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SGM3727 high efficiency, 38v step-up wled driver general description the SGM3727 is a step-up dc/dc converter designed for driving the white leds with an externally programmable constant current. this device features integrated, 38v power mosfet that is capable of driving up to 10 white leds in series, providing inherent current matching for uniform brightness. wled brightness adjustment is easily achieved via a single wire interface, totally 32 brightness levels of led dimming. the SGM3727 features a variety of protection circuits, including integrated over-voltage protection (ovp), soft-start, cycle-by-cycle current limiting, and thermal shutdown protection circuitry. the SGM3727 has 1a current limit. it is available in green tdfn-22-8l package. it operates over an ambient temperature range of -40c to +85c. features high-efficiency boost dc/dc wled bias supply internal 38v, 0.5 ? power mosfet up to 10 serial white leds per string switch current limit: 1a single wire interface 32 brightness levels for led dimming programmable ovp voltage soft-start function no leakage from v in to gnd through led string thermal shutdown cycle-by-cycle over-current protection -40 to +85 operating temperature range available in green tdfn-22-8l package applications tft lcd displays smart phones portable media players gps/personal navigation devices typical application vdd gnd fb ovp sw d1 up to 10 wleds v out r vo2 r vo1 c out v in 2.8v to 5.0v c in rset r s l1 SGM3727 1 2 5 6 7 8 enable and brightness control en/set 3 rev. a. 1 sg micro corp www.sg-micro.com
high efficiency, 38v step-up wled driver 2 SGM3727 sg micro corp www.sg-micro.com package/ordering information model package description specified temperature range order number marking information package option SGM3727 tdfn-22-8l -40 to +85 SGM3727yde8g/tr 3727 xxxx tape and reel, 3000 note: xxxx = date code. absolute maximum ratings sw, fb to gnd........................................................-0.3v to 40v vdd, en/set to gnd................................................-0.3v to 6v rset, ovp to gnd............. ................ ..................... .-0.3v to 6v continuous sw current...........................internally limited to 1a 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.................... ..................... ...................... ............. ......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.
high efficiency, 38v step-up wled driver 3 SGM3727 sg micro corp www.sg-micro.com pin configuration (top view) gnd sw ovp fb rset nc en/set vdd tdfn-22-8l 8 7 6 5 1 2 3 4 gnd SGM3727 pin description pin name function 1 gnd ground. 2 vdd 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 nc no connection. 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 ovp over-voltage protection input. the ic is automatically disabled when the voltage at this pin exceeds 1.24v. connect ovp pin to the center point of a resistive voltage divider connected across the led string. 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.
high efficiency, 38v step-up wled driver 4 SGM3727 sg micro corp www.sg-micro.com electrical characteristics (v in = 3.3v, v en = 2.8v , t a = 25 , unless otherwise specified.) parameter symbol conditions min typ max units input voltage v in 2.8 5.0 v power switch voltage rating 38 v under-voltage lockout threshold v uvlo v in rising 2.1 2.2 2.45 v under-voltage lockout hysteresis 70 mv not switching 0.045 0.08 ma supply current switching 0.12 0.16 ma supply current in shutdown i shdn en/set = gnd 0.2 1 a maximum on time t on v in = 3.5v 5 6.2 7.5 s minimum off time t off 300 420 550 ns rset voltage v rset 300 314 330 mv switch current limit i lim 750 1000 1250 ma switch on resistance r ds(on) v in = 3.3v 0.5 1 ? led switch on resistance v in = 3.3v (from fb to rset) 2.2 ? switch leakage current v sw = 38v, en/set = gnd 0.1 a over-voltage protection threshold v ovp rising 1.1 1.24 1.31 v ovp input current v ovp = 1.5v 1 300 na en/set input current v en = 0v or 2.8v 0.1 1 a thermal shutdown temperature 155 thermal shutdown hysteresis 25 en/set logic en low time for shutdown t shdn 3 ms en low time for dimming t il 0.5 500 s en high time for dimming t ih 0.5 s logic-high voltage v ih 1.5 v en threshold logic-low voltage v il 0.5 v
high efficiency, 38v step-up wled driver 5 SGM3727 sg micro corp www.sg-micro.com typical performance characteristics efficiency vs. led current 50 60 70 80 90 100 0 5 10 15 20 25 30 35 led current (ma) efficiency (%) 10 leds connected c out = 10 f, l = 10 h v in = 5.0v v in = 3.3v v in = 2.8v main switch r ds(on) vs. input voltage 200 300 400 500 600 700 2.5 3 3.5 4 4.5 5 input voltage (v) r ds(on) (m ? ) efficiency vs. input voltage 60 65 70 75 80 85 90 2.533.544.55 input voltage (v) efficiency (%) 10 leds connected i led = 30ma i led = 20ma i led = 10ma quiescent current vs. input voltage 0.02 0.03 0.04 0.05 0.06 0.07 2.5 3 3.5 4 4.5 5 input voltage (v) quiescent current (ma) +25 +85 -40 rset voltage vs. temperature 304 309 314 319 324 329 -50-25 0 255075100 temperature ( ) rset voltage (mv)
high efficiency, 38v step-up wled driver 6 SGM3727 sg micro corp www.sg-micro.com typical performance characteristics
high efficiency, 38v step-up wled driver 7 SGM3727 sg micro corp www.sg-micro.com functional block diagram en/set ovp sw gnd enable circuit thermal shutdown bandgap reference uvlo driver control logic maximum on time minimum off time ov comparator soft-start control fb rset brightness control 0.314v vdd enable
