X RP 7 6 1 8 8-Channel Constant Current Linear LED Driver With Smart TalkTM August 2011 Rev. 2.2.0 GENERAL DESCRIPTION EVALUATION BOARD MANUAL The XRP7618 is an 8-channel, high voltage, constant-current sink LED driver capable of sinking up to 100mA current per channel. With outputs rated at 30V, the XRP7618 can control strings of multiple LEDs with better than ±1.5% channel to channel current matching. LED channel current is programmed via an external resistor within a 10mA to 100mA range. Dimming is supported up to 25kHz or through an analog signal. Featuring Exar’s Smart TalkTM technology, when combined with a boost converter, XRP7618 maximizes the overall system efficiency by dynamically reporting the minimum LED voltage necessary to maintain current regulation mode. FEATURES 8 Constant-Current Channels Adjustable up to 100mA per Channel Channel Paralleling for higher Current ±1.5% Current Matching Accuracy STANDARD CONFIGURATION The XRP7618EVB evaluation board is configured to operate under the following conditions and parameters: Input voltage range VCC: .............................. 4.2V – 5.5V Input voltage range VLED:....................................... <30V Number of LED strings: .....................................16 (2x8) LED current per string: 3 selectable pre-set levels ............. 20mA-60mA-100mA Adj. Level .......................................... 10mA to 100mA Up to 30V LED Channel Voltage Range 5V Biasing Voltage and Control Smart TalkTM Power Optimization Parallel Operations Support PWM and Analog Dimming UVLO, Open LED & Over Temperature protection 20-pin TSSOP (EP) Package EVALUATION BOARD SCHEMATICS Fig. 1: XRP7618 Evaluation Board Schematics Exar Corporation 48720 Kato Road, Fremont CA 94538, USA www.exar.com Tel. +1 510 668-7000 – Fax. +1 510 668-7001 X RP 7 6 1 8 8-Channel Constant Current Linear LED Driver With Smart TalkTM PIN ASSIGNMENT Fig. 2: XRP7618 Pin Assignment PIN DESCRIPTION Name Pin Number Description CH1 to CH8 pins Connect an LED between each pin and LED supply rail voltage (VLED). Current value is controlled by RSET. Connect unused channel(s) to GND. CHx 1, 2, 3, 4, 7, 8, 9, 10 NC 12 Not Connected PWM 11 PWM pin This must be held HIGH to enable the output drivers. It can be used for PWM dimming up to 25kHz. If not used, connect to VCC. FBX 13 FBX input pin Used in parallel configuration as an interface terminal by connecting it to FB pin of the next XRP7618. If not used, leave it unconnected. ISET 14 ISET pin Connect resistor RSET from this pin to ground to set LED channel current as per ICHANNEL=1.194x400/RSET FB 15 FB pin Samples the LED cathode voltage on each channel and outputs the lowest voltage to the step-up converter. SDB 16 SDB output pin SDB signal is synchronous with the PWM signal during PWM Dimming. SDB pin outputs low logic to the step-up converter under conditions such as shutdown or when all channels are inactive. SDBX 17 SDBX input pin Used in parallel configuration as an interface terminal by connecting it to SDB pin of the next XRP7618. If not used, connect it to GND. AGND 18 Ground pin VCC 19 Input Voltage pin Must be closely decoupled to GND pin with a 0.1μF ceramic capacitor. EN 20 Enable pin This pin must be held HIGH to enable the XRP7618. PGND 5, 6 EP Exposed Pad Ground pin Exposed Pad Connect to ground ORDERING INFORMATION Refer to XRP7618’s datasheet and/or www.exar.com for exact and up to date ordering information. © 2011 Exar Corporation 2/7 Rev. 2.2.0 X RP 7 6 1 8 8-Channel Constant Current Linear LED Driver With Smart TalkTM USING THE EVALUATION BOARD ANALOG DIMMING CONTROL Besides PWM dimming control, the LED current can be controlled continuously (from highest to lowest LED current) by raising the voltage at the bottom of RSET from 0V normally to 1V max, respectively. RSET value may be determined as POWERING UP THE XRP7618 CIRCUIT The XRP7618 Evaluation Board can be powered from a single +4.2V to +5.5V power supply. Connect with short leads directly to the “VCC” and “GND” posts on connector SV1. Note the XRP7618 will remain in “shutdown” until the “Enable” and “PWM” pins are held high or resistors R11 and R12 are fitted with 0R resistors. 