EUP2571 White LED Step-Up Converter In Tiny SOT-23 Package DESCRIPTION FEATURES The EUP2571 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 EUP2571 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 0.25V feedback voltage minimizes power loss in the current setting resistor for better efficiency. The EUP2571 is available in low profile SOT23-5, SOT23-6 package. z z z z z z z z z 2.6V to 5.5V Input Range 26V Output with Over Voltage Protection High Efficiency :85 % Typical PWM Dimming Control Internal High Power 30V MOSFET Switch Fast 1.1MHz Switching Frequency Small, Low-Profile Inductors and Capacitors SOT23-5,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 DS2571 Ver1.1 May. 2007 1 EUP2571 Typical Application Circuit (continued) Figure 2. 5V to 9V/300mA Step-Up Application Pin Configurations Package Type Pin Configurations Package Type SOT23-5 Pin Configurations SOT23-6 Pin Description PIN SOT23-5 SOT23-6 LX 1 1 GND 2 2 FB 3 3 EN 4 4 IN 5 6 OUT - 5 DS2571 Ver1.1 May. 2007 DESCRIPTION Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. Common Ground Feedback Pin. Reference voltage is 0.25V. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB=0.25/ILED Chip Enable Pin. Connect to 1.4V or higher to enable device, 0.4V or less to disable device. Input Supply Voltage 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. 2 EUP2571 Ordering Information Order Number Package Type Marking Operating Temperature range EUP2571VBIR1 SOT23-5 V0 □ □ □ -40 °C to 125°C EUP2571VCIR1 SOT23-6 V0 □ □ □ -40 °C to 125°C EUP2571 □□ □ □ □ Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type V: SOT23 VB: SOT23-5 VC: SOT23-6 Block Diagram Figure 3. DS2571 Ver1.1 May. 2007 3 EUP2571 Absolute Maximum Ratings Supply Voltage ,VIN ----------------------------------------------------------------- -0.3V to 6V LX,OUT ----------------------------------------------------------------------------- -0.3V to 30V The Other Pins ---------------------------------------------------------------------- -0.3V to 6V Power dissipation, PD@ TA=25°C SOT23-6 ------------------------------------------------------------------------------- 0.4W Package Thermal Resistance SOT23-6,θJA ------------------------------------------------------------------------- 250°C/W Maximum Junction Temperature --------------------------------------------------- 125°C Lead Temperature (Soldering, 10sec.) --------------------------------------------- 260°C Storage Temperature Range ------------------------------------------------------- -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=12V, COUT=1µF, CIN=1µF, RSENSE=12Ω, TA=-40°C to 85°C. Unless otherwise noted. Typical values are at TA= 25°C) Symbol UVLO ICC1 ICC2 ICC3 Parameter Supply Voltage Under voltage Lock Out Maximum Output Voltage Supply Current Quiescent Current Shut Down current Conditions VIN rising or falling VCC=6V, Continuous Switching VCC=6V, FB=1.3V, No Switching VCC=6V, VEN<0.4V EUP2571 Min Typ Max. Unit -2.2 ----- -2.4 -0.8 115 0.1 6 2.6 26 1.5 250 1 V V V mA µA µA Oscillator Fosc Operation Frequency 0.8 1.1 1.3 MHz Dmax Maximum Duty Cycle 89 92 96 % TA=25℃ 237 250 263 TA=-40°C to 85°C 230 250 270 -- 1.05 1.5 Ω 0.4 0.75 1.2 A 0.4 0.7 -- V Enable Voltage -- 0.7 1.2 V EN Pin Pull Low Current -- -- 0.1 µA Falling 24.5 25.7 26.5 Rising 26.1 27.3 28.1 Reference Voltage VFB Feedback Voltage MOSFET Rds (on) On resistance of MOSFET ILX Current Limit Control and Protection VEN1 Shut Down Voltage VEN2 IEN OVP OVP Threshold DS2571 Ver1.1 May. 2007 4 mV V EUP2571 Typical Operating Characteristics Efficiency vs. Vin (Driving 1WLED) Efficiency vs. Vin (Driving 2WLEDs) Efficiency vs. Vin (Driving 3WLEDs) Efficiency vs. Vin (Driving 5WLEDs) Efficiency vs. Vin (Driving 7WLEDs) DS2571 Ver1.1 May. 2007 5 EUP2571 DS2571 Ver1.1 May. 2007 6 EUP2571 DS2571 Ver1.1 May. 2007 7 EUP2571 DS2571 Ver1.1 May. 2007 8 EUP2571 DS2571 Ver1.1 May. 2007 9 EUP2571 Application Information LED Current Control The EUP2571 regulates the LED current by setting the current sense resistor (R2) connecting to feedback and ground. The internal feedback reference voltage is 0.25V. The LED current can be set from following equation easily. R2 = 0.25V 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. b. Using a DC Voltage R2 Resistor Value selection ILED (mA) R2 (Ω) 5 49.9 10 24.9 12 21 15 16.5 20 12.4 Figure 4. PWM Dimming Control Using the EN Pin 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 5. 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 5 sets dimming control of LED current from 20mA to 0mA. 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 EUP2571 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 EUP2571 can perform the dimming control by applying a PWM signal to EN pin. 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. Figure 5. Dimming Control Using a DC Voltage Figure 6. Recommended Soft-Start Circuit DS2571 Ver1.1 May. 2007 10 EUP2571 Constant Output Voltage for Backlight of Main Panel and Flashlight 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 7. 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 7, output current is from 20.5mA to 5.5mA by adjusting the PWM duty cycle from 10% to 90%. Figure 8 is an application of EUP2571 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. R3 = VOUT − 3VFb − VDS --------------------------(2) Ib R4 = VOUT − 3VFf − VDS --------------------------(3) If VDS = Ib × R DS(ON ) ---------------------------------(4) Figure 7. Filtered PWM Signal for LED Dimming Control Figure 8. Constant Output Voltage for Backlight and Flashlight DS2571 Ver1.1 May. 2007 11 EUP2571 Constant Output Voltage for Backlight of Main Panel and Keypad Figure 9 is another application of EUP2571 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 5. The following formula (5)(6) can determine the resistors of Figure 9. R3 = VOUT − 3VFb − VDS ----------------------------(5) Ib R4 = R5 = R6 = VOUT − 3VFk ----------------------(6) Ik VDS = Ib × R DS(ON) ----------------------------------(7) Figure 9. Constant Output Voltage for Backlight and Keypad DS2571 Ver1.1 May. 2007 12 EUP2571 Packaging Information SOT23-5 SYMBOLS MILLIMETERS INCHES MIN. MAX. MIN. MAX. A - 1.30 - 0.052 A1 0.00 0.15 0.000 0.006 D 2.90 0.114 E1 1.60 0.063 E 2.60 3.00 0.102 0.118 L 0.30 0.60 0.012 0.024 b 0.30 0.50 0.012 0.020 e DS2571 Ver1.1 May. 2007 0.95 0.037 13 EUP2571 Packaging Information SOT23-6 SYMBOLS A A1 b D E1 e E L DS2571 Ver1.1 May. 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 14 INCHES MIN. 0.000 0.012 MAX. 0.057 0.006 0.020 0.114 0.063 0.037 0.102 0.012 0.118 0.024