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SGM3720 pwm dimming, 38v step-up led driver general description the SGM3720 is a versatile constant current led driver with a high efficiency step-up converter architecture. the low-side power mosfet is integrated in the device, significantly shrinking the overall pcb layout area and minimizing the total number of external components. unique technology and high 1.6a current limit allow SGM3720 to drive up to 38v output (10 leds in series). alternatively, SGM3720 can deliver 260ma total current with 3 series leds per string. it can also maximize the current capability while achieving hi gh conversion efficiency. the optimized 600khz switching frequency results in reduced conduction loss and small external component size. digital pwm dimming interface is integrated to adjust led current. the pwm frequency is in the range from 2khz to 60khz. various protection features are built into the SGM3720, including cycle-by-cycle input current limit protection, open led (output over-voltage) protection and thermal shutdown protection. the leakage current in shutdown mode is less than 1a. the SGM3720 is available in green tsot-23-6 package. it operates over an ambient temperature range of -40 to +85 . features wide output range: up to 10 series leds integrated 40v high current switch (1.6a limit) 2.7v to 5.5v input voltage range high efficiency pwm converter low 300mv feedback voltage 500k ? pull-low resistor on ctrl pin 2khz to 60khz pwm dimming frequency 38v open led protection 600khz switching frequency integrated soft-start function less than 1a shutdown current simple, small solution size -40 to +85 temperature range available in green tsot-23-6 package applications led backlighting mobile phones handheld devices digital photo frames automotive navigation rev. a. 1 sg micro corp www.sg-micro.com
pwm dimming, 38v step-up led driver 2 SGM3720 sg micro corp www.sg-micro.com package/ordering information model package description specified temperature range order number marking information package option SGM3720 tsot-23-6 -40 to +85 SGM3720ytn6g/tr smfxx tape and reel, 3000 note: xx = date code. marking information for example: smfaa (2010, january) smf x x date code - year ("a" = 2010, "b" = 2011 ) date code - month ("a" = jan. "b" = feb. "l" = dec.) chip i.d. absolute maximum ratings input voltage, v in ????????.........?.???.-0.3v to 6v high voltage nodes, sw, vout??????.?...-0.3v to 40v other pins, fb, ctrl??????..???.-0.3v to v in + 0.3v package thermal resistance tsot-23-6, ja ????..?????.?????.?....120 /w storage temperature range...?.???.??...-65 to +150 junction temperature??????????????.?.150 operating temperature range...??????....-40 to +85 lead temperature (soldering 10 sec) ???????????????????????...?. 260 esd susceptibility hbm.................... ..................... ....................... ..................4000v mm......................................................................................200v note: stresses beyond those listed under ?absolute maximum ratings? may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the s pecifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. caution this integrated circuit can be damaged by esd if you don?t pay attention to esd protection. sgmicro recommends that all integrated circuits be handled with appropriate precautions. failure to observe proper handling and installation procedures can cause damage. esd damage can range from subtle performance degradation to complete device failure. precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. sgmicro reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. please contact sgmicro sales office to get the latest datasheet.
pwm dimming, 38v step-up led driver 3 SGM3720 sg micro corp www.sg-micro.com pin configuration (top view) sw gnd fb 4 5 6 3 2 1 vin vout ctrl tsot-23-6 SGM3720 pin description pin name function 1 sw converter switching node. 2 gnd ground. 3 fb output feedback pin regulated at 300mv. 4 ctrl control pin of the boost regulator. it is a multi-functional pin which can be used for enable control and digital pwm dimming. 5 vout output and over-voltage protection pin. 6 vin ic supply. connect vin to a supply voltage between 2.7v and 5.5v. typical application vin ctrl gnd fb vout d1 c out input range 2.7v~5.5v c in SGM3720 l sw white leds up to 10 in series or up to 10s4p up to 38v output pwm dimming 1 6 2 5 3 4 1k r set
pwm dimming, 38v step-up led driver 4 SGM3720 sg micro corp www.sg-micro.com electrical characteristics (1) (v in = 3.6v, l = 22 h, c in = 10 f, c out = 0.47 f, full = -40 to +85 , typical values are at t a = +25 , unless otherwise noted.) parameter symbol conditions temp min typ max units ic supply input voltage range v in full 2.7 5.5 v input under-voltage lockout uvlo rising edge +25 2.5 2.6 v uvlo hysteresis v hys +25 0.15 v quiescent current (non switching) v fb = 0.4v +25 0.20 0.35 ma operating current (switching) i q v fb = 0v +25 0.5 0.9 ma vin pin shutdown current i shdn v en = 0v +25 0.1 1 a step-up converter voltage feedback regulation voltage v ref full 289 300 311 mv v ref filter 3db frequency f ref(3db) +25 500 hz voltage feedback input bias current i fb full 0.001 0.3 a nmos on-resistance r ds(on) +25 0.36 0.55 ? sw pin leakage current i sw +25 0.01 1 a peak nmos current limit i lim +25 1.2 1.6 2.0 a oscillator frequency f s full 475 600 725 khz maximum duty cycle d max +25 91 95 % over-voltage threshold v ovp measured at vout pin full 35.5 38 40.5 v start-up time t s +25 800 s control logic low threshold v il full 0.35 v logic high threshold v ih full 1.5 v minimum shutdown pulse width timing t off +25 3 ms junction thermal shutdown threshold 150 junction thermal shutdown hysteresis 15 note: 1. the SGM3720 is guaranteed to meet performance specifications over the -40 to +85 operating temperature range by design, characterization and correlation with statistical process controls.
