SP7616

S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement May 2009 Rev. 2.0.4 GENERAL DESCRIPTION The SP7616 is a 30V 4-Channel linear low side LED driver. It is capable of powering up to four LED strings of nine LEDs @ 60mA per string for a total of 36 LEDs with 1.5% typical current matching between channels. The desired LED current can be adjusted with an external resistor, and the precision string-tostring current matching ensures consistent color temperature across the whole display. The device also features very low dropout voltage to maximize system efficiency and avoid difficult thermal design constraints. Dimming can be achieved by feeding a PWM signal to the PWM pin, or use an analog signal to control the ISET current, this allows brightness control without unwanted color shifts. Fast LED current turn-on/off time allows up to 5 kHz PWM dimming frequencies with as low as 10% duty cycle, completely eliminating flicker. The built-in thermal protection prevents damage to the device under fault conditions. APPLICATIONS • CCFL replacement in TFT displays • Panel backlighting • Casino gaming light systems • Advertising backlighting FEATURES • Wide 4.5V to 30V operating range • 60mA LED current per channel • 1.5% channel to channel current matching • Analog Dimming control • PWM operation up to 5kHz with 10% Duty Cycle • Low dropout: 150mV @ 20mA • Built-in Over Temperature Protection • Small 2X3mm DFN package − Lead Free, RoHS Compliant TYPICAL APPLICATION DIAGRAM Fig. 1: SP7616 Application Diagram Exar Corporation 48720 Kato Road, Fremont CA 94538, USA www.exar.com Tel. +1 510 668-7000 – Fax. +1 510 668-7001 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement ABSOLUTE MAXIMUM 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. VIN ............................................................ -0.3V to 32V LED1, LED2, LED3, LED4 ............................. -0.3V to 32V ISET, PWM ................................................. -0.3V to 6.0V Storage Temperature .............................. -65°C to 150°C Power Dissipation ................................ Internally Limited Lead Temperature (Soldering, 10 sec) ................... 300°C OPERATING RATINGS Input Voltage Range VIN ................................4.5V to 30V Junction Temperature Range ....................-40°C to 100°C Thermal Resistance θJA ...................................... 59°C/W ESD Rating (HBM - Human Body Model) .................... 2kV ESD Rating (MM - Machine Model)........................... 500V Operating Junction Temperature ............ -40°C to +125°C Power Dissipation.................................Internally Limited ELECTRICAL SPECIFICATIONS Specifications with standard type are for an Operating Junction Temperature of TJ = 25°C only; limits applying over the full Operating Junction Temperature range are denoted by a “•”. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise indicated, VIN = 4.5V to 30V, CIN = 1uF, TJ = –40°C to 125°C. Parameter Operating Input Voltage Range Shutdown Supply Current Quiescent Supply Current Quiescent Supply Current Quiescent Supply Current LED Current Matching LED Current Line Regulation Line Regulation Maximum LED Current per channel LED Leakage Current Dropout Voltage Output Current Multiplication Ratio K = ILED•RSET ISET Voltage Thermal Shutdown Die Temperature Thermal Shutdown Hysteresis PWM Pin Logic LOW PWM Pin Logic HIGH PWM pin Hysteresis ISET Shutdown Threshold ISET Shutdown Threshold Hysteresis Typical PWM Maximum Dimming Frequency Typical PWM Dimming Duty Cycle Range 2.4 400 1032 1000 0.30 1075 1075 1 150 15 20 0.8 5.5 -3 Min. 4.5 30 350 1 1.5 0.5 0.1 0.05 60 2 0.45 1118 1130 V °C °C V V mV • ILED = 0mA. LED current will self recover when temperature drops below the trip point, minus thermal shut down hysteresis. Driver is disabled Driver is active If ISET is pulled above this threshold the device goes into full shutdown • Typ. Max. 30 60 500 1.5 3 3 1 0.1 Units V μA μA mA mA % %/V %/V mA μA V • • Conditions Voltage at ISET is pulled to 3V Vin 30V No LED connected, VLED pins are tied to GND. RSET=1MΩ ILED = 30mA ILED = 60mA Relative to average of all 4 channels VLED = 0.5V to 25V , VIN = 28V, RSET =50kΩ VIN = 4.5V to 25V, VLED=0.5V (Note 2) RSET = 17.4kΩ, PWM pin LOW, VLED = 1V, VIN= 5V (Note 3) ILED = 30mA, RSET=35.833kΩ, 0°C ≤ TJ ≤ 125°C 3 0.3 5 10 90 V V kHz % Applied to PWM pin. See typical performance curves. Applied to PWM pin @ 5kHz. See typical