Preliminary Datasheet LP3311S High Performance, Constant Current Switching Regulator For 8PCS White LED In Series General Description Features The LP3311S is a 1MHz PWM boost switching regulator High Efficiency: 90% designed for constant current white LED driver applications. 1MHz Fixed-Frequency PWM Operation The LP3311S can drive a string of up to 8 white LED in Maximum Output Voltage up to 29V series, ensuring uniform brightness and eliminating several Operating Range : 2.7V to 5.5V ballast resistors. The LP3311S implements a constant Shutdown Supply Current:<1uA frequency 1MHz PWM control scheme. The high frequency Available in SOT23-6 Package PWM operation also saves board space by reducing Built-in 29V Over Voltage Protection external component size. To improve efficiency, the Minimize the External Component feedback voltage is set to 200 mV, which reduces the RoHS Compliant and 100% Lead (Pb)-Free 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. Ordering Information Applications WLED Backlight driver OLED Backlight driver PDA MID/PTV LP3311S F: Pb-Free Typical Application Circuit Vin Package: 4.7uH 10uF 1uF B6: SOT23-6 Vin SW EN OVP Pin Configurations IN OVP EN 6 5 4 GND FB LP3311S R1 1 SW 2 3 GND FB SOT-23-6 LP3311s – 02 Version 2.0 Datasheet May.-2013 www.lowpowersemi.com Page 1 of 7 Preliminary Datasheet LP3311S Functional pin description SOT-23-6 Pin Name Pin Function Switch Pin. Connect this Pin to inductor and catch diode. Minimize the 1 SW 2 GND track area to reduce EMI. Ground Pin Feedback Reference Voltage Pin. Series connect a resistor between 3 FB WLED 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 over voltage protection. Note that this pin is high impedance. There EN should be a pull low 100kΩ resistor connected to GND when the control signal is floating. 5 OVP 6 Vin Over voltage pin. Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input noise. Function Block Diagram IN OUT Soft start 200 mV FB ∑ EN Q R PWM S A1 PWM_COMP. Driver Over voltage OTA 4mS DELAY SW RS SLOPE ENABLE 1MHz OBCILLATOR GND LP3311s – 02 Version 2.0 Datasheet May.-2013 www.lowpowersemi.com Page 2 of 7 Preliminary Datasheet LP3311S Absolute Maximum Ratings Supply Input Voltage---------------------------------------------------------------------------------------------------−0.3V to 6.0V SW Input Voltage --------------------------------------------------------------------------------------------------------−0.3V to 43V The Other Pins ----------------------------------------------------------------------------------------------------------−0.3V to 5.5V Power Dissipation, PD @ TA = 25°C TSOT-23-5/6-----------------------------------------------------------------------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 5.5 V System Supply Input Operation voltage Range VDD 2.7 Under Voltage Lock Out VDD 2.2 Supply Current IDD FB=0.2V, Switch 430 550 uA Shut Down Current IDD VEN < 0.4V 0.1 1 uA Line Regulation VIN : 3.0~4.3V 2.4 2.6 2 V % Oscillator Operation Frequency FOSC Maximum Duty Cycle Feedback Voltage 0.8 1 1.2 93 LP3311S 185 MHz % 200 215 mV MOSFET On Resistance of MOSFET RDS(ON) 0.5 Ω SW Current Limit ILM 1 A VOVP 29 V 5 μA Protection OVP Threshold OVP Sink Current Shut Down Voltage VEN Enable on Voltage VEN LP3311s – 02 Version 2.0 Datasheet May.-2013 0.4 V 1.4 www.lowpowersemi.com V Page 3 of 7 Preliminary Datasheet LP3311S Typical Operating Characteristics LP3311s – 02 Version 2.0 Datasheet May.-2013 www.lowpowersemi.com Page 4 of 7 Preliminary Datasheet LP3311S Applications Information LED Current Control Vin 4.7uH 10uF 1uF The LP3311S regulates the LED current by setting the current sense resistor (R1) connecting to feedback and ground. The internal feedback reference voltage is PWM Vin SW EN OVP 200mV. The LED current can be set from following equation easily. GND FB LP3311S 10R ILED=200mV/R1 In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for R1 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. Inductor Selection According to the Superposition Theorem, as the DC The recommended value of inductor for 2 to 10 voltage increases, the voltage contributed to VFB WLEDs applications are 4.7 to 22µH. Small size and increases and the voltage drop on R2 decreases, i.e. better efficiency are the major concerns for portable the LED current decreases. For example, if the VDC device, such as LP3311S used for mobile phone. The range is from 0V to 2.8V, the selection of resistors in inductor should have low core loss at 1MHz and low Figure 4 sets dimming control of LED current from DCR for better efficiency. To avoid inductor saturation 20mA to 0mA. current rating should be considered. Vin 4.7uH 10uF Dimming control 1uF Vin SW EN OVP a. Using a PWM Signal to EN Pin For controlling the LED brightness, the LP3311S can perform the dimming control by applying a PWM signal to EN pin. The internal soft-start and wide range dimming GND frequency from 100Hz to 1MHz can FB LP3311S 5K insignificantly reduce audio noise when dimming. The 65K average LED current is proportional to the PWM signal 10R VDC duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of EN pin, c. Using a Filtered PWM signal in order to let the dimming control perform correctly. 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 LP3311s – 02 Version 2.0 Datasheet May.-2013 www.lowpowersemi.com Page 5 of 7 Preliminary Datasheet 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 Vin LP3311S 4.7uH 10uF 1uF Vin SW EN OVP (<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 GND can get different output current. According to the FB LP3311S 5K application circuit of Figure 5, output current is from 10R 24K 20.5mA to 5.5mA by adjusting the PWM duty cycle PWM from 10% to 90%. LP3311s – 02 Version 2.0 Datasheet 200K May.-2013 www.lowpowersemi.com 0.1uF Page 6 of 7 Preliminary Datasheet LP3311S Package Information LP3311s – 02 Version 2.0 Datasheet May.-2013 www.lowpowersemi.com Page 7 of 7