pwm dimming, 38v step-up led driver 5 SGM3720 sg micro corp www.sg-micro.com typical performance characteristics t a = +25 , l = 22 h, c in = 10 f, c out = 0.47 f, unless otherwise noted. led current vs. duty cycle 0 5 10 15 20 25 0 20406080100 duty cycle (%) led current (ma) f pwm = 2khz v in = 3.6v, i led = 20ma, l = 22 h, 6 leds f pwm = 20khz efficiency vs. output current 50 60 70 80 90 100 0 5 10 15 20 25 30 output current (ma) efficiency (%) 10leds ` v in = 3.6v, l = 22 h oscillator frequency vs. input voltage 510 540 570 600 630 660 690 2.533.544.555.5 input voltage (v) oscillator frequency (khz) feedback voltage vs. temperature 285 290 295 300 305 310 315 -50 -25 0 25 50 75 100 temperature ( ) feedback voltage (mv) v in = 3.6v efficiency vs. input voltage 80 82 84 86 88 90 2.5 3 3.5 4 4.5 5 5.5 input voltage (v) efficiency (%) i led = 20ma v sw v out i l switching waveform 20v/div 200mv/div 200ma/div time (1 s/div) v in = 3.6v, i led = 20ma, l = 22 h, 8 leds ac coupled
pwm dimming, 38v step-up led driver 6 SGM3720 sg micro corp www.sg-micro.com typical performance characteristics t a = +25 , l = 22 h, c in = 10 f, c out = 0.47 f, unless otherwise noted. start-up v in = 3.6v, i led = 20ma, l = 22 h, 8 leds 2v/div 10v/div 500ma/div time (1ms/div) ctrl v out i l time (100 s/div) v in = 3.6v, i led = 20ma, f pwm = 10khz, l = 22 h, 8 leds ac coupled 2v/div 200mv/div 10ma/div pwm v out i led output ripple at pwm dimming open led protection time (100 s/div) 200mv/div 10v/div 500ma/div v in = 3.6v, i led = 20ma, l = 22 h, 8 leds v fb v out i l
pwm dimming, 38v step-up led driver 7 SGM3720 sg micro corp www.sg-micro.com function block diagram voltage reference and pwm dimming control pwm control and gate drive thermal shutdown over-voltage protection ramp generator oscillator current limit input logic and dac current sense fb ctrl gnd sw vout vin v in current sense SGM3720 500k pull-low resistor v ref led current control comp gm
pwm dimming, 38v step-up led driver 8 SGM3720 sg micro corp www.sg-micro.com functional description the SGM3720 uses a constant-frequency current-mode boost converter architecture to control the led current by regulating the feedback voltage. please refer to the functional block diagram above for an explanation of SGM3720 operation. the beginning of each cycle turns on the power mosfet. a slope compensation ramp is added to the output of the current sense amplifier and the result is fed into the positive input of the comparator (comp). when this voltage goes above the output voltage of the error amplifier (gm), the power mosfet is turned off. the voltage at the output of the gm block amplifies the difference between the reference voltage and the feedback voltage (fb), so that fb voltage can be regulated to the reference voltage. the SGM3720 has built-in soft-start to limit the inrush current during start-up and to limit the amount of overshoot on the output. protection features in the SGM3720 include over-voltage protection (ovp), cycle-by-cycle current limit protection and thermal shutdown. ovp protects in the event where an led fails open, which forces the feedback voltage to zero. this causes the boost converter to operate in maximum duty cycle mode, ramping up the output voltage. switching will stop when the output reaches the ovp threshold. the ovp feature protects the ic from damaging itself by exceeding the voltage rating on sw/vout pins. for the brightness dimming control of the SGM3720, the ic provides typically 300mv feedback voltage when the ctrl pin is pulled constantly high. however, ctrl pin allows a pwm signal to reduce this regulation voltage by changing the pwm duty cycle to achieve led brightness dimming control. an internal low pass filter (500hz) is used to filter the pulse signal. the relationship between the duty cycle and fb voltage can be calculated as following equation. v fb = duty 300mv where: duty = duty cycle of the pwm signal 300mv = internal reference voltage
