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wd3125 high efficiency, 40v step - up white led driver descriptions the wd3125 is a constant current, high efficiency led driver. internal mosfet can drive up to 10 white leds in series and 3s9p leds with 1.2a current limit and 40v ovp. a p ulse - w idth - m odula tion (pwm) signal can be applied to the en pin for led dimming. the device operates with 1mhz fixed switching frequency to reduce output ripple, improve conversion efficiency, and allows to use small external components. the wd3125 is available in sot - 23 - 6l package. standard product is pb - free and halogen - free. features ? input voltage range : 3~5.5v ? open led protection : 4 3 v (typ.) ? reference voltage : 3 00mv ( 5 % ) ? switch ing frequency : 1mhz (typ.) ? efficiency : up to 92% ? m ain switch current limit : 1.2a (typ.) ? pwm dimming frequency : (5khz to200khz) applications ? smart phones ? tablets ? portable games sot - 23 - 6l pin configuration (top view) 3 125 = device code yy = year code ww = week code marking order i nformation device package shipping wd3125 e - 6/tr sot - 23 - 6l 3000/reel&tape 1 2 3 4 5 6 l x g n d f b e n o v p v i n 1 2 3 4 5 6 3125 yyww 1 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 1 2 3 4 5 6 l x g n d f b e n o v p v i n 1 2 3 4 5 6 3125 yyww
typical applications block diagram pin descriptions symbol pin no. descriptions lx 1 switch output gnd 2 ground fb 3 feedback en 4 enable , active high ovp 5 ovp pin, connect to vout vin 6 power supply osc 1 mhz ocp 1 . 2 a pwm logic gate driver current sense ea pwm comp soft start uvlo chip enable lx vin en gnd fb ovp i sense pwm dimming thermal shutdown ovp v ref bandgap reference 6 l 1 10 uh ~ 22 uh rset vin ovp en lx fb gnd vin 5 4 3 2 1 wd 3125 cin 2 . 2 uf cout 50 v / 1 uf vout d 1 wsb 5503 w 10 leds wd3125 2 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification osc 1 mhz ocp 1 . 2 a pwm logic gate driver current sense ea pwm comp soft start uvlo chip enable lx vin en gnd fb ovp i sense pwm dimming thermal shutdown ovp v ref bandgap reference 6 l 1 10 uh ~ 22 uh rset vin ovp en lx fb gnd vin 5 4 3 2 1 wd 3125 cin 2 . 2 uf cout 50 v / 1 uf vout d 1 wsb 5503 w 10 leds
absolute maximum ratings these are stress ratings only. stresses exceeding the range specified under absolute maximum ratings may cause substantial damage to the device. functional operation of this device at other conditions beyond those listed in the specification is not implied and prolonged exposure to extreme conditions may affect device reliability. note 1: surface mounted on fr - 4 board using 1 square inch pad size , dual side , 1oz copper note 2: surface mounted on fr - 4 board using minimum pad size, 1oz copper parameter symbol value unit vin pin voltage r ange v in - 0.3 6.5 v ovp pin voltage r ange v ovp - 0.3 46 v en pin voltage range - - 0.3 v in v lx pin voltage range (dc) - - 0.3 46 v power dissipation C sot - 23 - 6l (note 1) p d 0.5 w power dissipation C sot - 23 - 6l (note 2) 0.3 w junction to ambient thermal resistan ce C sot - 23 - 6l (note 1) r ja 250 o c/w junction to ambient thermal resistance C sot - 23 - 6l (note 2) 416 o c/w junction temperature t j 150 o c lead temperature(soldering, 10s) t l 260 o c operation temperature topr - 40 ~ 85 o c storage temperature tstg - 55 ~ 150 o c wd3125 3 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
electronics characteristics (ta=25 o c, v in =3.7v, v en =v in , c in =c out =1uf, unless otherwise noted) parameter symbol test condition min typ max units operation voltage range v in 3 -- 5.5 v under voltage lockout v uvlo v in rising 1.8 2.2 2.5 v over - voltage threshold v ovp 40 43 46 v uvlo hysteresis v uvlo - hys 0.1 v quiescent current i q no switching 0.3 1 ma supply current i s switching 1 .5 3 ma shutdown current i sd v en < 0.4v 1 a operation frequency f osc 0.8 1 1.2 mhz maximum duty cycle d max 90 92 % pwm dimming clock rate recommended 5 200 khz feedback reference v ref 285 3 00 315 mv on resistance r on i lx =100ma 0. 5 ? current limit i lim 1.2 a en threshold voltage v en l 0.4 v v enh 1.5 v en sink current i en 3 a thermal shutdown temperature t sd 160 c t sd hysteresis t sd - hys 30 c shutdown delay t shdn 1 ms wd3125 4 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