performance curves. © 2009 Exar Corporation 2/11 Rev. 2.0.4 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement Parameter Turn-on time from Shutdown Turn-off time into Shutdown Min. Typ. 100 Max. 300 20 Units μs μs Conditions VMOD from 5V to 0V, RSET = 50kΩ VMOD from 0V to 5V, RSET = 50kΩ Note 1: ILED Variations from specified by RSET value at VLED changing from 0.5 to 25V Note 2: ILED Variations from specified by RSET value at VIN changing from 4.5 to 25V Note 3: RSET = 31.6kΩ: Dropout voltage is measured as the VLED voltage where LED current drops 5% from nominal value BLOCK DIAGRAM Fig. 2: SP7616 Block Diagram © 2009 Exar Corporation 3/11 Rev. 2.0.4 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement PIN ASSIGNMENT Fig. 3: SP7616 Pin Assignment PIN DESCRIPTION Name VIN PWM ISET GND LED1-4 Pin Number 1 2 3 4 5-8 Description Input voltage for the IC. Connect a 1uF decoupling capacitor between this pin and ground. This pin must be held high to enable the output drivers. It can be used for PWM dimming up to 5 kHz. Connect resistor RSET from this pin to ground to set output current. Pulling this pin above the shutdown threshold stated in the Electrical Specifications puts the IC into shutdown mode. Ground return for LED currents and circuitry of the SP7616. Connect an LED between each pin and VIN. Current value is controlled by RSET. The current level through each pin is internally matched within 3%. Connect unused channel(s) to GND to save current consumption. ORDERING INFORMATION Part Number SP7616ER-L SP7616ER-L/TR SP7616EB Temperature Range -40°C≤TJ≤+125°C -40°C≤TJ≤+125°C SP7616 Evaluation Board Marking Package 8pin 2x3DFN 8pin 2x3DFN Packing Quantity Bulk 3K/Tape & Reel Note 1 Lead Free and/or Halogen Free Lead Free and/or Halogen Free Note 2 “YY” = Year – “WW” = Work Week – “X” = Lot Number © 2009 Exar Corporation 4/11 Rev. 2.0.4 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement TYPICAL PERFORMANCE CHARACTERISTICS All data taken at VIN = 8V, TJ = TA = 25°C, unless otherwise specified. VIN VIN ILED 20mA/DIV ILED 20mA/DIV Typical Turn on Characteristics 100 Typical Turn Maximum Input Voltage ILED PWM Duty Cycle (%) 80 PWM = 100Hz PWM = 1KHz PWM Signal 60 PWM = 5KHz VLED (Cathode Voltage) ILED 20mA/DIV 40 20 0 0 20 40 60 80 100 PWM Duty Cycle (%) PWM Duty Cycle Linearity PWM Response 1kHz 10% Duty Cycle PWM Signal PWM Signal VLED (Cathode Voltage) ILED 20mA/DIV VLED (Cathode Voltage) ILED 20mA/DIV PWM Response 1kHz 90% Duty Cycle PWM Response 1kHz 50% Duty Cycle © 2009 Exar Corporation 5/11 Rev. 2.0.4 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement PWM Signal VLED (Cathode Voltage) ILED 20mA/DIV PWM Response 5kHz 50% Duty Cycle PWM Response 5kHz 90% Duty Cycle 35 30 Shut down current in uA 25 20 15 10 5 0 5 10 15 Vin 20 25 30 PWM Response 5kHz 10% Duty Cycle 70 60 LED current in mA 50 40 30 20 10 0 0 0.2 0.4 0.6 0.8 1 Typical Shutdown Current vs Input Voltage V LED (Cathode Voltage) Typical Dropout Performance © 2009 Exar Corporation 6/11 Rev. 2.0.4 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement THEORY OF OPERATION INTRODUCTION The SP7616 is a four-channel constant current source LED driver with programmable output current level. The design consists of a regulator reference voltage source, current amplifier, and output driver. The precision reference voltage ensures good performance over voltage and temperature. The four outputs are tightly coupled allowing for excellent LED current matching. Figure 1 SETTING LED CURRENT The current in the LED strings is set by adjusting the RSET resistor connected between the ISET pin and ground. The LED current is set using the following the following equation. The RSET value may be determined from the The previous equation for VMOD = 0V. equation below shows the effect of using a VMOD in the circuit on the LED current. ILED ≈ (1V − VMOD ) Where: 1V = Typical ISET Voltage ILED = Where: K mA RSET K mA RSET K = Output Current Multiplication Ratio ILED is the desired LED current K = Output Current Multiplication Ratio ILED is the desired LED current VMOD is the adjustment voltage Note that this method of current control is not as precise as adjusting RSET. The voltage at the ISET pin is adjusted slightly during manufacturing to ensure that K, the output current multiplication ratio, is as accurate as possible. When the SP7616 was originally released at the end of 2006, the multiplication ratio and ISET voltage were specified