Preliminary Datasheet LP3302S High Performance, Constant Current Switching Regulator For White LED General Description The LP3302S is a 1.1MHz PWM boost switching regulator designed for constant- current white LED driver applications. The LP3302S can drive a string of up to 8 white LEDs from a 3.3V supply or 3S9P white LEDs from a 5V supply in series, ensuring uniform brightness and eliminating several ballast resistors. The LP3302S implements a constant frequency 1.1MHz 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 250mV, which reduces the power dissipation in the current setting resistor. Highly integration and internal compensation network minimizes as 5 external component counts. Optimized operation frequency can meet the requirement of small LC filters value and low operation current with high efficiency. Features High Efficiency: 88% 1.1MHz Fixed-Frequency PWM Operation Maximum Output Voltage up to 27.5V Operating Range : 2.7V to 6V Shutdown Supply Current:<1uA Available in T/SOT23-6 Package Built-in Over Voltage Protection Minimize the External Component RoHS Compliant and 100% Lead Pb-Free Applications WLED Backlight driver OLED Backlight driver PDA DSC Camera Flash WLED driver Typical Application Circuit Ordering Information Vin LP3302S 4.7uH 1uF + 6 B6: SOT23-6 4 Vin EN OUT GND F:Pb-free J6:TSOT23-6 LX 1 + 1uF FB 5 3 2 LP3302S Pin Configurations Marking information Please view website. SOT23-6/TSOT23-6 LP3302S –02 Version 1.2 Datasheet Feb.-2012 www.lowpowersemi.com Page 1 of 11 Preliminary Datasheet LP3302S Application Circuit Vin Vin Panel Panel 4.7uH 4.7uH + + + 1 2.2uF GND 4 EN 5 OUT Vin 4 3 FB LX 6 5 OUT Vin 2.2uF GND 6 2.2uF LX 2.2uF 1 + EN 3 FB LP3302S 2 2 LP3302S Rset 5.1 Rset 12 LP3302 for 6pcs Application Circuit Vin LP3302 for 2X6pcs Application Circuit Panel Vin Panel 4.7uH 4.7uH EN FB 5 6 3 4 Vin EN 2.2uF LX OUT + 2.2uF OUT GND 4 Vin LX 6 2.2uF GND 2.2uF + 1 + 1 + 3 2 LP3302S 2 LP3302S FB 5 Rset 12 LP3302 for 7pcs Application Circuit Rset 5.1 LP3302 for 2X7pcs Application Circuit Vin 4.7uH Panel + 1 + 4 Vin EN 2.2uF LX 6 OUT GND 2.2uF FB 5 3 2 LP3302S LP3302 for 21pcs Application Circuit LP3302S –02 Version 1.2 Datasheet Feb.-2012 Rset 2 www.lowpowersemi.com Page 2 of 11 Preliminary Datasheet LP3302S Functional pin description SOT-23-6 TSOT23-6 Pin Name Pin Function 1 LX Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track area to reduce EMI. 2 GND Ground Pin 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. 3 Chip Enable (Active High). Voltage sensing input to trigger the function of over voltage protection. Note that this pin is high impedance. There should be a pull low 100kΩ resistor connected to GND when the control signal is floating. 4 EN 5 OUT OVP Pin. Overvoltage Sense. When VOUT is greater than 27.5V, the internal N-channel MOSFET turns off until VOUT drops below 27V, then the IC reenters start. Connect a 1uF capacitor from OUT to GND. 6 VIN Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input noise. Function Block Diagram LP3302S –02 Version 1.2 Datasheet Feb.-2012 www.lowpowersemi.com Page 3 of 11 Preliminary Datasheet LP3302S Absolute Maximum Ratings Supply Input Voltage---------------------------------------------------------------------------------------------------−0.3V to 6.5V LX Input Voltage --------------------------------------------------------------------------------------------------------−0.3V to 36V OVP Voltage--------------------------------------------------------------------------------------------------------------−0.3V to 28V The Other Pins ----------------------------------------------------------------------------------------------------------−0.3V to 5.5V Power Dissipation, PD @ TA = 25°C SOT-23-6 -------------------------------------------------------------------------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 Electrical Characteristics Parameter Symbol Test Condition Min Typ. Max Units 6 V System Supply Input Operation voltage Range VDD 2.7 Under Voltage Lock Out VDD Supply Current IDD FB=0V, Switching 0.8 1.3 mA Shut Down Current IDD VEN < 0.4V 0.1 1 uA 2.4 Line Regulation VIN : 3.0~4.3V V 3 % 1.1 MHz Oscillator Operation Frequency 0.8 FOSC Maximum Duty Cycle 89 Dimming Frequency 100 Feedback Voltage LP3302S 235 92 250 96 % 100k Hz 270 mV MOSFET On Resistance of MOSFET RDS(ON) 0.8 Ω Protection OVP Threshold 27.5 VOVP OVP Sink Current OCP Shut Down Voltage VEN Enable Voltage VEN LP3302S –02 Version 1.2 Datasheet 29 V 5 μA 850 mA 0.4 1.5 Feb.-2012 www.lowpowersemi.com V V Page 4 of 11 Preliminary Datasheet LP3302S Typical Operating Characteristics LP3302S –02 Version 1.2 Datasheet Feb.-2012 www.lowpowersemi.com Page 5 of 11 LP3302S –02 Version 1.2 Datasheet Feb.-2012 Preliminary Datasheet LP3302S www.lowpowersemi.com Page 6 of 11 LP3302S –02 Version 1.2 Datasheet Feb.-2012 Preliminary Datasheet LP3302S www.lowpowersemi.com Page 7 of 11 LP3302S –02 Version 1.2 Datasheet Feb.-2012 Preliminary Datasheet LP3302S www.lowpowersemi.com Page 8 of 11 Preliminary Datasheet LP3302S Applications Information LED Current Control The LP3302S 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. 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 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. Inductor Selection The recommended value of inductor for 2 to 6 WLEDs applications are 2.2 to 22µH. Small size and better efficiency are the major concerns for portable device, such as LP3302S 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 LP3302S 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. LP3302S –02 Version 1.2 Datasheet Feb.-2012 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%. www.lowpowersemi.com Page 9 of 11 Preliminary Datasheet LP3302S www.lowpowersemi.com Page 10 of 11 Packing information LP3302S –02 Version 1.2 Datasheet Feb.-2012 LP3302S –02 Version 1.2 Datasheet Feb.-2012 Preliminary Datasheet LP3302S www.lowpowersemi.com Page 11 of 11