typical characteristics (ta=25 o c, unless otherwise noted) 0 5 10 15 20 25 30 35 40 45 50 50 55 60 65 70 75 80 85 90 95 100 efficency vs. output current efficiency(%) output current(a) 8led vin=3.6v l=22uh vin=4.2v l=22uh vin=5v l=22uh 0 5 10 15 20 25 30 35 40 45 50 50 55 60 65 70 75 80 85 90 95 100 efficency vs. output current efficiency(%) output current(a) 10led vin=3.6v l=22uh vin=4.2v l=22uh vin=5v l=22uh 2.5 3.0 3.5 4.0 4.5 5.0 5.5 20.0 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 21.0 led current vs. supply voltage led current(ma) supply voltage(v) lled=20ma 6led 8led 10led 10 20 30 40 50 60 70 80 90 0 2 4 6 8 10 12 14 16 18 20 led current vs. pwm duty led current(ma) duty(%) 10led f=100k vin=3.6v vin=4.2v vin=5v 1 2 3 4 5 6 7 8 9 10 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 led current vs. pwm duty led current(ma) duty(%) 10led f=100k vin=3.6v vin=4.2v vin=5v 0 20 40 60 80 100 120 140 160 180 200 60 65 70 75 80 85 90 95 100 efficency vs. output current efficiency(%) output current(a) 3x9led vin=3.6v l=10uh vin=4.2v l=10uh vin=5v l=10uh wd3125 5 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 0 5 10 15 20 25 30 35 40 45 50 50 55 60 65 70 75 80 85 90 95 100 efficency vs. output current efficiency(%) output current(a) 8led vin=3.6v l=22uh vin=4.2v l=22uh vin=5v l=22uh 0 5 10 15 20 25 30 35 40 45 50 50 55 60 65 70 75 80 85 90 95 100 efficency vs. output current efficiency(%) output current(a) 10led vin=3.6v l=22uh vin=4.2v l=22uh vin=5v l=22uh 2.5 3.0 3.5 4.0 4.5 5.0 5.5 20.0 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 21.0 led current vs. supply voltage led current(ma) supply voltage(v) lled=20ma 6led 8led 10led 10 20 30 40 50 60 70 80 90 0 2 4 6 8 10 12 14 16 18 20 led current vs. pwm duty led current(ma) duty(%) 10led f=100k vin=3.6v vin=4.2v vin=5v 1 2 3 4 5 6 7 8 9 10 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 led current vs. pwm duty led current(ma) duty(%) 10led f=100k vin=3.6v vin=4.2v vin=5v 0 20 40 60 80 100 120 140 160 180 200 60 65 70 75 80 85 90 95 100 efficency vs. output current efficiency(%) output current(a) 3x9led vin=3.6v l=10uh vin=4.2v l=10uh vin=5v l=10uh
2.5 3.0 3.5 4.0 4.5 5.0 5.5 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 supply current vs. supply voltage supply current(ma) supply voltage(v) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.30 0.31 0.32 0.33 0.34 0.35 quiesscent current vs. supply voltage quiesscent current(ma) supply voltage(v) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 enable threshold voltage vs. supply voltage enable threshold(v) supply voltage(v) rising falling 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.80 0.84 0.88 0.92 0.96 1.00 1.04 1.08 1.12 1.16 1.20 10led iled=20ma frequency vs. supply voltage frequency(mhz) supply voltage(v) -50 -25 0 25 50 75 100 20.0 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 21.0 led current vs. temperature led current(ma) temperature( o c) 10led vin=3.6v vin=4.2v vin=5v -50 -25 0 25 50 75 100 800 850 900 950 1000 1050 1100 frequency vs. temperature frequency(khz) temperature( o c) 10led vin=3.6v vin=4.2v vin=5v wd3125 6 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 2.5 3.0 3.5 4.0 4.5 5.0 5.5 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 supply current vs. supply voltage supply current(ma) supply voltage(v) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.30 0.31 0.32 0.33 0.34 0.35 quiesscent current vs. supply voltage quiesscent current(ma) supply voltage(v) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 enable threshold voltage vs. supply voltage enable threshold(v) supply voltage(v) rising falling 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.80 0.84 0.88 0.92 0.96 1.00 1.04 1.08 1.12 1.16 1.20 10led iled=20ma frequency vs. supply voltage frequency(mhz) supply voltage(v) -50 -25 0 25 50 75 100 20.0 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 21.0 led current vs. temperature led current(ma) temperature( o c) 10led vin=3.6v vin=4.2v vin=5v -50 -25 0 25 50 75 100 800 850 900 950 1000 1050 1100 frequency vs. temperature frequency(khz) temperature( o c) 10led vin=3.6v vin=4.2v vin=5v
start - up from en shutdown from en switching waveform pwm dimming wd3125 7 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
