White LED Driver

® ISL97634 Data Sheet April 10, 2007 FN6264.2 White LED Driver with Wide PWM Dimming Range The ISL97634 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 wide range of PWM dimming capability, the ISL97634 provides a simple, reliable, and flexible solution to the backlight designers. The ISL97634 features a wide range of PWM dimming control capability. It allows dimming frequency as low as DC to 32kHz beyond audible spectrum. The ISL97634 also features a feedback disconnect switch to prevent the output from being modulated by the PWM dimming signal that minimizes system disturbance. The ISL97634 is available in the 8 Ld TDFN (2mmx3mm) package. There are 14V, 18V, and 26V OVP options that are suitable for 3 LEDS, 4 LEDs, and 6 LEDs backlight applications respectively. The ISL97634 is specified for operation over the -40°C to +85°C ambient temperature at input voltage from 2.4V to 5.5V. Features • Drives Up to 6 LEDs in Series • OVP (14V, 18V, and 26V for 3, 4 and 6 LEDs Applications) • PWM Dimming Control From DC to 32kHz • Output Disconnect Switch • Integrated Schottky Diode • 2.4V to 5.5V Input • 85% Efficiency • 1.4MHz Switching Frequency Allows Small LC • 1µA Shutdown Current • Internally Compensated • 8 Ld TDFN (2mmx3mm) • Pb-Free Plus Anneal Available (RoHS Compliant) Applications • LED Backlighting for: - Cell phones - Smartphones - MP3 - PMP - Automotive Navigation Panel - Portable GPS Pinout ISL97634 (8 LD TDFN) TOP VIEW GND VIN PWM/EN NC 1 2 3 4 8 7 6 5 LX VOUT FBSW FB Ordering Information PART NUMBER (Note) ISL97634IRT14Z-T PART MARKING ELE TAPE & REEL (QTY) PACKAGE (Pb-free) PKG. DWG. # Typical Application Circuit 10µH or 22µH VIN 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.) ISL97634IRT14Z-TK ELE ISL97634IRT18Z-T ELF VIN PWM/EN NC LX ISL97634IRT18Z-TK ELF VOUT ISL97634IRT26Z-T FBSW FB ELG ISL97634IRT26Z-TK ELG 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. ISL97634 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 θJA (°C/W) θJC (°C/W) TDFN Package (Notes 1, 2). . . . . . . . . 77 12 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. Typ 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 = VPWM/EN = 3V CONDITION MIN 2.4 PWM/EN = 3V, enabled, not switching PWM/EN = 0V, disabled 0.8 TYP MAX 5.5 1.5 1 1,300 90 400 ILX = 100mA VLX = 28V 90 VFB = 95mV 10 IDIODE = 100mA, TA = +25°C ISL97634IRT14Z ISL97634IRT18Z ISL97634IRT26Z 600 14 18 26 28 0.6 1.5 850 1,450 95 470 900 0.01 95 1 100 1 1,600 UNIT V mA μA kHz % mA mΩ μA mV μA Ω mV V V V V V DESCRIPTION fSW DMAX ILIM RSW(LX) ILEAK VFB IFB RSW(FBSW) VDIODE OVP Switching Frequency Maximum Switching Duty Cycle LX Current LX Switch ON-Resistance LX Switch Leakage Current Feedback Voltage FB Pin Bias Current FBSW Switch ON-Resistance Schottky Diode Forward Voltage Overvoltage Protection VIL VIH Logic Low Voltage of PWM/EN Logic High Voltage of PWM/EN 2 FN6264.2 April 10, 2007 ISL97634 Block Diagram VIN (2.4V to 5.5V) CIN VIN PWM/EN L LX 1.4MHZ OSCILLATOR AND RAMP GENERATOR ISL97634 VOUT COUT PWM COMPARATOR PWM LOGIC CONTROLLER FET DRIVER 2 LEDs to 6 LEDS CURRENT SENSE GND FBSW PWM/EN GM AMP COMPENSATION GM AMPLIFIER FB 95mV BANDGAP REFERENCE GENERATOR RSET Pin Description PIN NUMBER 1 2 3 4 5 6 7 8 PIN NAME GND VIN PWM/EN NC 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. PWM or Enable Pin. Connect external PWM signal allows pulse width modulation current operation. Enable signal allows peak