White LED Driver

® ISL97632 Data Sheet April 10, 2007 FN9239.2 White LED Driver with Digital Dimming The ISL97632 represents an efficient and highly integrated PWM boost LED driver that is suitable for 1.8” to 3.5” LCDs that employ 2 to 6 white LEDs for backlighting. With integrated Schottky diode, OVP, and dynamic digital dimming capability, the ISL97632 provides a simple, reliable, and flexible solution to the backlight designers. The ISL97632 features a simple single-wire digital interface that provides a 5-bit dimming control. The dimming signal adjusts the FB voltage and therefore the LED brightness in a DC manner in 32 linear steps. An EN pin can be used to provide a zero brightness setting or shutdown power saving function. The ISL97632 is available in the 8 Ld DFN (2mmx3mm) package. There are 14V, 18V, and 26V OVP options that are suitable for 3, 4, and 6 LEDs backlight applications respectively. The ISL97632 is specified for operation over the -40°C to +85°C ambient temperature at input voltage from 2.4V to 5.5V. Features • 5-Bit Digital Dimming Control • Drives up to 6 LEDs in Series • OVP (14V, 18V and 26V for 3, 4, and 6 LEDs applications) • Integrated Schottky Diode • 2.4V to 5.5V input • 86% Efficiency • 1.4MHz Switching Frequency Allows Small LC • Enable for Shutdown Function or Zero Brightness Setting • 1µA Shutdown Current • Internally Compensated • 8 Ld DFN (2mmx3mm) • Pb-Free Plus Anneal Available (RoHS Compliant) Applications • LED backlighting for - Cell phones - Smartphones - MP3 - PMP - Automotive Navigation Panel - Portable GPS Pinout ISL97632 (8 LD 2x3 TDFN) TOP VIEW GND VIN EN SDIN 1 2 3 4 8 7 6 5 LX VOUT FBSW FB Ordering Information PART NUMBER (Note) PART MARKING ELB TAPE & REEL (QTY) PACKAGE (Pb-Free) PKG. DWG.# Typical Application Circuit 10µH or 22µH VIN ISL97632IRT14Z-T 13” 8 Ld 2x3 TDFN L8.2x3A (6k pcs.) 13” 8 Ld 2x3 TDFN L8.2x3A (1k pcs.) 13” 8 Ld 2x3 TDFN L8.2x3A (6k pcs.) 13” 8 Ld 2x3 TDFN L8.2x3A (1k pcs.) 13” 8 Ld 2x3 TDFN L8.2x3A (6k pcs.) 13” 8 Ld 2x3 TDFN L8.2x3A (1k pcs.) ISL97632IRT14Z-TK ELB VIN EN SDIN FBSW FB LX VOUT ISL97632IRT18Z-T ELC ISL97632IRT18Z-TK ELC ISL97632IRT26Z-T ELD ISL97632IRT26Z-TK ELD GND NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020. 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2006-2007. All Rights Reserved All other trademarks mentioned are the property of their respective owners. ISL97632 Absolute Maximum Ratings (TA = +25°C) Input Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6V LX Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 28V FBSW Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 28V All Other Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6V Thermal Information Thermal Resistance (Typical, Note 1) θJA (°C/W) θJC (°C/W) TDFN Package (Notes 1, 2). . . . . . . . . 70 10.5 Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . +125°C Storage Temperature . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C Lead Temperature (Soldering 10s) . . . . . . . . . . . . . . . . . . . . +300°C Operating Conditions Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . .-40°C to +85°C CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed over temperature of -40°C to +85°C unless otherwise stated. Typical values are for information purposes only at TJ = TC = TA = +25°C. NOTE: 1. θJA is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. See Tech Brief TB379. 2. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside. Electrical Specifications PARAMETER VIN IIN Supply Voltage Supply Current VIN = VEN = 3V CONDITION MIN 2.4 EN = 3V, enabled, not switching EN = 0V, disabled 0.8 TYP MAX 5.5 1.5 1 1,300 90 400 ILX = 100mA VLX = 28V Serial interface setting = 15 (center) Serial interface setting = S (S = 0,1..31) Serial interface setting = 0 90 95 9.8 + 5.68 x S 9.8 1 10 IDIODE = 100mA, TA = +25°C ISL97632IRT14Z ISL97632IRT18Z ISL97632IRT26Z 600 14 18 26 28 0.6 1.5 SDIN = low SDIN = low SDIN = low SDIN = high 15 90 215 3 45 120 850 1,450 95 470 900 1 100 1,600 UNIT V mA μA kHz % mA mΩ μA mV mV mV μA Ω mV V V V V V μs μs μs μs DESCRIPTION Fsw DMAX ILIM RSW(LX) ILEAK VFB Switching Frequency Maximum Duty Cycle LX Current LX Switch ON-Resistance LX Switch Leakage Current Feedback Voltage IFB RSW(FBSW) VDIODE OVP FB Pin Bias Current FBSW Switch ON-Resistance