operation information normal operation the wd3125 is a high efficiency, high output voltage boost converter . t he device is ideal for driving white led . the led connection provides even illumination by sour cing the same output current through all leds . the device integrates 40v/ 1.2 a switch fet and operates in pulse width modulation (pwm) with 1m hz fixed switching frequency. t he beginning of each cycle turns on the power mosfet. a slope compensation ramp is a dded to 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 ( ea ), the power mosfet is turned off. the fb voltage can be regulated to the reference voltage of bandgap with ea block . the feedback loop regulates the fb pin to a low reference voltage ( 3 00mv typical), reducing the power dissipation in the current sense resistor. soft - start the wd3125 build - in soft - start function limits inrush c urrent while the device turn - on. cycle - by - cycle current limit the wd3125 uses a cycle - by - cycle current limit circuitry to limit the inductor peak current in the event of an overload condition. the current flow through inductor in charging phase is detect ed by a current sensing circuit. as the value comes across the current limiting threshold t he n - mosfet turns off , so that the inductor will be forced to leave charging stage and enter in discharging stage. therefore, the inductor current will not increase over the current limiting threshold . over - voltage - protection (ovp) the over voltage protection is detected by ovp block , prevent s ic damage as the result of white led disconnection. once output voltage goes over the ovp threshold , lx pin stops switching and the n - mosfet will be turned off. then, the output voltage will be clamped to be near ovp. until the ovp eliminate the n - mosfet will be turned on. uvlo protection to avoid malfunction of the wd3125 at low input voltages, an under voltage lockout is inc luded that disables the device, until the input voltage exceeds 2.2v ( typ. ). shutdown mode drive en to gnd to place the wd3125 in shutdown mode. i n shutdown mode, the reference, control circuit , and the main switch turn off. i nput current falls to smaller than 1 a during shutdown mode. over - temperature - protection (otp) as soon as the junction temperature (t j ) exceeds 160 o c (typ.), the wd3125 goes into thermal shutdown. in this mode, the main n - mosfet is turned off until temperature falls below typically 130 o c . then the device starts switching again. wd3125 8 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
application information e xternal component selection for the application circuit depends on the load current requirements . c ertain trade - offs between different performance parameters can also be made. led cu rrent setting the loop of boost structure will keep the fb pin voltage equal to the reference voltage v ref . therefore, when r set connects fb pin and gnd, the current flows from v out through led and r set to gnd will be decided by the current on r set , which is equal to following equation: set set fb led r 300mv r v i ? ? where i led = output current of leds v fb = regulated voltage of fb r set = current sense resistor the output current tolerance depends on the fb accuracy and the current sensor resistor accuracy. dimmi ng control for the brightness dimming control of the wd3125 , the ic provides typically 3 00mv feedback voltage when the en pin is pulled constantly high. however, en pin allows a pwm signal to reduce this regulation voltage by changing the pwm duty cycle to achieve led brightness dimming control. as shown in figure 1, the duty cycle of the pwm signal is used to chop the internal 3 00mv reference voltage. an internal low pass filter is used to filter the pulse signal. and then the reference voltage can be ma de by connecting the output of the filter to the error amplifier for the fb pin voltage regulation. 3 0 0 m v e n v a + - e r r o r a m p l i f i e r c o m p f b figure1 therefore, although a pwm signal is applied for dimming, but only the wled dc current is modulated. this help to eliminate the audible noise which often occurs when the led current is pulsed in replica of the frequency and the duty cycle of pwm control. the minimum dimming frequency is limited by en shutdown delay time. for optimum performance, recommend to select pwm dimming freque ncy in the range of 5khz~200khz, and pwm duty >3%. the en shutdown delay time is set to 1ms . this means the ic needs to be shutdown by pulling the en low for 1 ms. wd3125 9 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification set set fb led r 300mv r v i 3 0 0 m v e n v a + - e r r o r a m p l i f i e r c o m p f b