current operation or disable signal shuts down the device. No Connect Feedback Pin. Connect the sense resistor between FB and ground. The cathode of bottom LED can also be connected at this pin if the output current is not to be PWMed. FB Disconnect Switch. Connect to the cathode of the bottom LED if the output current to be PWMed. Output Pin. Connect to the anode of the top LED and the output filter capacitor. Switching Pin. Connect to inductor. DESCRIPTION 3 FN6264.2 April 10, 2007 ISL97634 Typical Performance Curves 90 85 80 EFFICIENCY (%) 75 3 LEDs, 10µH 70 65 60 55 50 3 LEDs, 22µH 6 LEDs, 22µH ILED_peak = 25mA VIN = 4V RSET = 4Ω fPWM = 1kHz 0 20 40 60 80 PWM DUTY CYCLE (%) 100 6 LEDs, 10µH 4 LEDs, 10µH Iq (mA) 0.6 1.0 0.8 0.4 0.2 0.0 -0.2 0 1 2 3 VIN (V) 4 5 6 FIGURE 1. EFFICIENCY vs PWM DUTY CYCLE FIGURE 2. QUIESCENT CURRENT vs VIN (PWM/EN = HI) 20.08 19.76 19.74 20.04 19.72 IO (mA) IO (mA) 19.70 19.68 19.66 19.64 19.92 19.62 20.00 19.96 0 5 10 15 VOUT (V) 20 25 30 2.5 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 FIGURE 3. LOAD REGULATION (VIN = 4V) FIGURE 4. LINE REGULATION 100 90 80 FB VOLTAGE (mV) 70 60 50 40 PWM/EN 30 20 10 0 0 20 40 60 80 100 120 DUTY CYCLE (%) 32kHz ILED 20kHz 6 LEDs VI = 4V N RSET = 4Ω L = 10µH VOUT 1kHz LX VIN = 4V R1 = 4Ω L1 = 22µH FIGURE 5. DIMMNG LINEARITY (FB VOLTAGE) vs DUTY CYCLE FIGURE 6. PWM DIMMING AT 1kHz, D = 1% 4 FN6264.2 April 10, 2007 ISL97634 VOUT VOUT LX LX PWM/EN VIN = 4V ILED R1 = 4Ω L1 = 22µH PWM/EN ILED VIN = 4V R1 = 4Ω L1 = 22µH FIGURE 7. PWM DIMMING AT 1kHz, D = 1% ZOOM IN FIGURE 8. PWM DIMMING AT 1kHz, D = 99% VOUT LX PWM/EN ILED R1 = 4Ω VIN = 4V L1 = 22µH FIGURE 9. PWM DIMMING AT 20kHz, D = 50% Detailed Description The ISL97634 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 ISL97634 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 peak forward current of the LED is set using the RSET resistor. In the steady state mode, the LED peak current is given by the following equation: V FB I LED = -------------R SET (EQ. 1) pulse width modulated the output current. It is well understood that the LED brightness is a linear function of the LED current. In addition, the average LED current corresponds to the duty cycle “D” of the PWM signal as: V FB I LED – AVG = -------------- ⋅ D R SET (EQ. 2) As a result, PWM signal provides a means to dim the LED brightness. PWM dimming offers the best LEDs matching over DC dimming. It is because the LED peak current operating point is far away from the knee of the diode I-V curve where part to part variations are high. The PWM dimming test results are shown in Figure 6 with two PWM frequencies, 1kHz and 20kHz. The vertical scale parameter FB is proportional to the current and therefore the brightness. For the ISL97634, PWM dimming provides linear dimming adjustment with low frequency signal, such as 1kHz and below. The applied PWM dimming signal can be up to 32kHz PWM Dimming The ISL97634’s PWM/EN pin can be tied permanently to high for a fixed current operation. On the other hand, the ISL97634 can be applied with an external PWM signal to 5 FN6264.2 April 10, 2007 ISL97634 ; however, the dimming linearity is compromised at low duty cycles as their durations are too short for the ISL97634’s control loop to respond properly. This non ideality behavior does not cause any functional problem. The PWM dimming linear responses in Figure 5 are expanded in Figure 10. At 1kHz PWM dimming, the duty cycl