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SGM3735 38v step-up led driver general description the SGM3735 is a versatile constant current led driver with a high efficiency step-up converter architecture. unique technology and high 1.35a current limit allow SGM3735 to drive up to 38v output (10 leds in series). alternatively, SGM3735 can deliver 260ma total current with 3 series leds per string. it can also maximize the current capability while achieving high conversion efficiency. the optimized 1mhz switching frequency results in reduced conduction loss and small external component size. a single wire dimming interface is integrated to adjust the fb voltage in 32 steps, which can overcome audible noise and inrush current issues in normal pwm dimming schemes. various protection features are built into the SGM3735, 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 SGM3735 is available in green tdfn-22-8l 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 (1.35a limit) 2.7v to 5.5v input voltage range high efficiency pwm converter low 200mv feedback voltage 500k ? pull-low resistor on en/set pin single wire dimming interface 38v open led protection 1mhz switching frequency integrated soft-start function less than 1a shutdown current simple, small solution size available in green tdfn-22-8l package -40 to +85 temperature range applications led backlighting mobile phones handheld devices digital photo frames automotive navigation sg micro corp www.sg-micro.com rev. a. 1
38v step-up led driver 2 SGM3735 sg micro corp www.sg-micro.com package/ordering information model package description specified temperature range order number marking information package option SGM3735 tdfn-22-8l -40 to +85 SGM3735ytde8g/tr 3735 xxxx tape and reel, 3000 note: xxxx = date code. absolute maximum ratings input voltage, v in ????????......?.????.-0.3v to 6v high voltage nodes, sw, vout???.????...-0.3v to 40v other pins, fb, en/set?????...???-0.3v to v in + 0.3v package thermal resistance tdfn-22-8l, ja ????..??...?.???..??.?....75 /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.................... ..................... ...................... ............. ......3000v 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.
38v step-up led driver 3 SGM3735 sg micro corp www.sg-micro.com pin configuration (top view) pgnd sw vout fb rset gnd en/set vin tdfn-22-8l 8 7 6 5 1 2 3 4 gnd SGM3735 pin description pin name function 1 pgnd power ground. 2 vin supply input. 3 en/set enable control and single wire dimming interface. drive to a logic high to enable the device. use pulse to dim led brightness. keep en/set pin in "low" status for 3ms to shut down chip. 4 gnd ground. 5 rset rset pin. connect one resistor from rset to gnd to program the maximum white led current. 6 fb feedback input. connect this pin to the cathode of the white led. 7 vout output and over-voltage protection pin. 8 sw switch output. connect this pin to the inductor and the schottky diode. exposed pad gnd exposed pad should be soldered to pcb board and connected to gnd. typical application vin en/set pgnd fb vout d1 c out input range 2.7v~5.5v c in SGM3735 l sw white leds up to 10 in series or up to 10s4p up to 38v output 8 2 1 7 6 3 rset 5 r set 1k gnd 4 brightness control
38v step-up led driver 4 SGM3735 sg micro corp www.sg-micro.com electrical characteristics (1) (v in = 3.6v, l = 10 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 0.72 1.20 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 192 200 212.5 mv 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 1.0 1.35 1.7 a oscillator frequency f s full 0.8 1.0 1.22 mhz maximum duty cycle d max +25 92 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 logic high pulse width timing t high_min +25 0.4 s logic low pulse width timing t low +25 0.4 750 s minimum shutdown pulse width timing t off +25 3 ms junction thermal shutdown threshold 150 junction thermal shutdown hysteresis 15 note: 1. the SGM3735 is guaranteed to meet performance specifications over the -40 to +85 operating temperature range by design, characterization and correlation with statistical process controls.
38v step-up led driver 5 SGM3735 sg micro corp www.sg-micro.com typical performance characteristics t a = +25 , l = 10 h, c in = 10 f, c out = 0.47 f, unless otherwise noted. feedback voltage vs. temperature 185 190 195 200 205 210 215 -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 2.533.544.555.5 input voltage (v) efficiency (%) 10 leds i led = 20ma, l = 10 h efficiency vs. output current 50 60 70 80 90 100 0 5 10 15 20 25 30 output current (ma) efficiency (%) 10 leds v in = 3.6v, l = 10 h feedback voltage vs. input voltage 185 190 195 200 205 210 215 2.5 3 3.5 4 4.5 5 5.5 input voltage (v) feedback voltage (mv) 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 (%) 10 leds i led = 20ma, l = 22 h 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=10 h, 8 leds ac coupled
38v step-up led driver 6 SGM3735 sg micro corp www.sg-micro.com typical performance characteristics t a = +25 , l = 10 h, c in = 10 f, c out = 0.47 f, unless otherwise noted. open led protection time (100 s/div) 200mv/div 10v/div 500ma/div v in = 3.6v, i led = 20ma, l = 10 h, 8 leds v fb v out i l start-up v in = 3.6v, i led = 20ma, l = 10 h, 8 leds 2v/div 10v/div 200ma/div time (400 s/div) v en v out i l
38v step-up led driver 7 SGM3735 sg micro corp www.sg-micro.com function block diagram voltage reference and dimming control pwm control and gate drive thermal shutdown over-voltage protection ramp generator oscillator current limit input logic and dac current sense fb en/set sw vout vin v in current sense SGM3735 500k pull-low resistor v ref led current control rset comp gm pgnd gnd
