XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM August 2012 Rev. 1.1.0 GENERAL DESCRIPTION APPLICATIONS The XRP7618 is an 8-channel, high voltage, constant-current sink LED driver capable of driving 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 control is supported through a standard PWM scheme up to 25kHz or through an analog signal. Featuring Exar's Smart TalkTM technology, when combined with a boost converter, the XRP7618 maximizes the overall system efficiency by dynamically reporting the minimum LED voltage necessary to maintain current regulation mode. Multiple channels can be combined to increase current driving capability per channel and multiple XRP7618s can be placed in parallel to drive over 8 strings of LEDs. An under voltage lock out, open LED and over temperature protections insure safe operations under abnormal operating conditions. LCD Backlighting Desktop, Notebook and TV Displays Industrial and Medical Displays Signage Backlighting FEATURES 8 Constant-Current Channels Adjustable up to 100mA per Channel Channel Paralleling for higher Current 1.5% Current Matching Accuracy 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 RoHS Compliant Halogen Free, 20-pin TSSOP (EP) Package The XRP7618 is available in RoHS compliant, "green"/halogen free space saving 20-pin TSSOP (EP) package. TYPICAL APPLICATION DIAGRAM Fig. 1: XRP7618 Typical Application Diagram Exar Corporation 48720 Kato Road, Fremont CA 94538, USA www.exar.com Tel. +1 510 668-7000 - Fax. +1 510 668-7001 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM ABSOLUTE MAXIMUM RATINGS OPERATING RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Input Voltage Range VCC .............................. 4.2V to 5.5V PWM Dimming Frequency .......................0.1KHz to 25KHz Current per Channel ..................................................... VCHx0.5V ........................................... 10mA to 25mA VCHx1V .............................................. 10mA to 65mA VCHx1.5V ..........................................10mA to 110mA Operating Temperature Range ................... -40C to 85C Thermal Resistance JA (TSSOP-20) ..................... 35C/W VCC, ISET, EN, FB, SDB, PWM ...................... -0.3V to 6.0V CHx .......................................................... -0.3V to 30V Junction Temperature .......................................... 150C Storage Temperature .............................. -65C to 150C Power Dissipation ................................ Internally Limited Lead Temperature (Soldering, 10 sec).................... 260C ESD Rating (HBM - Human Body Model) .................... 6kV ESD Rating (MM - Machine Model) ........................... 200V ELECTRICAL SPECIFICATIONS Specifications with standard type are for an Operating Junction Temperature of TJ = 25C only. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. Unless otherwise indicated, V CC = 5V, R ISET = 8.2k, TA= 25C. Parameter Operating Input Voltage Range VCC Min. Typ. Max. Units V Conditions 5.0 5.5 Shutdown Supply Current 0.1 1 A VEN=0V Quiescent Supply Current 0.5 1 mA No load 3.8 4.0 V Under Voltage Lockout threshold 4.2 3.6 Under Voltage Lockout Hysteresis ISET Reference Voltage Current Multiplication Ratio Maximum Output Current per Channel LED Current Matching 1.170 1.194 1.218 370 400 430 23 45 65 70 110 120 V ICHX/ISET VCHX=0.5V mA % 0.45 Current Sink Saturation Voltage VCHX=1.0V VCHX=1.5V 1.5 -1.5 Falling edge mV 200 0.8 Any 2 channels VCHX=1.0V, ICHX=60mA ICHX=20mA V 1.2 ICHX=60mA ICHX=100mA Output Current Line Regulation 2 %/V VCC=4.2V to 5.5V Output Current Load Regulation 4 % VCHX=0.5V to 2.8V 0.8 V XRP7618 is disabled V XRP7618 is active V XRP7618 is disabled V XRP7618 is active Enable Logic LOW Enable Logic HIGH 1.8 PWM Pin Logic LOW PWM Pin Logic HIGH 0.8 1.8 SDB Pin Logic LOW SDB Pin Logic HIGH Feedback Output Current Thermal Shutdown Die Temperature Thermal Shutdown Hysteresis (c) 2012 Exar Corporation 0.4 V 2.4 5 V 15 A 160 C 20 C 2/10 Rev. 1.1.0 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM BLOCK DIAGRAM Fig. 2: XRP7618 Block Diagram PIN ASSIGNMENT Fig. 3: XRP7618 Pin Assignment (c) 2012 Exar Corporation 3/10 Rev. 1.1.0 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM PIN DESCRIPTION Name Pin Number Description 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. It 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 0.1F ceramic capacitor. EN 20 Enable pin This pin must be held HIGH to enable the XRP7618. PGND 5, 6 EP Exposed Pad 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. Ground pin Exposed Pad Connect to ground ORDERING INFORMATION Part Number Temperature Range Marking Package -40CTA+85C EXAR XRP7618IGB YYWWF XXXX TSSOP-20 XRP7618IGB-F XRP7618IGBTR-F XRP7618EVB Packing Quantity Bulk 1.5K/Tape & Reel Note 1 Halogen Free RoHS Compliant Note 2 Exposed Pad XRP7618 Evaluation Board "YY" = Year - "WW" = Work Week - "X" = Lot Number, when applicable. (c) 2012 Exar Corporation 4/10 Rev. 1.1.0 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM TYPICAL PERFORMANCE CHARACTERISTICS All data taken at V CC = 5V, RISET = 8k, TA = 25C, unless otherwise specified - Schematic and BOM from Application Information section of this datasheet. 