Preliminary Datasheet LP3303 No Schttoy, High Performance, Constant Current Switching Regulator For 9PCS White LED General Description Features The LP3303 is a 1.0MHz PWM boost switching regulator designed for constant- current white LED driver applications. The LP3303 can drive a string of up to 8 white LEDs from a 3.6V in series, ensuring uniform brightness and eliminating several ballast resistors. The LP3303 implements a constant frequency 1.0MHz PWM control scheme. The high frequency PWM operation also saves board space by reducing external component sizes. To improve efficiency, the feedback voltage is set to 200mV, which reduces the power dissipation in the current setting resistor. Highly integration and internal compensation network minimizes as 3 external component counts. Optimized operation frequency can meet the requirement of small LC filters value and low operation current with high efficiency. Ordering Information High Efficiency: 86% 1.2MHzFixed-Frequency PWM Operation Maximum Output Voltage up to 28V Operating Range : 2.7V to 16V Shutdown Supply Current:<1uA Available in SOT23-6 Package Built-in Over Voltage Protection Minimize the External Component RoHS Compliant and 100% Lead (Pb)-Free Applications WLED Blacklight driver OLED Blacklight driver PDA DSC Camera Flash WLED driver Typical Application Circuit VIN 22uH Pb-Free B6:SOT23-6 OUT 5 LP3303 4 CTRL FB 3 2 Pin Configurations VIN SW 6 F: 1uF 1 1uF GND LP3303 Rset 10R Marking information Please view website. LP3303 –03 Ver. 1.3 Datasheet Feb.-2009 Page 1 of 7 Preliminary Datasheet Functional pin description LP3303 Pin Name Pin Function 1 SW Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track area to reduce EMI. 2 GND Ground Pin 3 FB Feedback Reference Voltage Pin. Series connect a resistor between WLED and ground as a current sense. Sense the current feedback voltage to set the current rating. 4 CTRL 5 OUT Output Pin.Connect to output capacitor and LEDs.Minimize trace between this pin and output capacitor to reduce EMI. 6 VIN Supply Input Voltage Pin. Bypass 1uF X5R or X7R capacitor to GND to reduce the input noise. SOT-23-6 Chip Enable (Active High) and dimming Control pin. Function Block Diagram Absolute Maximum Ratings Supply Input Voltage(VIN)-------------------------------------------------------------------------------------------−0.3V to 16V LX Input Voltage --------------------------------------------------------------------------------------------------------−0.3V to 36V OUT Pin Voltage---------------------------------------------------------------------------------------------------------−0.3V to 29V CTRL Pin Voltage-------------------------------------------------------------------------------------------------------−0.3V to 10V FB Pins -------------------------------------------------------------------------------------------------------------------−0.3V to 2.0V Power Dissipation, PD @ TA = 25°C SOT-23-5 ------------------------------------------------------------------------0.455W Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------------ 260°C Operation Temperature Range ---------------------------------------------------------------------------------−40°C to 80°C Storage Temperature Range ----------------------------------------------------------------------------------------−65°C to 150°C LP3303 –03 Ver. 1.3 Datasheet Feb.-2009 Page 2 of 7 Preliminary Datasheet LP3303 Electrical Characteristics Parameter Symbol Test Condition Min Typ Max Units 16 V System Supply Input Operation voltage Range VDD Under Voltage Lock Out VDD Supply Current IDD FB=0V, Switch Shut Down Current IDD VEN < 0.4V Line Regulation 2.7 2.5 VIN : 3.0~4.3V V 1 2.5 mA 0.1 1 uA 3 % Oscillator Operation Frequency FOSC 0.9 Maximum Duty Cycle 90 Dimming Frequency 100 Feedback Voltage LP3303 191 1.0 1.2 MHz % 200 10k Hz 210 mV MOSFET On Resistance of MOSFET RDS(ON) 0.5 Ω VOVP 29 V 5 μA 750 mA Protection OVP Threshold OVP Sink Current OCP Shut Down Voltage VEN Enable Voltage VEN LP3303 –03 Ver. 1.3 Datasheet Feb.-2009 0.4 1.5 V V Page 3 of 7 Preliminary Datasheet Typical Operating Characteristics LP3303 –03 Ver. 1.3 Datasheet Feb.-2009 LP3303 Page 4 of 7 Preliminary Datasheet LP3303 –03 Ver. 1.3 Datasheet Feb.-2009 LP3303 Page 5 of 7 Preliminary Datasheet LP3303 Applications Information LED Current Control The LP3303 regulates the LED current by setting the current sense resistor (Rset) connecting to feedback and ground. The internal feedback reference voltage is 200mV. The LED current can be set from following equation easily. ILED(mA)=200mV/Rset In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for Rset selection is shown below. Rset Resistor Value selection ILED(mA) RSET(Ω) 20 10 15 13.3 12 16.6 10 20 5 40 Inductor Selection b. Using a DC Voltage 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 RSET 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. VIN 22uH 1uF 6 VIN SW 1 1uF OUT 5 ON 4 CTRL FB 3 R1 5K 2 OFF GND LP3303 Dimming control a. Using a PWM Signal to CTRL Pin For controlling the LED brightness, the LP3303 can perform the dimming control by applying a PWM signal to CTRL pin. The internal soft-start and wide range dimming frequency from 100Hz to 50KHz 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 CTRL pin, in order to let the dimming control perform correctly. R2 90K 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%. VIN 22uH VIN 1 5 ON 4 OFF FB CTRL FB 3 R1 5K 3 2 GND 5 R2 90K 2 CTRL OUT LP3303 OUT LP3303 4 VIN GND PWM VIN SW 6 6 1uF 1uF 1 1uF 22uH 1uF Rset 10R VDC (0-2.8V) SW The recommended value of inductor for 2 to 8 WLEDs applications are 4.7 to 22µH. Small size and better efficiency are the major concerns for portable device, such as LP3303 used for mobile phone. The inductor should have low core loss at 1.4MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Rset 10R LP3303 –03 Ver. 1.3 Datasheet Feb.-2009 PWM (0-100KHz) R3 100K Rset 10R C1 0.1uF Page 6 of 7 Preliminary Datasheet LP3303 Packing information LP3303 –03 Ver. 1.3 Datasheet Feb.-2009 Page 7 of 7