pwm dimming, 38v step-up led driver 9 SGM3720 sg micro corp www.sg-micro.com application information inductor selection a 10 h to 22 h inductor is recommended for 10/8/6 series led applications and 10s4p led applications. if high efficiency is a critical requirement, a low dcr inductor should be selected. the inductor?s saturation current rating should also exceed the peak input current, especially for high load current application (like 10s4p). capacitor selection small size ceramic capacitors are ideal for SGM3720 application. an input capacitor in the range of 1 f to 22 f and a 0.47 f output capacitor are suggested for 10/8/6 series led applications. for higher output current applications like 10s4p, larger value output capacitors like 2.2 f are recommended to minimize output ripple. diode selection the current rating of the schottky diode should exceed the peak current of the boost converter. the voltage rating should also exceed the target output voltage. led maximum current setting led maximum current setting, i max , is determined by the feedback resistor (r set in figure 1). the feedback voltage is internally set at 300mv when the pwm dimming duty cycle = 100%. the led current is programmed according to the formula i max = 300mv/r set . for accurate led current settings, precision 1% resistors are recommended. the formula and table for r set selection are shown below. r set = 300mv/i max table 1. current setting resistor (1% values) r set ( ? ) 1% values i max current (ma) 300 1 60.4 5 30.0 10 20.0 15 15.0 20 10.0 30 3.00 100 layout considerations pcb layout is very important for high frequency switching regulators in order to keep the loop stable and minimize noise. the input capacitor should be very close to the ic to get the best decoupling. the path of the inductor and output capacitor should be kept as short as possible to minimize noise and ringing. 20ma 10-series white leds gnd vout d1 c out 0.47 f SGM3720 l sw 1 2 5 input power 2.7v~30v c in 22 f 22 h r set 15 vin 6 bias voltage 2.7v~5.5v c 1 0.1 f ctrl 4 pwm dimming 1k fb 3 figure 1. application circuit for 10 leds in series with 20ma current (vin can be tied to input power rail if less than 5.5v)
pwm dimming, 38v step-up led driver 10 SGM3720 sg micro corp www.sg-micro.com package outline dimensions tsot-23-6 e e1 e e1 b d a l 0.25 a1 a2 c 0.99 0.95 0.69 recommended land pattern (unit: mm) 2.59 dimensions in millimeters dimensions in inches symbol min max min max a 0.700 0.900 0.028 0.035 a1 0.000 0.100 0.000 0.004 a2 0.700 0.800 0.028 0.031 b 0.350 0.500 0.014 0.020 c 0.080 0.200 0.003 0.008 d 2.820 3.020 0.111 0.119 e 1.600 1.700 0.063 0.067 e1 2.650 2.950 0.104 0.116 e 0.950 bsc 0.037 bsc e1 1.900 bsc 0.075 bsc l 0.300 0.600 0.012 0.024 0 8 0 8
pwm dimming, 38v step-up led driver 11 SGM3720 sg micro corp www.sg-micro.com tape and reel information note: the picture is only for reference. please make the object as the standard. key parameter list of tape and reel package type reel diameter reel width w1 (mm) a0 (mm) b0 (mm) k0 (mm) p0 (mm) p1 (mm) p2 (mm) w (mm) pin1 quadrant tsot-23-6 7 9.5 3.2 3.1 1.1 4.0 4.0 2.0 8.0 q3 reel width (w1) reel diameter reel dimensions tape dimensions direction of feed p2 p0 w p1 a0 k0 b0 q1 q2 q4 q3 q3 q4 q2 q1 q3 q4 q2 q1
pwm dimming, 38v step-up led driver 12 SGM3720 sg micro corp www.sg-micro.com carton box dimensions note: the picture is only for reference. please make the object as the standard. key parameter list of carton box reel type length (mm) width (mm) height (mm) pizza/carton 7 (option) 368 227 224 8 7 442 410 224 18

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