EUP2518 White LED Step-Up Converter In TSOT-23 Package DESCRIPTION FEATURES The EUP2518 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 EUP2518 switches at 1.1MHz, allowing the use of tiny external components. The output capacitor can be as small as 0.22uF, saving space and cost versus alternative solutions. A low 104mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. EUP2518 is enhanced with Soft-Start function and that could significantly reduce noise induced by capacitor. The EUP2518 is available in low profile TSOT23-6 package. 2.6V to 5.5V Input Range 27V Output with Over Voltage Protection High Efficiency :87 % Typical Internal Soft-Start PWM Dimming Control Internal High Power 30V MOSFET Switch Fast 1.1MHz Switching Frequency Small, Low-Profile Inductors and Capacitors TSOT23-6 Package RoHS Compliant and 100% Lead (Pb)-Free APPLICATIONS Mobile Phone Digital Still Camera PDAs, Handheld Computers MP3 Players GPS Receivers Typical Application Circuit Figure 1. White LED Application DS2518 Ver1.0 Mar. 2008 1 EUP2518 Pin Configurations Package Type Pin Configurations TSOT23-6 Pin Description PIN TSOT23-6 LX 1 Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. GND 2 FB 3 EN 4 OUT 5 IN 6 Common Ground Feedback Pin. Reference voltage is 104mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB=104/ILED 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 0.22uF capacitor from OUT to GND. Input Supply Voltage DS2518 Ver1.0 Mar. 2008 DESCRIPTION 2 EUP2518 Ordering Information Order Number Package Type Marking Operating Temperature Range EUP2518OIR1 TSOT23-6 50 □ □ □ □ -40 °C to 85°C EUP2518 □ □ □ □ Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type O: TSOT Block Diagram Figure 2. DS2518 Ver1.0 Mar. 2008 3 EUP2518 Absolute Maximum Ratings Supply Voltage ,VIN ----------------------------------------------------------------LX,OUT ----------------------------------------------------------------------------The Other Pins ---------------------------------------------------------------------Package Thermal Resistance TSOT23-6,θJA ----------------------------------------------------------------------Maximum Junction Temperature --------------------------------------------------Lead Temperature (Soldering, 10sec.) --------------------------------------------Storage Temperature Range --------------------------------------------------------- -0.3V to 6V -0.3V to 30V -0.3V to 6V 220°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=0.22µF, CIN=1µF, RFB=5.1Ω, 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 Min EUP2518 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 % Feedback Voltage 94 104 114 mV On resistance of MOSFET -- 1 1.5 Ω Current Limit 0.4 0.8 1.2 A Reference Voltage VFB MOSFET RDS(ON) ILX 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 DS2518 Ver1.0 Mar. 2008 4 V EUP2518 Typical Operating Characteristics Efficiency vs LED Current Startup Waveforms into an Open Load 91 VEN EFFICENCY (%) 87 VOUT 83 79 VSW 6 LED 3 LED 4 LED 75 5 10 15 20 LED CURRENT (mA) Startup Waveforms Steady State Operation(VIN=3.6V, 3 LEDs, 20mA) VEN VSW VOUT VOUT IL IIN 10KHz 50% Duty Cycle PWM Dimming 1KHz 50% Duty Cycle PWM Dimming VEN VEN VOUT VOUT IIN IIN DS2518 Ver1.0 Mar. 2008 5 EUP2518 Application Information b. Using a DC Voltage LED Current Control The EUP2518 regulates the LED current by setting the current sense resistor (RFB) connecting to feedback and ground. The internal feedback reference voltage is 104mV. The LED current can be set from following equation easily. R FB = 104mV I LED -------------------------------------(1) In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for RFB selection is shown below. RFB Resistor Value selection RFB (Ω) ILED (mA) 5 21 10 10.4 15 6.93 20 5.2 CAP and Inductor Selection The recommended value of inductor for 2 to 6 WLEDs applications are 10µH to 47µH. Small size and better efficiency are the major concerns for portable device. A 22µH inductor with low DCR (Inductor resistance) is recommended to improve efficiency. To avoid inductor saturation current rating should be considered. A 1µF ceramic capacitor is recommended for the input capacitance in the real system, and a larger capacitor will get smaller input voltage ripple. A 0.22uF output ceramic capacitor is sufficient for most applications. Dimming Control a. Using a PWM Signal to EN Pin For controlling the LED brightness, the EUP2518 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. 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 RFB decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2V, the selection of resistors in Figure 4 sets dimming control of LED current from 20mA to 0mA. Figure 4. Dimming Control Using a DC Voltage 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. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2V 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 DS2518 Ver1.0 Mar. 2008 6 EUP2518 Layout Considerations The input bypass capacitor C2, as shown in Figure 1, must be placed close to the IC. This will reduce copper trace resistance which effects input voltage ripple of the IC. The output capacitor, C1, should also be placed close to the IC. Any copper trace connections for the C1 capacitor can increase the series resistance, which directly effects output voltage ripple. The feedback resistors RFB should be kept close to the FB pin to minimize copper trace connections that can inject noise into the system. The ground connection for the feedback resistor network should connect directly to GND pin. Trace connections made to the inductor and schottky diode should be minimized to reduce EMI and increase overall efficiency. DS2518 Ver1.0 Mar. 2008 7 EUP2518 Packaging Information TSOT23-6 SYMBOLS A A1 b D E1 e E L DS2518 Ver1.0 Mar. 2008 MILLIMETERS MIN. MAX. 1.00 0.00 0.15 0.30 0.50 2.90 1.60 0.95 2.60 3.00 0.3 0.60 8 INCHES MIN. 0.000 0.012 MAX. 0.039 0.006 0.020 0.114 0.063 0.037 0.102 0.012 0.118 0.024