preliminary datasheet LP3311 LP3311 C 00 version 1.0 datasheet feb.-2011 www.lowpowersemi.com p age 1 of 8 high performance, constant current switching regulator for 10pcs white led in series general description the LP3311 is a 1.3mhz pwm boost switching regulator designed for constant- current white led driver applications. the LP3311 can drive a string of up to 10 white leds in series, ensuring uniform brightness and eliminating several ballast resistors. the LP3311 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 LP3311 - ovp voltage 029:29v 042:42v f: pb-free package: b6: sot23-6 fb voltage default: vfb=200mv a: vfb=300mv pin configurations (sot23-6) 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 sot23-6 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 cout 1uf 4.7uh cin 10uf r1 10 vin gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3311 pwm marking information please view website .
preliminary datasheet LP3311 LP3311 C 00 version 1.0 datasheet feb.-2011 www.lowpowersemi.com p age 2 of 8 functional pin description sot-23-6 pin name pin function 1 sw 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
preliminary datasheet LP3311 LP3311 C 00 version 1.0 datasheet feb.-2011 www.lowpowersemi.com p age 3 of 8 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, p d @ t a = 25c tsot-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 s y mbol test condition min typ. max units system supply input operation voltage range v dd 2.7 6 v under voltage lock out v dd 2.2 2.4 2.6 v supply current i dd fb=0.2v, switch 430 550 ua shut down current i dd v en < 0.4v 0.1 1 ua line regulation v in : 3.0~4.3v 2 % oscillator operation frequency f osc 1.0 1.3 1.5 mhz maximum duty cycle 93 % feedback voltage LP3311 185 200 215 mv LP3311a 285 300 315 mv mosfet on resistance of mosfet r ds(on) 0.5 sw current limit ilm 1.4 a protection ovp threshold v ovp LP3311b6f-042 42 v LP3311b6f-029 29 v ovp sink current 5 a shut down voltage v en 0.4 v enable on voltage v en 0.6 v minimum en dimming threshold vfb=0 v 0.7 v minimum en dimming threshold vfb=200mv 1.4 v
preliminary datasheet LP3311 LP3311 C 00 version 1.0 datasheet feb.-2011 www.lowpowersemi.com p age 4 of 8 typical operating characteristics
preliminary datasheet LP3311 LP3311 C 00 version 1.0 datasheet feb.-2011 www.lowpowersemi.com p age 5 of 8
preliminary datasheet LP3311 LP3311 C 00 version 1.0 datasheet feb.-2011 www.lowpowersemi.com p age 6 of 8 applications information led current control the LP3311 regulates the led current by setting the current sense resistor (r1) connecting to feedback and ground. the internal feedback reference voltage is 200mv or LP3311a is 300mv. the led current can be set from following equation easily. iled=200mv/r1 (LP3311) iled=300mv/r1 (LP3311a) 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 2.2 to 22h. small size and better efficiency are the major concerns for portable device, such as LP3311 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 a. using a pwm signal to en pin for controlling the led brightness, the LP3311 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. cout 1uf 4.7uh cin 10uf r1 10 vin gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3311 pwm 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 increa ses 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. cout 1uf 4.7uh cin 10uf r1 10 vin gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 u4 LP3311 vfb=195mv r2 5k r3 90k vdc
preliminary datasheet LP3311 LP3311 C 00 version 1.0 datasheet feb.-2011 www.lowpowersemi.com p age 7 of 8 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%. pwm gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 u4 LP3311 r2 5k vin r1 10 cout 1uf cin 10uf 4.7uh r3 90k r4 100k cout 0.1uf (0-100khz) for larger panel application circuit r1 12 3s13p cout 4.7uf 4.7uh cin 10uf vin gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3311 pwm
preliminary datasheet LP3311 LP3311 C 00 version 1.0 datasheet feb.-2011 www.lowpowersemi.com p age 8 of 8 packing information
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