Preliminary Datasheet LP3321 High Performance, Constant Current Switching Regulator For 10PCS White LED In Series General Description The LP3321 is a 1.3MHz PWM boost switching regulator designed for constant- current white LED driver applications. The LP3321 can drive a string of up to 10 white LEDs in series, ensuring uniform brightness and eliminating several ballast resistors. The LP3321 implements a constant frequency 1.3MHz 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 195 mV and 300mV, 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. Ordering Information Features High Efficiency: 90% 1.3MHzFixed-Frequency PWM Operation Maximum Output Voltage up to 40V Operating Range : 2.7V to 5.5V Shutdown Supply Current:<1uA Available in TSOT23-5/TSOT23-6 Package Built-in 40V Over Voltage Protection Minimize the External Component RoHS Compliant and 100% Lead (Pb)-Free Applications WLED Backlight driver OLED Backlight driver PDA MID/PTV Typical Application Circuit Vin LP3321 10uH D1 SS14 F: Pb-Free 5 Vin EN GND LP3321 4 FB 3 2 Package: J6: TSOT23-6 J5: TSOT23-5 FB Voltage Default: VFB=195mV A: VFB=300mV Cout 1uF SW 1 Cin 10uF Pin Configurations VFB=195mV R1 10 Marking information Please view website. (TSOT23-5) LP3321 – 01 Vesion 1.1 Datasheet (TSOT23-6) Feb.-2011 www.lowpowersemi.com Page 1 of 9 Preliminary Datasheet LP3321 Functional pin description TSOT-23-5 TSOT-23-6 Pin Name Pin Function 1 1 SW Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track area to reduce EMI. 2 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. 4 EN 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. 5 NC No connected. 6 Vin Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input noise. 3 4 5 3 Function Block Diagram LP3321 – 01 Vesion 1.1 Datasheet Feb.-2011 www.lowpowersemi.com Page 2 of 9 Preliminary Datasheet LP3321 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 6 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 1.0 FOSC Maximum Duty Cycle Feedback Voltage 1.3 1.5 93 MHz % LP3321 185 195 205 mV LP3321A 285 300 315 mV MOSFET On Resistance of MOSFET RDS(ON) 0.5 Ω SW Current Limit ILM 1.4 A VOVP 42 V 5 μA Protection OVP Threshold OVP Sink Current Shut Down Voltage VEN Enable on Voltage VEN Minimum EN Dimming Threshold Minimum EN Dimming Threshold LP3321 – 01 Vesion 1.1 Datasheet V 0.4 0.6 V VFB=0 V 0.7 V VFB=195mV 1.4 V Feb.-2011 www.lowpowersemi.com Page 3 of 9 Preliminary Datasheet LP3321 Typical Operating Characteristics LP3321 – 01 Vesion 1.1 Datasheet Feb.-2011 www.lowpowersemi.com Page 4 of 9 Preliminary Datasheet LP3321 – 01 Vesion 1.1 Datasheet Feb.-2011 www.lowpowersemi.com LP3321 Page 5 of 9 Preliminary Datasheet LP3321 Applications Information Vin 10uH D1 SS14 Cout 1uF 5 Vin SW 1 Cin 10uF LP3321 PWM 4 EN FB 3 2 ILED=195mV/R1 (LP3321) ILED=300mV/R1 (LP3321A) GND LED Current Control The LP3321 regulates the LED current by setting the current sense resistor (R1) connecting to feedback and ground. The internal feedback reference voltage is 195mV or LP3321A is 300mV. The LED current can be set from following equation easily. VFB=195mV In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for R1 selection is shown below. Inductor Selection The recommended value of inductor for 2 to 10 WLEDs applications are 4.7 to 22µH. Small size and better efficiency are the major concerns for portable device, such as LP3321 used for mobile phone. The inductor should have low core loss at 1.3MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Dimming control 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. Vin Feb.-2011 10uH D1 SS14 Cout 1uF 5 Vin SW 1 Cin 10uF EN FB 3 R3 VDC www.lowpowersemi.com 90k VFB=195mV 4 GND LP3321 2 a. Using a PWM Signal to EN Pin For controlling the LED brightness, the LP3321 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. LP3321 – 01 Vesion 1.1 Datasheet R1 10 R2 5k R1 10 Page 6 of 9 Preliminary Datasheet LP3321 – 01 Vesion 1.1 Datasheet Feb.-2011 Vin 10uH D1 SS14 Cout 1uF 5 Vin SW 1 Cin 10uF FB 3 VFB=195mV EN GND LP3321 4 2 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%. LP3321 R2 R3 R4 PWM (0-100KHz) 100K www.lowpowersemi.com 5k R1 10 90k Cout 0.1uF Page 7 of 9 Preliminary Datasheet LP3321 Packing information LP3321 – 01 Vesion 1.1 Datasheet Feb.-2011 www.lowpowersemi.com Page 8 of 9 Preliminary Datasheet LP3321 – 01 Vesion 1.1 Datasheet Feb.-2011 www.lowpowersemi.com LP3321 Page 9 of 9