preliminary datasheet lp33 11 s lp33 1 1 s C 0 2 ve r sion 2 . 0 d atasheet may . - 20 13 www.lowpowersemi.com page 1 of 7 high performance, constant current switching r egulator for 8 pcs white led in series general description the LP3311S is a 1mhz pwm boost switching regulator designed for constant current white led driver applications. the LP3311S can drive a string of up to 8 white led in series, ensuring uniform brightness and eliminating several ballast resistors. the LP3311S implemen ts a constant frequency 1mhz pwm control scheme. the high frequency pwm operation also saves board space by r educing external component size . to improve efficiency, the feedback voltage is set to 200 mv, which reduces the power dissipation in the current s etting 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 LP3311S f: pb - free package: b6: sot23 - 6 pin configurations in en sw ovp fb 1 2 3 4 6 sot - 23 - 6 gnd 5 features ? high efficiency: 90 % ? ? 1mhz fixed - frequency pwm operation ? maximum output voltage up to 29 v ? operating range : 2.7v to 5 .5 v ? s h u t d o w n s u p p l y c u r r e n t : < 1 u a ? ? available in sot23 - 6 p a c k a g e ? ? built - in 29v o v e r v o l t a g e p r o t e c t i o n ? ? minimize the external component ? rohs compliant and 100% lead (pb) - free applications ? ? wled backlight driver ? ? oled backlight driver ? ? pda ? ? mid/ptv typical application circuit 1uf 4.7uh 10uf vin gnd en fb vin sw ovp LP3311S r1
preliminary datasheet lp33 11 s lp33 1 1 s C 0 2 ve r sion 2 . 0 d atasheet may . - 20 13 www.lowpowersemi.com page 2 of 7 functional pin description sot - 23 - 6 pin name pin function 1 s w 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 sensing 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 ovp over voltage pin. 6 vin supply input voltage pin. bypass 1uf capacitor to gnd to reduce the input noise. function block diagram slope 1 mhz obcillator d r i v e r a 1 enable 4 ms delay over voltage ota soft start pwm _ comp . r s q pwm rs 200 mv in out sw fb en gnd
preliminary datasheet lp33 11 s lp33 1 1 s C 0 2 ve r sion 2 . 0 d atasheet may . - 20 13 www.lowpowersemi.com page 3 of 7 absolute maximum ratings supply input voltage --------------------------------------------------------------------------------- - ----------------- ? 0.3v to 6.0 v s w input voltage -------------------------------------------------------------------------------------- - ----------------- ? 0.3v to 4 3 v the other pins ------------------------------------------------------------------------------------------ - --------------- ? 0.3v to 5.5 v power dissipation, p d @ t a = 25c t sot - 23 - 5 /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 vdd 2.7 5 .5 v under voltage lock out vdd 2.2 2. 4 2.6 v supply current idd fb=0 .2 v, switch 430 550 u a shut down current idd ven < 0.4v 0.1 1 ua line regulation vin : 3.0~4.3v 2 % oscillator operation frequency fosc 0 . 8 1 1. 2 mhz maximum duty cycle 93 % feedback voltage LP3311S 1 8 5 200 2 1 5 m v mosfet on resistance of mosfet rds(on) 0. 5 s w current limit ilm 1 a protection ovp threshold vovp 29 v ovp sink current 5 a shut down voltage ven 0.4 v enable on voltage ven 1 . 4 v
preliminary datasheet lp33 11 s lp33 1 1 s C 0 2 ve r sion 2 . 0 d atasheet may . - 20 13 www.lowpowersemi.com page 4 of 7 typical operating characteristics
preliminary datasheet lp33 11 s lp33 1 1 s C 0 2 ve r sion 2 . 0 d atasheet may . - 20 13 www.lowpowersemi.com page 5 of 7 applications information led current control the LP3311S regulates the led current by setting the current sense resistor (r 1 ) connecting to feedback and ground. the interna l feedback reference voltage is 200 m v . the led current can be set from following equation easily. iled= 200 mv/r1 in order to have an accurate led current, precision resistors are preferred (1% is recommended). the table for r 1 selection is shown below. inductor selection the recommended value of inductor for 2 to 10 wleds applications are 4.7 to 22h. small size and better efficiency are the major concerns for portable device, such as LP3311S used for mobile phone. the inductor should have low core loss at 1mhz and low dcr for better efficiency. to avoid inductor satu ration current rating should be considered. dimming control 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 frequency from 100hz to 1 m hz 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 met hod 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. 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 1uf 4.7uh 10uf vin gnd en fb vin sw ovp LP3311S 10r pwm 65k 5k vdc 1uf 4.7uh 10uf vin gnd en fb vin sw ovp LP3311S 10r
preliminary datasheet lp33 11 s lp33 1 1 s C 0 2 ve r sion 2 . 0 d atasheet may . - 20 13 www.lowpowersemi.com page 6 of 7 application circuit is shown in the figure 6. in thi s 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 c an 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%. 24k 200k 5k 0.1uf pwm 1uf 4.7uh 10uf vin gnd en fb vin sw ovp LP3311S 10r
preliminary datasheet lp33 11 s lp33 1 1 s C 0 2 ve r sion 2 . 0 d atasheet may . - 20 13 www.lowpowersemi.com page 7 of 7 pack age i nformation
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