Schottky Diode Forward Voltage Overvoltage Protection VFB = 95mV VIL VIH tLOGIC1 tLOGIC0 tLOGIC-LOAD tLOGIC-HIGH Logic Low Voltage Logic High Voltage Timing Range for Logic 1 Timing Range for Logic 0 Timing Range for Load Minimum Valid SDIN High Time 2 FN9239.2 April 10, 2007 ISL97632 Block Diagram VIN (2.4V to 5.5V) CIN VIN EN L LX 1.4MHZ OSCILLATOR AND RAMP GENERATOR ISL97632 VOUT COUT PWM COMPARATOR PWM LOGIC CONTROLLER FET DRIVER 2 to 6 LEDs CURRENT SENSE GND FBSW EN GM AMP COMPENSATION SDIN GM AMPLIFIER FB 10 - 186mV BANDGAP REFERENCE GENERATOR RSET SERIAL INTERFACE Pin Descriptions PIN NUMBER 1 2 3 4 5 6 7 8 PIN NAME GND VIN EN SDIN FB FBSW VOUT LX Ground Pin. Connect to local ground. Input Supply Pin. Connect to the input supply voltage, the inductor and the input supply decoupling capacitor. Enable Pin. Connect to enable signal to turn-on or off the device. Active High. Single-Wire XSD Digital Interface. Feedback Pin. Connect to the cathode of bottom LED and the sense resistor. Optional FB Disconnect Switch. Output Pin. Connect to the anode of the top LED and the output filter capacitor. Switching Pin. Connect to inductor. DESCRIPTION 3 FN9239.2 April 10, 2007 ISL97632 Single-Wire Serial Interface 30µs 100µs 220µs '1' '0' '1' '0' '0' 'LOAD' 0 200 400 600 800 1000 1200 µs FIGURE 1. SINGLE-WIRE XSD INTERFACE The ISL97632 uses a simple single-wire serial interface for programming the output brightness of the LEDs. A 5-bit interface is used to give a total of 32 levels of output brightness. The interface uses a normally high connection for use with open-drain driving schemes and Intersil’s proprietary XSD bus. When held low for between 15µs and 45µs, the interface registers a logic 1. When held low for between 90µs and 120µs the interface registers a logic 0. When held low for greater that 215µs, the interface loads the last 5 bits into the brightness control register and updates the brightness level. The required minimum high time is 3µs. This simple single-wire programming is summarized as follow: • Logic 0 = Negative pulse >90µs and <120µs • Logic 1 = Negative pulse >15µs and <45µs • Load = Negative pulse >215µs Figure 1 shows an example of programming a binary code of 10100 and load it in to the device serial register. The serial interface is automatically reset to 0 when the device is disabled, or enters UVLO. Therefore, when the part is enabled, the output brightness is automatically set to the minimum level. 4 FN9239.2 April 10, 2007 ISL97632 Typical Performace Curves 90 4.2V IN 4 LEDs OUT (15µH) 85 80 EFFICIENCY (%) 75 70 65 60 55 50 0 5 10 15 20 25 30 35 40 45 IOUT (mA) 3.6V IN 4 LEDs OUT (22µH) 0 - 0.2 0 1 2 VIN (V) 3 4 5 3.6V IN 4 LEDs OUT (10µH) 3.6V IN 4 LEDs OUT (15µH) 4.2V IN 4 LEDs OUT (10µH) 4.2V IN 4 LEDs OUT (22µH) Iq (mA) IO (mA) 5 10 15 VOUT (V) 20 25 30 0.6 0.4 0.2 0.8 1 FIGURE 2. EFFICIENCY vs LED CURRENT FIGURE 3. QUIESCENT CURRENT vs VIN (ENAB = HI) 20.08 19.76 19.74 20.04 19.72 IO (mA) 20.00 19.70 19.68 19.66 19.64 19.92 0 19.62 2.5 19.96 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 FIGURE 4. LOAD REGULATION (VIN = 4V) FIGURE 5. LINE REGULATION 40 35 30 IO (mA) 25 20 15 10 5 0 0 5 10 15 20 25 30 35 CODE = DECIMAL RSET = 4.7Ω FIGURE 6. ILED vs PROGRAMMING CODES 5 FN9239.2 April 10, 2007 ISL97632 Detailed Description The ISL97632 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. There are three OVP models for driving 3, 4, and 6 LEDs and their OVP thresholds are set at 14V, 18V, and 26V respectively. The ISL97632 operates from an input voltage of 2.4V to 5.5V and ambient temperature from -40°C to +85°C. The switching frequency is around 1.45MHz and allows the driver circuit to employ small LC components. The forward current of the LED is set using the RSET resistor. In the steady state mode, the LED current is given by Equation 1: V FB ( S ) 9.8mV + 5.68mV × S I LED ( S ) = ------------------- = ------------------------------------------------------R SET R SET (EQ. 1) resume previous setting, the device needs to be reprogrammed. Output Disconnect The ISL97632 features a FBSW feedback disconnect switch that can be used in between the LED and Rset for an optional short-circuit protection. For example, the user may build an external short circuit detection to monitor the VOUT. If the VOUT goes low due to