high efficiency, 38v step-up wled driver 8 SGM3727 sg micro corp www.sg-micro.com operation control scheme the SGM3727 uses a minimum off-time, peak current control scheme to achieve excellent performance under high duty-cycle operating conditions. this control scheme initiates a switching cycle only when needed to maintain output voltage regulation, resulting in very high efficiency operation. during each switching cycle, the n-channel power mosfet turns on, increasing the inductor current. the switching cycle terminates when either the inductor current reaches the current limit of 1a or when the cycle lasts longer than the maximum on-time of 6.2 s. once the mosfet turns off, it re mains off for at least the minimum off-time of 420ns, then another switching begins when the error comparator detects that the output is falling out of regulation again. soft-start the SGM3727 limits the in-rush current during start-up by increasing the current limit in two steps starting from i lim /3 for 256 switch cycles to i lim 2/3 for the next 256 switch cycles and then full current limit. see the typical performance characteristics for typical start-up behavior. single wire pulse dimming control the SGM3727 implements a pulse dimming method to control the brightness of white leds. users can easily configure the led current from 1.25ma to 30ma by a serial pulse. the dimming of white leds' current can be achieved by applying a pulse signal to the en/set pin. there are totally 32 current steps could be set by users. the detail operation of brightness dimming is shown in figure 1. shutdown the SGM3727 features low-current shutdown mode. in shutdown mode, the control circuitry is disabled, the leds are disconnected and the quiescent supply current drops to less than 1 a. to disable the SGM3727, simply drive en/set to a logic low for more than 3ms. to enable the ics, drive en/set to a logic high or connect it to the input supply. over-voltage protection the SGM3727 includes internal over-voltage protection circuitry that monitors the ovp pin voltage. over-voltage protection is critical when one of the leds in the led string fails as an open circuit. when this happens, the feedback voltage drops to zero, and the control switches at maximum on time causing the output voltage to keep rising until it exceeds the ma ximum voltage rating of the power mosfet. the SGM3727's over-voltage protection detects this condition and switching ceases if the voltage at the ovp pin reaches 1.24v and stays for about 10s. to set the maximum output voltage, connect a resistor divider from the output node to gnd, with center tap at ovp, and select the two resistors with the following equation: r ov2 = r ov1 ? ? ? ? ? ? ? ? ? ? ? ? ? 1 v 24 . 1 v ovp where v ovp is the over-voltage detection threshold, r ov1 is the resistor between ovp pin and gnd, and r ov2 is the resistor from the output to the ovp pin. as a first estimate, the ovp threshold can often be set to 3.8v times the number of leds in the string. the c out has an effect on the final v ovp . considering the ovp comparator has some delay, the final measured v ovp could be higher than the set v ovp if c out is small. en i ledx shutdown 100% 31/32 30/32 29/32 28/32 3/32 2/32 1/32 31/32 100% shutdown 0 1234529 3101 30 s < t ready 0.5 s < t ih 0.5 s < t il < 500 s 3ms < t shdn figure 1. brightness control by pulse dimming
high efficiency, 38v step-up wled driver 9 SGM3727 sg micro corp www.sg-micro.com application information setting the maximum led current the maximum led current is programmed by appropriate selection of the resistor r s connected between rset pin and gnd. to set the full led current, choose the resistor according to the equation: . rset s led led v 0314 r ii ?? where v rset is the voltage reference and i led is the desired maximum led current, such as 30ma. the current in white led can be adjusted via the en/set single wire interface to provide a simple means of led dimming. inductor selection the SGM3727 was designed for operation with inductors in the 2.2 h to 22 h range. keep in mind that larger-valued inductors (usually requiring higher v in ) generally yield higher efficiency due to lower switching frequency, while smaller inductors typically yield a smaller footprint but at the cost of lower efficiency. for best results, choose an inductor with a low dc-resistance (dcr) and be sure to choose an inductor with a saturation current that exceeds the 1a current limit. diode selection the SGM3727 requires a schottky diode as the rectifier. select a low forward voltage drop schottky diode with forward current (i f ) rating that exceeds the peak current limit of 1a and a peak repetitive reverse voltage (v rrm ) rating that exceeds the maximum output voltage, typically set by the ovp threshold. capacitor selection the SGM3727 only requires a tiny 0.47 f output capacitor for most applications. for better output voltage filtering, a low esr output capacitor is recommended. the selection of the output capacitor value directly influences the output voltage ripple of the converter which also influences line regulation. the ripple can be improved by adding a small feed-forward capacitor from out to fb. 3000pf is a good starting point for most applications. for circuits driving 6 or fewer leds, a 4.7 f input capacitor is generally suitable. for circuits driving more than 6 leds, a 10 f input capacitor may be required. ceramic capacitors are recommended for most applications. for best performance, use x5r and x7r type ceramic capacitors, which possess less degradation in capacitance over voltage and temperature. low input voltage application in applications that have low input voltage range, such as those powered from 2~3 aa cells, the SGM3727 may still be used if there is a suitable system supply (such as 3.3v) available to power the controller. in such an application, the inductor may be connected directly to the battery, while the ic power is supplied by the system supply.
high efficiency, 38v step-up wled driver 10 SGM3727 sg micro corp www.sg-micro.com typical application the SGM3727 can drive different wleds topologies. for example, figure 2 shows the 3 4 wleds configuration. the total wleds current can be set by the r s which is equal to following equation: s rset total r v i ? enable/ brightness control vdd en/set gnd fb ovp sw d1 4 serial wleds v out r vo2 r vo1 c out v in 2.8v to 5.0v c in rset r s l1 SGM3727 1 2 3 5 6 7 8 1 to 3 parallel wleds string figure 2. application for driving 3 4 wleds
high efficiency, 38v step-up wled driver 11 SGM3727 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
high efficiency, 38v step-up wled driver 12 SGM3727 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?? 9.50 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
high efficiency, 38v step-up wled driver 13 SGM3727 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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