LP3300 Preliminary Datasheet High Performance, Constant Current Switching Regulator for White LED General Description The LP3300 is a 1.2MHz PWM boost switching regulator designed for constantcurrent white LED driver applications. The LP3300 can drive a string of up to 4 white LEDs from a 3.2V supply or 6 white LEDs from a 5V supply in series, ensuring uniform brightness and eliminating several ballast resistors. The LP3300 implements a constant frequency 1.2MHz 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 95 mV, 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% 1.2MHz Fixed-Frequency PWM Operation Maximum Output Voltage up to 29V VIN Operating Range : 2.7V to 15V Shutdown Supply Current:<1uA Available in SOT23-5 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 Ordering Information LP3300 □ □ L1 22uH LP3300 □ 5 + Cin 1uF EN F:Pb-Free Package Type B5: SOT-23-5 D SS0520 Vin SW SHDN 0.22uF ON 2 GND FB 3 VFB=0.095 OFF R1 6.34 Marking information Please view website. Dec.-2005 + Cout 4 Pin Configurations LP3300-datasheet 1 1 -1 Preliminary Datasheet LP3300 Functional Pin Description SOT-23-5 Pin Name Pin Function Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track 1 LX 2 GND area to reduce EMI. Ground Pin Feedback Reference Voltage Pin. Series connect a resistor between WLED 3 FB and ground as a current sense. Sense the current feedback voltage to set the current rating. Chip Enable (Active High). Voltage sensing input to trigger the function of 4 SHDN 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. 5 VIN Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input noise. Function Block Diagram LP3300-datasheet Dec.-2005 2 -2 LP3300 Preliminary Datasheet Absolute Maximum Ratings Supply Input Voltage--------------------------------------------------------------------------------------------------−0.3V to 15V LX Input Voltage -------------------------------------------------------------------------------------------------------−0.3V to 36V OVP Voltage------------------------------------------------------------------------------------------------------------−0.3V to 29V The Other Pins ---------------------------------------------------------------------------------------------------------−0.3V to 10V 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 Junction Temperature Range ----------------------------------------------------------------------------------------0°C to 125°C Storage Temperature Range ----------------------------------------------------------------------------------------−65°C to 150°C Operation Junction Temperature Range --------------------------------------------------------------------------0°C to 125°C Electrical Characteristics Parameter Symbol Test Condition Min Typ Max Units 15 V System Supply Input Operation voltage Range VDD 2.7 Under Voltage Lock Out VDD -- Supply Current IDD Shut Down Current IDD Line Regulation FB=0V, Switch 2.2 V 2 2.5 mA VEN < 0.4V 0.1 1 uA VIN : 3.0~4.3V 3 % 1.2 MHz Oscillator Operation Frequency FOSC Maximum Duty Cycle 85 Dimming Frequency 100 % 100k Hz 104 V Reference Voltage Feedback Voltage (Note 4) LP3300 86 95 RDS(ON) -- 0.8 MOSFET On Resistance of MOSFET Ω Protection OVP Threshold VOVP OVP Sink Current OCP Shut Down Voltage VEN -- Enable Voltage VEN 1.5 LP3300-datasheet Dec.-2005 3 -3 29 V 5 μA 750 mA 0.4 V V Preliminary Datasheet Typical Operating Characteristics LP3300-datasheet Dec.-2005 4 -4 LP3300 Preliminary Datasheet LP3300-datasheet Dec.-2005 5 -5 LP3300 Preliminary Datasheet LP3300 Applications Information The LP3300 regulates the LED current by setting the current sense resistor (R1) connecting to feedback and ground. As shown in Table 1, the LP3300 Over voltage protetion is 29V and the LP3300 feedback voltage (VFB) is 95mV. The LED current (ILED) can be set by a resistor R1. In order to have an accurate LED current, a precision resistor is preferred (1% is recommended). Dimming Control a. Using a PWM Signal to EN PinFor controlling the LED brightness, the LP3300 can perform the dimming control by applying a PWM signal to EN pin. The internal soft start and the wide range dimming frequency from100 to100kHz can eliminate inrush current and 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. 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 5. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to VFB increases and the voltage drop on R2 decreases, Ie 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. LP3300-datasheet Dec.-2005 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 6 -6 Preliminary Datasheet output current as Figure 7. According to the application circuit of Figure 6, output current is from 18.7mA to 1.16mA by adjusting the PWM duty cycle from 5% to 95%. Inductor Selection The recommended value of inductor for 3 to 5 WLEDs applications is 22µH. Small size and better efficiency are the major concerns for portable device, such as LP3300 used for mobile phone. The inductor should have low core loss at 1.2MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Capacitor Selection Input and output ceramic capacitors of 1µF are recommended for LP3300 applications. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges. LP3300 Diode Selection Schottky diode is a good choice for LP3300 because of its low forward voltage drop and fast reverse recovery. Using Schottky diode can get better efficiency. The high-speed rectification is also a good characteristic of Schottky diode for high switching frequency. Current rating of the diode must meet the root mean square of the peak current and output average current multiplication as following: The diode’s reverse breakdown voltage should be larger than the output voltage. SS0520 is recommended Schottky diode for rectifier. Layout Considerations A full GND plane without gap break. VCC to GND noise bypass–Short and wide connection for the 1µF MLCC capacitor between Pin6 and Pin2. Minimized LX node copper area to reduce EMI. Minimized FB node copper area and keep far away from noise sources. LP3300-datasheet Dec.-2005 7 -7 Preliminary Datasheet Packing information LP3300-datasheet Dec.-2005 8 -8 LP3300