonstration circuit 780A. The ON/OFF momentary pushbutton is manually controlled. An external signal can be used to turn the LED ON and OFF by replacing the ON/OFF pushbutton and R6 pulldown resistor with an external signal. To control a pulse of extra-bright light (maximum current) another external signal can drive a low impedance MOSFET replacing the BRIGHTNESS momentary pushbutton. This is sometimes referred to as flash mode and torch mode (lower current, brightness OFF). Please see Figure 3 for details. Please see the LT1618 data sheet for more information on the IADJ pin function. VIN ON/OFF VIN SW LT1618 1M SHDN ISP ISN 5.1k 0.1μF 1.65V PWM GND VIN LED ON PULSE FB IADJ NC SW LT1618 SHDN VC ISP ISN DC780A F02 500mA 250mA Figure 2. Implementation of the IADJ Function Using a 1.65V 10kHz PWM Signal and an RC Filter for LED Dimming. FB IADJ 2.2M GND NC VC FLASH PULSE DC780A F03 Figure 3. Implementation of the Flash and Torch Modes Using External Timing Devices. Flash Mode is 500mA Pulsed LED Current and Torch Mode is 250mA. 100 90 EFFICIENCY (%) 80 BRIGHTNESS OFF 70 60 BRIGHTNESS ON 50 40 30 20 10 0 3.3 3.6 3.9 4.2 VIN (V) DC780A F04 Figure 4. DC780A Typical Efficiency (TA = 25°C) LED Used = L × HL – BW02 dc780af 3 DEMO MANUAL DC780A OPTIONAL FUNCTIONS C4 MEAN 48.12mV 400ns/DIV DC780A F05 Figure 5. DC780A LED Has Constant Current with Low Ripple. LED ON, BRIGHTNESS OFF. CH4 is LED Current 50mA/DIV C4 MEAN 47.74mV 400ns/DIV DC780A F06 Figure 6. DC780A LED Has Constant Current with Low Ripple. LED ON, BRIGHTNESS ON. CH4 is LED Current 100mA/DIV dc780af 4 DEMO MANUAL DC780A OPTIONAL FUNCTIONS 2V 10mVΩ 100μs/DIV DC780A F07 Figure 7. DC780A LED Turn-On Transient is Quick and without Overshoot. BRIGHTNESS OFF. CH1 is LED Forward Voltage, CH4 is LED Current 50mA/DIV 2V 10mVΩ 100μs/DIV DC780A F08 Figure 8. DC780A LED Turn-On Transient is Quick and without Overshoot. BRIGHTNESS ON. CH1 is LED Forward Voltage, CH4 is LED Current 100mA/DIV dc780af 5 DEMO MANUAL DC780A PARTS LIST ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Required Circuit Components 1 1 C1 CAP, X5R 1μF 10V 20% 0603 TAIYO YUDEN LMK107BJ105MA 2 1 C2 CAP, X5R 4.7μF 10V 20% 0805 AVX 0805ZD475MAT 3 1 C3 CAP, X5R 0.1μF 10V 10% 0402 AVX 0402ZD104KAT 5 1 D2 DIODE, SCHOTTKY BARRIER PHILIPS PMEG2010EA 7 1 L1 INDUCTOR, 10μH COOPER SD25-100 8 1 R1 RES, 124k 1% 1/16W 0402 AAC CR05-1243FM 9 1 R2 RES, 866k 1% 1/16W 0402 AAC CR05-8663FM 10 1 R3 RES, 0.10Ω 1% 1/16W 0603 AAC CRL16-R100FOM 11 1 R4 RES, 2.2MΩ 5% 1/16W 0402 AAC CR05-225JM 12 1 R5 RES, 1MΩ 5% 1/16W 0402 AAC CR05-105JM 15 1 U1 IC, LT1618EDD LINEAR TECHNOLOGY LT1618EDD Additional Demo Board Circuit Components 1 0 D1 LED, OPT OPT 13 0 R6 RES, 0603 OPT OPT Hardware/Components (For Demo Board Only) 14 2 SW1, SW2 SWITCH, MOMENTARY, PUSH BUTTON PANASONIC EVQPJS05K 6 5 E1 TO E5 TURRETS MILL-MAX-2501-2 dc780af 6 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. A B C D 4 E1 E4 5 IADJ GND E3 E2 3.3V-4.2V VIN VLED- C1 1uF 6.3V SW1 4 *500mA PULSE ONLY 250mA/500mA BRIGHTNESS 1M R5 OFF / ON 2 SW2 1 5 OPT U1 2 2.2M R4 4 9 R6 LT1618EDD OPT 1 D1 8 Iadj SHDN Vin SD25 L1 10uF 3 1 2 3 Thursday, August 11, 2011 DESIGNER ENGINEER APPROVED CHECKED MEI APPROVALS DRAWN 6 3 0.1uF C3 Fb Isn Isp SW CONTRACT NO. GND 5 7 SW Vc 10 This circuit is proprietary to Linear Technology and supplied for use with Linear Technology parts. Customer Notice:Linear Technology has made a best effort to design a circuit that meets customer-supplied specifications; however, it remains the customers responsibility to verify proper and reliable operation in the actual application, Component substitution and printed circuit board layout may significantly affect circuit performance or reliability. Contact Linear Applications Engineering for assistance. 02/18/04 DATE 1 TECHNOLOGY 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 SCALE: DWG NO 2 FILENAME: 780A-2.1.DSN SIZE CAGE CODE SHEET DC780A 1 1 OF 1 2.1 REV WALKER B. APPROVED SCH, LT1618EDD, CONSTANT-CURRENT 1.4MHz WHITE LED DRIVER R1 124k R2 866k 4.7uF 0.10 D2 C2 R3 VLED+ D1 BECOMES OPTIONAL 2.1 E5 PROTO 08/11/11 DATE 03/16/04 DESCRIPTION 1 2 REVISION HISTORY REV PMEG2010EA 2 TITLE ECO 2 A B C D DEMO MANUAL DC780A SCHEMATIC DIAGRAM dc780af 7 DEMO MANUAL DC780A 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 dc780af 8 Linear Technology Corporation LT 0911 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2011