1kHz 100Hz 25kHz 20 Current per Channel (mA) 18 16 14 12 10 8 6 4 2 0 0 20 40 60 80 100 Duty cycle (%) Fig. 4: Current per Channel vs Temperature Fig. 5: PWM Dimming: Current per Channel vs Duty Cycle 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 Input Voltage (V) 1.5 2.0 2.5 3.0 Voltage per channel (V) Fig. 6: Current per Channel vs Input Voltage Fig. 7: Current per Channel vs Voltage per Channel 100 Current per Channel (mA) 90 80 70 60 50 40 30 20 10 0 10 20 30 40 Rset (k) Fig. 8: Maximum Output Current vs Voltage per Channel (c) 2012 Exar Corporation Fig. 9: Current per Channel vs RSET resistor 5/10 Rev. 1.1.0 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM THEORY OF OPERATION PWM DIMMING CONTROL The XRP7618 is an eight channel programmable constant current LED driver capable of up to 100mA per channel. A single external resistor adjusts the current for each channel over a 10mA to 100mA range with tight matching between channels. 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. Dimming is supported through a standard PWM scheme or through an analog signal. Furthermore, the XRP7618 maximizes the overall system efficiency by dynamically reporting the minimum LED voltage necessary to remain in current regulation mode when used with a boost converter. 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 Multiple XRP7618s can be placed in parallel to drive over 8 strings of LEDs; however, unused channels should be tied to ground. Built-in under voltage lock out, open LED and over temperature protections insure safe operations under abnormal operating conditions. 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 can be set up to 100mA per channel through the ISET pin. To set the reference current ISET, connect a resistor RSET between this pin and ground. The value of RSET can be calculated by the following formula: This reference current is multiplied internally with a gain (K) of 400 then mirrored on all enabled channels. This sets the maximum LED current, referred to as 100% current (ILEDMAX). The value can be calculated by the following formula: Fig. 10: XRP7618 Analog Dimming Control If adjustment voltage VMOD isn't used, RSET resistor should be connected to ground. SYSTEM POWER OPTIMIZATION The Smart Talk feature enables XRP7618 to maximize the overall system power efficiency, when used with a step-up converter, by dynamically reporting the minimum LED channel voltage needed to maintain current regulation mode. The XRP7618 samples the voltage on each channel input and reports the lowest voltage of all strings via the FB signal to the associated step up converter. or, The LED current can be reduced from 100% by PWM dimming control. If placed in shutdown through the EN pin or if all channels are inactive, the XRP7618 outputs (c) 2012 Exar Corporation 6/10 Rev. 1.1.0 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM a logic low to the converter via the SDB signal. Furthermore, the SDB signal is synchronous to the PWM signal when PWM dimming is used. CHx voltage is no longer reported. Upon reconnection of the open LED channel, current will be driven at the programmed level. OPEN LED PROTECTION PARALLEL MODE OF OPERATION The XRP7618 provides a built-in protection for open LED channel. Upon detection of an open LED channel event, the FB signal is driven low to allow the step-up converter to operate open loop which in turn raises the voltage on the remaining CHx pins. Upon reaching an internally pre-set threshold of 3V, the XRP7618 identifies the faulty channel and removes it from the control and reporting loop. At this point the FB signal resumes its normal function of reporting the lowest LED channel voltage and hence restores the proper operations of the converter. Note that the open LED channel is not disabled; however, its Multiple XRP7618s can be placed in parallel to drive over 8 strings of LEDs; however, unused channels should be tied to ground. While the initial XRP7618 is connected to the step-up converter via its FB and SDB pins, the daisy chained XRP7618s are connected to each other through the respective FBX and SDBX pins. In this configuration, the initial XRP7618 reports the lowest LED voltage and SDB signal of all the XRP7618s in parallel. Refer to figure 12. TYPICAL APPLICATION SCHEMATICS Fig. 11: Single XRP7618 Application (c) 2012 Exar Corporation 7/10 Rev. 1.1.0 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM Fig. 12: Parallel Operations with the XRP7618 Fig. 13: Single Supply Operations with the XRP7618 (c) 2012 Exar Corporation 8/10 Rev. 1.1.0 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM PACKAGE SPECIFICATION 20-PIN TSSOP (EXPOSED PAD) Unit: mm (inch) (c) 2012 Exar Corporation 9/10 Rev. 1.1.0 XRP7618 8-Channel Constant Current Linear LED Driver With Smart TalkTM REVISION HISTORY Revision Date Description 1.0.0 07/26/2011 Initial Release of datasheet 1.1.0 08/24/2012 Corrected package drawings FOR FURTHER ASSISTANCE Email: customersupport@exar.com 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. (c) 2012 Exar Corporation 10/10 Rev. 1.1.0