EUP2584A White LED Step-Up Converter In Tiny SOT-23 Package DESCRIPTION FEATURES The EUP2584A is a constant current step-up converter specifically designed to drive white LEDs. The Step-up converter topology allows series connection of the white LEDs so the LED currents are identical for uniform brightness. The EUP2584A switches at 1.1MHz, allowing the use of tiny external components. The input and output capacitor can be as small as 1µF, saving space and cost versus alternative solutions. A low 0.3V feedback voltage minimizes power loss in the current setting resistor for better efficiency. EUP2584A is enhanced with Soft-Start function and that could significantly reduce noise induced by capacitor. The EUP2584A is available in low profile SOT23-6 package. z z z z z z z z z z 2.6V to 5.5V Input Range 27V Output with Over Voltage Protection High Efficiency :85 % Typical Internal Soft-Start PWM Dimming Control Internal High Power 30V MOSFET Switch Fast 1.1MHz Switching Frequency Small, Low-Profile Inductors and Capacitors SOT23-6 Package RoHS Compliant and 100% Lead (Pb)-Free APPLICATIONS z z z z z Mobile Phone Digital Still Camera PDAs, Handheld Computers MP3 Players GPS Receivers Typical Application Circuit Figure 1. White LED Application DS2584A Ver1.0 Nov. 2007 1 EUP2584A Pin Configurations Package Type Pin Configurations SOT23-6 Pin Description PIN SOT23-6 EN 1 OUT 2 IN 3 DESCRIPTION Chip Enable Pin. Connect to 1.4V or higher to enable device, 0.3V or less to disable device. Overvoltage Sense. When VOUT is greater than 27V, the internal N-channel MOSFET turns off until VOUT drops below 25V, then the IC reenters start. Connect a 1uF capacitor from OUT to GND. Input Supply Voltage LX 4 Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. GND 5 FB 6 Common Ground Feedback Pin. Reference voltage is 0.3V. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB=0.3/ILED DS2584A Ver1.0 Nov. 2007 2 EUP2584A Ordering Information Order Number Package Type Marking Operating Temperature range EUP2584AVIR1 SOT23-6 f0 □ □ □ □ -40 °C to 125°C EUP2584A □ □ □ □ Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type V: SOT23 Block Diagram Figure 2. DS2584A Ver1.0 Nov. 2007 3 EUP2584A Absolute Maximum Ratings Supply Voltage ,VIN ----------------------------------------------------------------LX,OUT ----------------------------------------------------------------------------The Other Pins ---------------------------------------------------------------------Power dissipation, PD@ TA=25°C SOT23-6 ------------------------------------------------------------------------------Package Thermal Resistance SOT23-6,θJA ------------------------------------------------------------------------Maximum Junction Temperature --------------------------------------------------Lead Temperature (Soldering, 10sec.) --------------------------------------------Storage Temperature Range --------------------------------------------------------- -0.3V to 6V -0.3V to 30V -0.3V to 6V 0.4W 250°C/W 125°C 260°C -65°C to 150°C Operating Conditions Junction Temperature Range ------------------------------------------------------- -40°C to 125°C Supply Voltage , VIN----------------------------------------------------------------- 2.6V to 5.5V Electrical Characteristics (VIN =3.6V, VOUT=18V, COUT=1µF, CIN=1µF, RSENSE=15Ω, TA=-40°C to 85°C. Unless otherwise noted. Typical values are at TA= 25°C) Symbol Parameter Conditions Supply Voltage UVLO ICC1 ICC2 ICC3 Under Voltage Lock Out Maximum Output Voltage Supply Current Quiescent Current Shutdown current VIN Rising VIN Falling No Switching VCC=6V, Continuous Switching VCC=6V, FB=1.3V, No Switching VCC=6V, VEN<0.3V EUP2584A Min Typ Max. Unit -2.2 1.95 ----- -2.4 2.15 -0.8 115 0.1 6 2.6 2.35 30 1.3 150 1 V V mA µA µA V Oscillator Fosc Operation Frequency 0.8 1.1 1.3 MHz Dmax Maximum Duty Cycle 89 92 96 % 285 300 315 mV -- 1 1.5 Ω 0.4 0.8 1.2 A Reference Voltage VFB Feedback Voltage MOSFET Rds (on) On resistance of MOSFET ILX Current Limit Control and Protection VEN1 Shutdown Voltage 0.3 0.7 -- V VEN2 Enable Voltage -- 0.7 1.4 V EN Pin Pull Low Current -- -- 0.1 µA Falling 24.5 25.7 26.5 Rising 26.1 27.3 28.1 IEN OVP OVP Threshold DS2584A Ver1.0 Nov. 2007 4 V EUP2584A Typical Operating Characteristics Efficiency vs. VIN (Driving 3WLEDs) Efficiency vs. Vin (Driving 1WLED) 85% 90% IO=15mA IO=20mA IO=15mA 83% 82% 84% 82% 80% 80% 2.5 Vin (V) 3 2 3.5 84% 3 4 5 Vin (V) VIN=2.6V Driving 2LEDs Stability Efficiency vs. VIN (Driving 6WLEDs) IO=20mA IO=15mA 82% Efficiency (%) 86% 81% 2 IO=20mA 88% Efficiency (%) Efficiency (%) 84% 80% 78% 76% 74% 2 3 4 5 6 Vin (V) VIN=5V Driving 2LEDs Stability VIN=3.6V Driving 2LEDs Stability DS2584A Ver1.0 Nov. 2007 5 6 EUP2584A VIN=2.6V Driving 4LEDs Stability VIN=3.6V Driving 4LEDs Stability VIN=5V Driving 4LEDs Stability VIN=2.6V Driving 6LEDs Stability VIN=3.6V Driving 6LEDs Stability VIN=5V Driving 6LEDs Stability DS2584A Ver1.0 Nov. 2007 6 EUP2584A VIN=3.6V Driving 2LEDs Inrush Current VIN=3.6V Driving 4LEDs Inrush Current VIN=3.6V Driving 6LEDs Inrush Current VIN=3.6V Driving 6LEDs 100Hz PWM Dimming VIN=3.6V Driving 6LEDs 1KHz PWM Dimming VIN=3.6V Driving 6LEDs 10KHz PWM Dimming DS2584A Ver1.0 Nov. 2007 7 EUP2584A VIN=3.6V Driving 6LEDs 100KHz PWM Dimming DS2584A Ver1.0 Nov. 2007 8 EUP2584A Application Information b. Using a DC Voltage LED Current Control The EUP2584A regulates the LED current by setting the current sense resistor (R2) connecting to feedback and ground. The internal feedback reference voltage is 0.3V. The LED current can be set from following equation easily. Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming control using a DC voltage circuit is shown in Figure 4. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to VFB increases and the voltage drop on R2 decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V, the selection of resistors in Figure 4 sets dimming control of LED current from 20mA to 0mA. R2 = 0.3V I LED --------------------------------------(1) In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for R2 selection is shown below. R2 Resistor Value selection ILED (mA) R2 (Ω) 5 60 10 30 12 25 15 20 20 15 Inductor Selection The recommended value of inductor for 2 to 6 WLEDs applications are 4.7 to 22µH. Small size and better efficiency are the major concerns for portable device, such as EUP2584A used for mobile phone. The inductor should have low core loss at 1.1MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Dimming Control a. Using a PWM Signal to EN Pin For controlling the LED brightness, the EUP2584A can perform the dimming control by applying a PWM signal to EN pin. The internal soft-start and wide range dimming frequency from 100Hz to 100KHz can insignificantly reduce audio noise when dimming. The average LED current is proportional to the PWM signal duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of EN pin, in order to let the dimming control perform correctly. Nov. 2007 c. Using a Filtered PWM signal Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. A filtered PWM signal acts as the DC voltage to regulate the output current. The recommended application circuit is shown in the Figure 6. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2.8V PWM signal should be above 2kHz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get different output current. According to the application circuit of Figure 5, output current is from 20.5mA to 5.5mA by adjusting the PWM duty cycle from 10% to 90%. Figure 5. Filtered PWM Signal for LED Dimming Control Figure 3. PWM Dimming Control Using the EN Pin DS2584A Ver1.0 Figure 4. Dimming Control Using a DC Voltage 9 EUP2584A Constant Output Voltage for Backlight of Main Panel and Flashlight Constant Output Voltage for Backlight of Main Panel and Keypad Figure 6 is an application of EUP2584A for backlight of main panel and flashlight. Setting the divider-resistors (R1 & R2) is to get a constant output voltage that depends on the forward voltage and the numbers of series-LEDs. There are three kinds of mode controlled by the switches - backlight mode /flashlight mode /backlight + flashlight mode. It can turn on backlight or flashlight at one time or both at the same time. Applying different duty cycle of PWM signal above 22kHz to backlight's switch can also control the brightness. The following formula (2)(3) can determine R3 and R4. Figure 7 is another application of EUP2584A for backlight and keypad. Setting the divider-resistors (R1 & R2) is to get a constant output voltage that depends on the forward voltage and the numbers of series-LEDs. It can turn on backlight of main panel and keypad at the same time. Applying different duty cycle of PWM signal above 22kHz to the backlight's switch can also control the brightness of main panel's backlight. The keypad's backlight will keep the same brightness during the dimming control of main panel. Otherwise the brightness of keypad's s backlight can also change during the dimming control of main panel by using the application circuit as figure 4. The following formula (5)(6) can determine the resistors of Figure 8. R3 = VOUT − 3VFb − VDS --------------------------(2) Ib R4 = VOUT − 3VFf − VDS --------------------------(3) If R3 = VDS = Ib × R DS(ON) ---------------------------------(4) VOUT − 3VFb − VDS ----------------------------(5) Ib R4 = R5 = R6 = VOUT − 3VFk ----------------------(6) Ik VDS = Ib × R DS(ON) ----------------------------------(7) Figure 6. Constant Output Voltage for Backlight and Flashlight Figure 7. Constant Output Voltage for Backlight and Keypad DS2584A Ver1.0 Nov. 2007 10 EUP2584A Packaging Information SOT23-6 SYMBOLS A A1 b D E1 e E L DS2584A Ver1.0 Nov. 2007 MILLIMETERS MIN. MAX. 1.45 0.00 0.15 0.30 0.50 2.90 1.60 0.95 2.60 3.00 0.3 0.60 11 INCHES MIN. MAX. 0.057 0.000 0.006 0.012 0.020 0.114 0.063 0.037 0.102 0.118 0.012 0.024