applications for driving 3s9p leds the wd3125 can drive different wleds topology. f or example, the figure 6 shows the 3 s9p wleds and total current is equal to 18 0ma. the total wleds current can be set by the rset which is equal to following equation. ref total set v i= r boost inductor selection the selection of the indu ctor affects steady state operation as well as transient behavior and loop stability. i nductor values can have 20% tolerance with no current bias. when the inductor current approaches saturation level, its inductance can decrease 20% to 35% from the 0a va lue depending on how the inductor vendor defines saturation current. using an inductor with a smaller inductance value forces discontinuous pwm when the inductor current ramps down to zero before the end of each switching cycle. this reduces the boost conv erters maximum output current, causes large input voltage ripple and reduces efficiency. large inductance value provides much more output current and higher conversion efficiency. the inductor should have low core loss at 1mhz and low dcr for better effic iency. for these reasons, the recommended value of inductor for 10 series wleds applications is from 10h to 22 h. a 22h inductor optimized the efficiency for most application while maintaining low inductor peak to peak ripple. a 4.7 h to 10 h boost induc tor is recommended in 3s9p led application. input capacitor selection connect the input capacitance from v in to the reference ground plane. input capacitance reduces the ac voltage ripple on the input rail by providing a low - impedance path for the switchi ng current of the boost converter. the capacitor in the range of 1f to 10 f / x7r or x5r is recommended for input side. output capacitor selection the output capacitor is mainly selected to meet the requirements for the output ripple and loop stability. t his ripple voltage is related to the capacitors capacitance and its equivalent series resistance (esr). t he recommend ed minim um capacit ors on output is 1u f /50v , x5r or x7r ceramic capacitor. diode selection the rectifier diode supplies current path to the inductor when the internal mosfet is off. use a schottky with low forward voltage to reduce losses. the diode should be rated for a reverse blocking voltage greater than the output voltage used. the average current rating must be greater than the maximum load current expected, and the peak current rating must be greater than the peak inductor current. diode the following requirements: low forward voltage high switching speed : 50ns max. reverse voltage : v out + v f or more rated current : i pk or more 6 l 1 4 . 7 uh ~ 10 uh rset vdd ovp en lx fb . . . gnd vin 5 4 3 2 1 wd 3125 cin 10 uf cout 1 uf vout 3 s 9 p wleds d 1 wsb 5509 l wd3125 10 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification ref total set v i= r 6 l 1 4 . 7 uh ~ 10 uh rset vdd ovp en lx fb . . . gnd vin 5 4 3 2 1 wd 3125 cin 10 uf cout 1 uf vout 3 s 9 p wleds d 1 wsb 5509 l
p cb layout considerations a good circuit board layout aids in extracting the most performance from the wd3125 . p oor circuit layout degrades the output ripple and the electromagnetic interference (emi) or electro - magnetic compatibility (emc) performance. t h e evaluation board layout is optimized for the wd3125 . u se this layout for best performance. i f this layout needs changing, use the following guidelines: 1. use separate analog and power ground planes. c onnect the sensitive analog circuitry (such as voltage d ivider components) to analog ground; connect the power components (such as input and output bypass capacitors) to power ground. c onnect the two ground planes together near the load to reduce the effects of voltage dropped on circuit board traces. locate c in as close to the v in pin as possible, and use separate input bypass capacitors for the analog. 2. route the high current path from c in , through l to the lx and gnd pins as short as possible. 3. keep high current traces as short and as wide as possible. 4. the out put filter of the boost converter is also critical for layout. the diode and output capacitors should be placed to minimize the area of current loop through output C gnd C lx . 5. avoid routing high impedance traces, such as output, near the high current traces a nd components or near the diode node. 6. if high impedance traces are routed near high current and/or the lx node, place a ground plane shield between the traces. wd3125 pcb suggest layout (demo) wd3125 11 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
package outlin e dimensions sot - 23 - 6l symbol dimensions in millimeter dimensions in i nches min. max. min. max. a 1.050 1.250 0.041 0 .049 a1 0.000 0.100 0.000 0 .004 a2 1.050 1.150 0.041 0 .045 b 0.300 0.500 0.012 0 .020 c 0.100 0.200 0.004 0 .008 d 2.820 3.020 0.111 0 .119 e 1.500 1.700 0.059 0 .067 e1 2.650 2.950 0.104 0 .116 e 0.950 (typ.) 0.037(typ.) e1 1.800 2.000 0.071 0 .079 l 0.300 0.600 0.012 0 .024 0 8 0 8 wd3125 12 of 12 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification

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