preliminary datasheet LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 1 of 9 high performance, constant current switching regulator for 8pcs white led in series general description the LP3382 is a 1.2mhz pwm boost switching regulator designed for constant- current white led driver applications. the LP3382 can drive a string of up to 8 white leds in series, ensuring uniform brightness and eliminating several ballast resistors. the LP3382 implements a constant frequency 1.2mhz 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 250 mv, 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 LP3382 f: pb-free package: b6: sot23-6 pin configurations (sot23-6) features high efficiency: 92% 1.2mhzfixed-frequency pwm operation maximum output voltage up to 29v operating range : 2.7v to 5.5v shutdown supply current:<1ua available in sot23-6 package built-in 29v 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 cin 10uf 10uh r1 12 vin r2 100k ss0520 pwm gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 0-200khz marking information part number top marking package LP3382b6f f5 sot23-6 other information please view website: www.lowpowersemi.com.
preliminary datasheet LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 2 of 9 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 LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 3 of 9 typical application circuit + panel LP3382 for 6pcs application circuit LP3382 for 2x7pcs application circuit 2.2uf 12 gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 12 5.1 panel 5.1 2.2uf 2.2uf + 2.2uf panel + LP3382 for 7pcs application circuit 22uh 2.2uf rset + rset 2.2uf 22uh + 2 + + gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 vin 22uh LP3382 for 2x6pcs application circuit vin rset vin + panel vin panel 2.2uf 2.2uf 2.2uf vin + rset 22uh 22uh rset LP3382 for 27pcs application circuit + 2.2uf
preliminary datasheet LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 4 of 9 absolute maximum ratings supply input voltage--------------------------------------------------------------------------------------------------- ? 0.3v to 6.0v sw input voltage --------------------------------------------------------------------------------------------------------- ? 0.3v to 35v 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.) -------------------------------------------------------------------------------------- 28 0c operation temperature range ------------------------------------------------------------------------------ ? 40c to 80c storage temperature range ----------------------------------------------------------------------------------- ? 65c to 150c esd susceptibility hbm(human body mode) ---------------------------------------------------------------------------------------- 4kv mm((machine mode)) -------------------------------------------------------------------------------------------- 200v 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 2.4 v supply current i dd fb=0.2v, switch 90 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 1.2 mhz maximum duty cycle 93 % feedback voltage LP3382 235 250 265 mv mosfet on resistance of mosfet r ds(on) 0.3 sw current limit ilm 2 a protection ovp threshold v ovp 29 v ovp sink current 5 a shut down voltage v en 0.4 v enable on voltage v en 0.7 v minimum en dimming threshold vfb=0 v 0.7 v minimum en dimming threshold vfb=250mv 1.4 v pwm en dimming range 100 200k hz
preliminary datasheet LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 5 of 9 typical operating characteristics
preliminary datasheet LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 6 of 9 applications information led current control the LP3382 regulates the led current by setting the current sense resistor (r1) connecting to feedback and ground. the internal feedback reference voltage is 250mv. the led current can be set from following equation easily. iled=250mv/r1 in order to have an accurate led current, precision resistors are preferred (1% is recommended). the table for r1 selection is shown below. power sequence in order to assure the normal soft start function for suppressing the inrush cu rrent the input voltage should be ready before en pulls high. soft-start the function of soft-start is made for suppressing the inrush current to an acceptable value at the beginning of power-on. the LP3382 provides a built-in soft-start function by clamping the output voltage of error amplifier so that the duty cycle of the pwm will be increased gradually in the soft-start period. current limiting the current flow through inductor as charging period is detected by a current sensing circuit. as the value comes across the current limiting threshold, the n-mosfet will be turned off so that the inductor will be forced to leave charging stage and enter discharging stage. therefore, the inductor current will not increase over the current limiting threshold. ovp/uvlo/otp the over voltage protection is detected by a junction breakdown detecting circuit. once vout goes over the detecting voltage, lx pin stops switching and the power n-mosfet will be turned off. then, the vout will be clamped to be near vovp. as the output voltage is higher than a specified value or input voltage is lower than a specified value, the chip will enter protection mode to prevent abnormal function. as the die temperature is higher then 160 , the chip also will enter protection mode. th e power mosfet will be turned off during protection mode to prevent abnormal operation. inductor selection the recommended value of inductor for 2 to 8wleds applications are 4.7 to 22h. small size and better efficiency are the major concerns for portable device, such as LP3382 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. capacitor selection input ceramic capacitor of 2.2uf and output ceramic capacitor of 1uf are recommended for the LP3382 applications for driving 8 series wleds. for better voltage filtering, ceramic capacitors with low esr are recommended. x5r and x7r types are suitable because of their wider voltage and temperature ranges. dimming control a. using a pwm signal to en pin for controlling the led brightness, the LP3382 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 200khz can insignificantly reduce audio noise when dimming. the average led current is proportional to the pwm signal duty cycle. the magnitude of the
preliminary datasheet LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 7 of 9 pwm signal should be higher than the maximum enable voltage of en pin, in order to let the dimming control perform correctly. cout 1uf cin 10uf 10uh r1 12 vin r2 100k ss0520 pwm gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 0-200khz 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. cout 1uf 10uh cin 10uf r1 12 vin vfb=250mv r3 56k r2 6.8k vdc ss0520 r4 100k on/off gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 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 recomended 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%. cout 1uf 10uh cin 10uf vin vfb=250mv r4 100k ss0520 on/off gnd 2 en 4 fb 3 vin 6 lx 1 ovp 5 LP3382 pwm r2 6.8k r1 10 r3 56k r69 100k c3 0.1uf (0-100khz)
preliminary datasheet LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 8 of 9 layout consideration for best performance of the LP3382, the following guidelines must be strictly followed. input and output capacitors should be placed close to the ic and connected to ground plane to reduce noise coupling. the gnd and exposed pad should be connected to a strong ground plane for heat sinking and noise protection. keep the main current traces as possible as short and wide. lx node of dc-dc converter is with high frequency voltage swing. it should be kept at a small area. place the feedback components as close as possible to the ic and keep away from the noisy devices.
preliminary datasheet LP3382 LP3382 C 01 version 1.0 datasheet oct.-2011 www .lowpowersemi.com page 9 of 9 packing information
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