38v step-up led driver 8 SGM3735 sg micro corp www.sg-micro.com functional description the SGM3735 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 SGM3735 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 SGM3735 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 SGM3735 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. the single wire control interface accepts a series of pulses into the en/set pin to program the reference voltage. the number of rising edges is detected internally and decoded as illustrated in table 1. the register contains 5 bits, yielding 32 different current levels. using the simplest control method, output current can be toggled on and off between i max and 0ma, by pulling the en/set pin high or low. i max is programmed by the resistor connected between fb and gnd. please see led maximum current setting section in this document to determine the proper resistor value. the next level of control is achieved by injecting a series of pulses into the en/set pin to program the reference voltage at 32 levels. the number of rising edges is detected internally and decoded to the current level as illustrated in table 1. the reference voltage levels are evenly spaced among these 32 steps. the first rising edge on the en/set pin takes the current level to maximum of 100% of i max . then the current will be changed with each additional qualified pulse. the current stays unchanged as long as the en/set pin stays high. table 1. current setting data led current ratio data led current ratio data led current ratio data led current ratio 1 32/32 9 24/32 17 16/32 25 8/32 2 31/32 10 23/32 18 15/32 26 7/32 3 30/32 11 22/32 19 14/32 27 6/32 4 29/32 12 21/32 20 13/32 28 5/32 5 28/32 13 20/32 21 12/32 29 4/32 6 27/32 14 19/32 22 11/32 30 3/32 7 26/32 15 18/32 23 10/32 31 2/32 8 25/32 16 17/32 24 9/32 32 1/32
38v step-up led driver 9 SGM3735 sg micro corp www.sg-micro.com application information inductor selection a 6.8 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 cu rrent application (like 10s4p). capacitor selection small size ceramic capacitors are ideal for SGM3735 application. an input capacitor in the range of 1 f to 22 f and a 0.47f output capacitor are suggested for 10/8/6 series led applications. for higher output current applications like 10s4p, larger value output capacitors like 2.2f 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 200mv when the data = 1. the led current is programmed according to the formula i max = 200mv/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 = 200mv/i max table 2. current setting resistor (1% values) r set ( ? ) 1% values i max current (ma) 200 1 40.2 5 20.0 10 13.3 15 10.0 20 6.65 30 2.00 100 vin en/set pgnd fb vout d1 c out 0.47 f input power 2.7v~30v c in 22 f SGM3735 l sw 20ma 10-series white leds 8 2 1 7 3 6 bias voltage 2.7v~5.5v c 1 0.1 f 10 h 1k r set 10 rset 5 gnd 4 brightness control 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)
38v step-up led driver 10 SGM3735 sg micro corp www.sg-micro.com application information current setting at en/set pin current control can be as simple as a bi-level signal at the en/set pin, resulting in leds on at 100% i max or led off state. however, more sophisticated control techniques can be achieved by pulsing the en/set pin. active logic low or high is required since there is no internal pull-up or pull-down at the en/set pin. an example for programming the output current is shown in figure 2. there are two ways to adjust the channels? on/off state or current level. the first way is by simply adding the number of pulses according to table 2. for example, we will use r set = 10 ? to program 20ma i max . in this example, the user can add 12 more pulses when changing from 14/32 (8.75ma when i max = 20ma) to 2/32 (1.25ma when i max = 20ma). however, increasing the current level can be accomplished by two ways, allowing for more flexible programming. since the data in table 1 automatically circles around after 32 pulses, adding 32 - 8 = 24 pulses changes from 6/32 (data 27) to 14/32 (data 19). the second way is to reset the ic by pulling en/set pin low for 3ms (guaranteed shutdown), and then inputting the desired number of pulses. example: going from 6/32 (data 27) to 14/32 (data 19) option 1: send in 24 pulses (19+32-27 = 24); option 2: pull low for 3ms and then send in 19 pulses. 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. please see the SGM3735 evaluation document for detailed pcb layout guidelines. t high > 0.4s en/set i_led 0.4s < t low < 750s t off > 3ms off off 100% 31/32 30/32 4/32 3/32 2/32 1/32 t s = 800s (typ) figure 2. output current programming via en/set pin
38v step-up led driver 11 SGM3735 sg micro corp www.sg-micro.com package outline dimensions tdfn-22-8l recommended land pattern (unit: mm) 0.50 0.24 1.20 0.60 l a1 a2 a n8 n1 n4 k e d1 e1 b e d side view bottom view top view 1.95 0.65 dimensions in millimeters dimensions in inches symbol min max min max a 0.700 0.800 0.028 0.031 a1 0.000 0.050 0.000 0.002 a2 0.203 ref 0.008 ref d 1.900 2.100 0.075 0.083 d1 1.100 1.300 0.043 0.051 e 1.900 2.100 0.075 0.083 e1 0.500 0.700 0.020 0.028 k 0.200 min 0.008 min b 0.180 0.300 0.007 0.012 e 0.500 typ 0.020 typ l 0.250 0.450 0.010 0.018
38v step-up led driver 12 SGM3735 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 tdfn-22-8l 7 9.5 2.30 2.30 1.10 4.00 4.00 2.00 8.00 q1 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
38v step-up led driver 13 SGM3735 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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