1.194 where, 1.194V is a typical ISET pin voltage, VMOD is an adjustment voltage applied to the bottom side of RSET, 400 is the typical current multiplication ratio, and ILEDMAX is the required LED current per channel. LED CHANNELS CURRENT SETTING The maximum LED current per channel (ILEDMAX) can be set up to 100mA per channel through the ISET pin for each XRP7618 through an external resistor RSET. The value can be calculated by the following formula: 1.194 400 400 1.194 The XRP7618 Evaluation Board implements three switchable preset levels of current per channel (20mA, 60mA and 100mA). These levels are selected via jumpers SV4 and SV5. Additionally, resistors R4 and R19 (not populated by default) provide support for a fixed current level (jumpers SV4 and SV5 must be taken off). XRP7618EVB comes with the SV4 and SV5 jumpers set to 20mA current setting by default. Fig. 3: XRP7618 Analog Dimming Control If adjustment voltage VMOD isn’t used, RSET resistor should be connected to ground. Resistors R5 and R10 (not populated by default) support the analog dimming scheme (jumpers SV4 and SV5 must be taken off). Connect the LEDs between each channel pin and an external LED supply rail voltage (VLED). Connect unused channel(s) to GND. PARALLEL MODE OF OPERATION Multiple XRP7618s can be placed in parallel to drive over 8 strings of LEDs; unused channels should be tied to ground. XRP7618 Evaluation Board comes with two XRP7618s connected to each other through their respective FBX and SDBX pins with 0Ω resistors R13 and R14. PWM DIMMING The LED current can be adjusted by applying a PWM signal to the PWM pin. In this mode, all enabled channels are adjusted at the same time and brightness is adjusted from 1% to 100% of ILEDMAX. The supported external PWM signal frequency is 100Hz to 25kHz. © 2011 Exar Corporation 3/7 Rev. 2.2.0 X RP 7 6 1 8 8-Channel Constant Current Linear LED Driver With Smart TalkTM TYPICAL PERFORMANCE CHARACTERISTICS All data taken at VCC = 5V, RISET = 8kΩ, TA = 25°C, unless otherwise specified - Schematic and BOM from Application Information section of this datasheet. 1kHz 20 100Hz 25kHz Current per Channel (mA) 18 16 14 12 10 8 6 4 2 0 0 20 40 60 80 100 Duty cycle (%) Fig. 5: PWM Dimming: Current per Channel vs Duty Cycle Fig. 4: Current per Channel vs Temperature 59 Current per Channel (mA) Current per Channel (mA) 59 58 57 58 57 56 56 4 4.2 4.4 4.6 4.8 5 5.2 5.4 0.5 5.6 1.0 1.5 2.0 2.5 3.0 Voltage per channel (V) Input Voltage (V) Fig. 7: Current per Channel vs Voltage per Channel Fig. 6: Current per Channel vs Input Voltage 100 Current per Channel (mA) 90 80 70 60 50 40 30 20 10 0 10 20 30 40 Rset (kΩ) Fig. 9: Current per Channel vs RSET resistor Fig. 8: Maximum Output Current vs Voltage per Channel © 2011 Exar Corporation 4/7 Rev. 2.2.0 X RP 7 6 1 8 8-Channel Constant Current Linear LED Driver With Smart TalkTM EVALUATION BOARD SCHEMATICS © 2011 Exar Corporation 5/7 Rev. 2.2.0 X RP 7 6 1 8 8-Channel Constant Current Linear LED Driver With Smart TalkTM EVALUATION BOARD LAYOUT Fig. 11: Top Side Layout Fig. 10: Components Placement & Dimensions Fig. 12: Bottom Side Layout BILL OF MATERIAL Ref. Qty Manufacturer EVAL BD 1 Exar Corp. 146-6686-02 U1, U2 2 Exar Corp. XRP7618IGB-F TSSOP20 (EP) C1, C2 2 Murata Corp. GRM21BR71H104KA01L 0805 Ceramic 0.1uF, 50V, X7R R1, R6 2 Panasonic Corp. ERJ-3EKF4701V 0603 4.7KΩ Resistor, 0.1W, 1% R2, R7 2 Panasonic Corp. ERJ-3EKF8201V 0603 8.2KΩ Resistor, 0.1W, 1% R3, R8 2 Panasonic Corp. ERJ-3EKF2402V 0603 24KΩ Resistor, 0.1W, 1% R13, R14 2 Panasonic Corp. ERJ-3GEY0R00V 0603 0Ω Resistor R4, R5, R9, R10, R11, R12 6 0603 Not populated Part Number Size Component XRP7618 Evaluation Board XRP7618 SV1, SV2, SV3 3 Wurth Elektronik 61300811121 CONN.HEAD 0.1” 1x8 Pin Header SV4, SV5 2 Wurth Elektronik 61300621121 CONN.HEAD 0.1” 2x3 Pin Header SV6 1 Wurth Elektronik 61300111121 CONN.HEAD 0.1” 1x1 Pin Header © 2011 Exar Corporation 6/7 Rev. 2.2.0 X RP 7 6 1 8 8-Channel Constant Current Linear LED Driver With Smart TalkTM REVISION HISTORY Revision Date 1.0.0 08/05/2010 Initial release of document Description 1.1.0 09/22/2010 Added evaluation board picture 2.0.0 03/28/2011 Added R13 and R14 to isolate FBx and SBDx 2.1.0 07/29/2011 Modified schematics C1 and C2 to 100nF 2.2.0 08/18/2011 Added default settings information Corrected schematics for inclusion of R13 and R14 BOARD REVISION HISTORY Board Revision Date 146-6686-01 10/29/2010 Initial release of evaluation board Description 146-6686-02 03/28/2011 Added R13 and R14 to isolate FBx and SBDx FOR FURTHER ASSISTANCE Email: [email protected] Exar Technical Documentation: http://www.exar.com/TechDoc/default.aspx? EXAR CORPORATION HEADQUARTERS AND SALES OFFICES 48720 Kato Road Fremont, CA 94538 – USA Tel.: +1 (510) 668-7000 Fax: +1 (510) 668-7030 www.exar.com NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. or its in all Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. © 2011 Exar Corporation 7/7 Rev. 2.2.0