Ultr a L ow Volt age D rop LE D Con troll er for Lo w P owe r L E D s -- BC R2 0 5W Applic ation No te s Applic atio n N ote A N 256 Revision: 0.1 Date: 20 June 2011 LE D Dri ver & AF D is c retes Edition 2011-07-05 Published by Infineon Technologies AG 81726 Munich, Germany © 2011 Infineon Technologies AG All Rights Reserved. LEGAL DISCLAIMER THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. 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Life support devices or systems are intended to be implanted in the human body or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered. Application Note AN2xx256 BCR205W LED driver INTERNAL ONLY Application Note AN256 Revision History: 06 June 2011 Previous Revision: Previous_Revision_Number Page Subjects (major changes since last revision) Application Note AN2xx213, 0.1 3 / 11 6 April 2011 Application Note AN2xx56 BCR205W LED driver INTERNAL ONLY 1 Introduction 1.1 Features Wide input voltage range 1.8V – 18V Ultra low voltage overhead of only 0.2V 5mA - 80mA LED drive current with external transistor Tailored to drive LED up to 200 mW Typical 3% LED current accuracy No EMI RoHS compliant (pb-free) small SOT343 package 1.2 Figure 1 BCR205W Applications Channel letters Decorative lighting Architectural lighting Gambling & vending machines lighting Refrigerator/freezer lighting for appliances and retail use 1.3 Description The BCR205W is a simple and low cost LED controller with an Ultra Low voltage overhead providing to possibility to use the maximum amount of LEDs in series despite following constraints - LED forward voltage variation - Voltage drop along long LED chains - Tolerances in power supplies - Varying battery voltage The LED current is adjustable from 5mA to 80mA with a sense resistor. By using a digital transistor as the power stage the number of external parts can be reduced to a minimum. The small SOT-343 package allows the whole circuit to be realized on a very small PCB area. 1.4 Check List before powering up Before powering on the BCR205 demo board, please verify the following: Make sure that the input voltage supply is less than 18V. Polarity of power supply must be correct. LED anode must connect to LED+, LED cathode must connect to LEDBe sure R7 and R9 is only one of them is on board. Please avoid reconnecting the LED array between LED+ and LED- terminals without powering down first. Application Note AN2xx213, 0.1 4 / 11 6 April 2011 Application Note AN2xx56 BCR205W LED driver INTERNAL ONLY 2 PCB Design 2.1 Schematic Figure 2 Schematic of the BCR205W Demo Board Table 1 Bill-of-Materials Comment Description Designator Footprint Quantity 100nF Ceramic Capacitor C1 0805 1 option Capacitor, option, Resistor (1%) C2, C5, C6 0805 6 Input 5Pins Connector J1 EDGE_CON_TOP 1 output 2 pins Connector J2 Edge Connector -2 1 3.9 OHm 1% Resistor (1%) R1 (R2, R3, R4 optional) 0805 1 0R Resistor 0805 R7 (optional) 0805 1 1K Resistor 0805 R9 0805 1 47k Resistor 0805 R10 0805 1 BC817K-40 NPN AF Transistor T1 SOT-23 1 BCR205W LED driver U1 SOT343 1 BCR108 NPN Digital Transistor U2(optional) SOT23 1 Application Note AN2xx213, 0.1 5 / 11 6 April 2011 Application Note AN2xx56 BCR205W LED driver INTERNAL ONLY 2.2 PCB Layout Figure 3 PCB Layer information Bottom View 2.3 PCB Photograph Figure 4 Photograph of BCR205W Demo Board Application Note AN2xx213, 0.1 6 / 11 6 April 2011 Application Note AN2xx56 BCR205W LED driver INTERNAL ONLY 3 Application 3.1 Description In order to allowing user to test BCR205 LED driver performance in different power rating, we configured two type transistors, BCR108 and BC817K-40 on demo board. But user can only connect one of them at one time. In other words, can only connected R7 or R9. This demo board can driver from 5mA to 60mA LED current with different Rsense value. To increase current accuracy, four resisitors of Rsense were placed in parallel on PCB (R1, R2, R3, and R4). 3.2 LED Current vs. Input Voltage Figure 5 1 LED Current Vs. Input Voltage (with BCR108) Figure 6 3 LED Current Vs. Input Voltage (with BCR108) Application Note AN2xx213, 0.1 7 / 11 6 April 2011 Application Note AN2xx56 BCR205W LED driver INTERNAL ONLY Figure 7 1 LED Current Vs. Input Voltage (with BC817K-40) Figure 8 3 LED Current Vs. Input Voltage (with BC817K-40) Application Note AN2xx213, 0.1 8 / 11 6 April 2011 Application Note AN2xx56 BCR205W LED driver INTERNAL ONLY 3.3 LED Current vs. Rsense Figure 9 1 LED Current Vs. Rsense (with BCR108) Figure 10 1 LED Current Vs. Rsense (with BC817K-40) Application Note AN2xx213, 0.1 9 / 11 6 April 2011 Application Note AN2xx56 BCR205W LED driver INTERNAL ONLY 3.4 LED Current vs. Ambient Temperature in 3 LED Figure 11 3 LED Current Vs. Ambient temperature Application Note AN2xx213, 0.1 10 / 11 6 April 2011 w w w . i n f i n e o n . c o m Published by Infineon Technologies AG AN2xx