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preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 1 of 11 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. ordering information LP3302S f:pb-free j6:tsot23-6 b6: sot23-6 pin configurations sot23-6/tsot23-6 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 + 4.7uh + vin LP3302S 2 4 3 6 1 5 gnd en fb vin lx out 1uf 1uf marking information please view website .
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 2 of 11 application circuit + 2.2uf lp3302 for 2x6pcs application circuit vin rset 12 + vin + 4.7uh rset + vin + panel 2.2uf 2.2uf + LP3302S 2 4 3 6 1 5 gnd en fb vin lx out 4.7uh rset 2.2uf rset 4.7uh panel + panel panel 12 2.2uf LP3302S 2 4 3 6 1 5 gnd en fb vin lx out 2 4.7uh 5.1 2.2uf lp3302 for 6pcs application circuit lp3302 for 21pcs application circuit 2.2uf LP3302S 2 4 3 6 1 5 gnd en fb vin lx out 2.2uf rset + 4.7uh 5.1 vin + LP3302S 2 4 3 6 1 5 gnd en fb vin lx out panel LP3302S 2 4 3 6 1 5 gnd en fb vin lx out 2.2uf + 2.2uf vin lp3302 for 2x7pcs application circuit lp3302 for 7pcs application circuit
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 3 of 11 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 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 en chip enable (active high). voltage sensin g input to trigger the function of over voltage protection. note that this pin is high impedance. there should be a pull low 100k resistor connected to gnd when the control signal is floating. 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
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 4 of 11 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, p d @ t a = 25c sot-23-6 -------------------------------------------------------------------------0.455w lead temperature (soldering, 10 sec.) ----------------------------------------------------------------------------------- 260c operation temperature range --------------------------------------------------------------------------------- ? 40c to 80c storage temperature range ----------------------------------------------------------------------------------- ? 65c to 150c electrical characteristics parameter symbol test condition min typ. max units system supply input operation voltage range v dd 2.7 6 v under voltage lock out v dd 2.4 v supply current i dd fb=0v, switching 0.8 1.3 ma shut down current i dd v en < 0.4v 0.1 1 ua line regulation v in : 3.0~4.3v 3 % oscillator operation frequency f osc 0.8 1.1 mhz maximum duty cycle 89 92 96 % dimming frequency 100 100k hz feedback voltage LP3302S 235 250 270 mv mosfet on resistance of mosfet r ds(on) 0.8 protection ovp threshold v ovp 27.5 29 v ovp sink current 5 a ocp 850 ma shut down voltage v en 0.4 v enable voltage v en 1.5 v
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 5 of 11 typical operating characteristics
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 6 of 11
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 7 of 11
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 8 of 11
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 9 of 11 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. inductor selection the recommended value of inductor for 2 to 6 wleds applications are 2.2 to 22h. 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. th e 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. 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. accord ing 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. 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 figu re 5, output current is from 20.5ma to 5.5ma by adjusting the pwm duty cycle from 10% to 90%.
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 10 of 11 packing information
preliminary datasheet LP3302S LP3302S C02 version 1.2 datasheet feb.-2012 www.lowpower semi.com page 11 of 11

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