separately. However, market feedback for better accuracy when using RSET alone prompted the change to the way the part is specified today. PWM DIMMING The LED dimming control is done through the PWM pin. The acceptable frequency range of this signal is 100Hz to 5kHz. The acceptable duty cycle range of the signal is 10% to 90% at 1KHZ. When the PWM pin is driven low, only the LED current sources are disabled while the rest of the chip is still enabled. ANALOG DIMMING CONTROL Besides digital PWM control, the LED current can be controlled continuously (from high to low LED current) by raising the voltage at the bottom of RSET, VMOD, from 0.0V to 1V maximum. This configuration is shown in figure 1 below. SHUTDOWN USING ISET PIN In normal operation, the voltage at ISET pin is around 1V. To ensure fast turn on at low duty cycle and high PWM frequency, only the output drivers are switching in PWM mode. However, the whole chip can be shutdown by pulling the voltage at ISET above 3V minimum. © 2009 Exar Corporation 7/11 Rev. 2.0.4 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement VIN CONSIDERATIONS (IMPORTANT) The VIN pin of the SP7616 (Pin 1) needs to be connected to the anode of the LED for proper operation. If these are not tied together, the part can get into a latch condition as a result of improper sequencing. A second way the part can get into a latch condition is if the input voltage falls below 1.5V but does not fall below 0.5V before the power is re-applied. In both cases, the latch condition can be “reset” by pulling the input voltage below 0.5V for >3 seconds. This latch is similar to what one might experience with a uC if a reset was not asserted after a brown out condition. At 20mA LED current and VIN = 30V additional power dissipated in the package is equal to 600mW that will increase die temperature to 59°C/W x 0.6W = 35.4C, where 59°C/W is the package thermal resistance. Assuming that all other channels are working at VLED =1.5V the die temperature will be approximately 41°C above ambient temperature and that decreases operating temperature range. Also to protect the part if too many LEDs are shorted, and the VLED voltage becomes to high, making the part dissipates too much power, the over temperature protection will shut the part off when the die temperature reaches approximately 150°C. UNUSED CHANNELS AND LED 2 CHANNEL (PIN 7) LED 2 channel should never be grounded or left unconnected it should always be used during operation. Other unused channels can be tied to the ground to save on power consumption. OVER-TEMPERATURE PROTECTION The SP7616 has over-temperature protection to prevent permanent damage to the device. When the die temperature rises above 150°C the output drivers are shut off. The output current will self recover when the temperature drops below the trip point with the preset hysteresis of 15°C. Thus a part that shut off at 150°C will not try to restart unless the die temperature is below 135°C SHORTED LEDS If all LEDs on a string are shorted, the LED cathode voltage will be VIN. It is still a working condition for this device but it significantly increases the dissipated power. © 2009 Exar Corporation 8/11 Rev. 2.0.4 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement Figure 2 Typical Application: CCFL Replacement powered from 3 Li-ion batteries. Figure 3 Using the SP7616 from a fixed source © 2009 Exar Corporation 9/11 Rev. 2.0.4 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement PACKAGE SPECIFICATION 8PIN 2X3mm DFN © 2009 Exar Corporation 10/11 Rev. 2.0.3 S P7616 High Accuracy 4-Channel Low Side LED Driver for CCFL Replacement REVISION HISTORY Revision Date Description Reformat. Increased shutdown current to 60uA. Changed specification methodology for setting LED current. Multiplier value changed to 1075 typical. Changed room and over temp limits. Dropout voltage changed to 300mV typical, 450mV maximum. Added additional information in applications “VIN Considerations” section. Updated resistor values for Maximum LED current per channel specification and current multiplication ratio. Changed PWM frequency and PWM duty cycle to typicals and referred to new curves in the typical performance graph section. 2.0.4 May 22, 2009 FOR FURTHER ASSISTANCE Email: Exar Technical Documentation: customersupport@exar.com 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. Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. or its in all © 2009 Exar Corporation 11/11 Rev. 2.0.4