1 5 - http://www.elm-tech.com r ev.1. 4 parameter symbol limit unit i nput voltage v dd 60 v sw output peak current isw 1 a other i/o pin voltage vio 7 v junction temperature tj +150 c power dissipation pd 450 mw operating ambient temperature top -40 to +85 c storage temperature tstg -55 to +150 c elm915b a 5 0v 1a switching led driver general description features maximum absolute ratings ? mr16 and general lighting ? automotive lighting ? low voltage industrial lighting ? battery charging ? led back lighting ? illuminated signs application ? linear or pwm dimming ? soft-start function ? cycle by cycle current limit ? constant off time control ? off time period programmable ? over temperature protection : 15 5 30 c ? over voltage protection : 53v 5 % ? internal nmos switch : 5 4 v ? nmos with peak current : 1a ? low quiescent current : < 250 a ? high efficiency : max.90% ? wide input voltage range : 6v to 50v ? package : sot-26 elm915ba is capable of driving single or multiple series connected leds efficiently from a voltage source higher than the led voltage. elm915ba is buck and buck-boost controller with internal switching which can stress 1a peak current stress. the controller operating wide input voltage range from 6v to 50v. elm915ba consists of an output switch and a high-side output current sensing circuit that uses an external resistor to set the nominal average output current. through applying an external control signal to the ld/pwm pin, it can adjust the output current to above or below the set value. the ld/pwm pin will accept either a dc voltage or a pwm waveform to provide a continuous or a gated output current. the ld/pwm also provide soft start function to prevent inrush current. the sot-26 small package makes elm915ba suitable for led mr-16 bulb applications. caution: permanent damage to the device may occur when ratings above maximum absolute ones are used. * taping direction is one way. elm 9 15ba - s symbol a package b: sot-26 b product version a c taping d irection s: refer to pkg file elm915ba - s a b c selection guide
2 5 - http://www.elm-tech.com r ev.1. 4 sot - 26 ( top view) 1 2 3 6 5 4 pin con figuration pin no. pin name pin description 1 cs current sense 2 gnd ground 3 rt constant off time setting 4 ld/pwm linear dim/pwm dim 5 v dd power input 6 sw internal switch drain s tandard circuit dimming led1 led2 8 to 24vac vdd ld/ pwm sw gnd cs rt elm915ba rt rs c sbd l marking a b c d e s o t - 2 6 a to e : assembly lot no. a to z (i, o, x ex cepted) and 0 to 9 elm915b a 5 0v 1a switching led driver
3 5 - http://www.elm-tech.com r ev.1. 4 b lock diagram ld/pwm vdd 2 1 6 3 4 5 gnd cs sw rt otp/ovp toff time modulation regulator 5v 250mv 250 25 0.25 2.5 vd(mv) s r q 250mv 5v vin - + - + - + elm915b a 5 0v 1a switching led driver parameter symbol condition min. typ. max. unit input dc supply voltage range v in input voltage 6 5 0 v ld/pwm pull-up current ild 4.5 a shut-down mode supply current iin_ sd ld/pwm to gnd, vin=6v 450 600 750 a vdd under voltage lockout threshold uvlo vdd rising 4.86 5.40 5.94 v uvlo hysteresis uvlo vdd falling 300 mv ld/pwm low disable voltage vsd ld/pwm voltage falling 180 mv ld/pwm linear dimming voltage range vld 0.25 2.50 v current sense pull-in threshold voltage vcs-th vin=6v, top=25 c 238 250 262 mv constant off time (200 k ) toff rt=200k , vin=6v, vcs=0.4v 2.5 s constant off time (820 k ) toff rt=820k , vin=6v, vcs=0.4v 9.0 s sw switch on resist or rsw(on) vin=6v, vcs=0v 0.5 current sense blanking time tblank vld/pwm=vdd, vcs=0.4v 500 ns voltage overvoltage protection ovp 50 53 56 v overheat protection temperature otp 125 155 185 c electrical characteristics top=25 c vin=6.0v
4 5 - http://www.elm-tech.com r ev.1. 4 elm915b a 5 0v 1a switching led driver application notes 1 ) setting peak current with external resistor rs elm915ba is open loop peak current mode driver with internal power switch; which peak current setting by external resistor rs connected between cs and gnd. ipk = 0.25/rs (a) 2) setting constant off time value (toff) the rt pin can set internal power switch of time with period. the time with period is constant when resistor value between rt to gnd is fixed. following diagram is the reference data for setting the off-time. 3 ) dimming function elm915ba is capable of two types of dimming function - linear and pwm dimming . the linear dimming function works by setting the ld/pwm voltage between 0.25v to 2.5v. elm915ba shutdowns once the ld/ pwm voltage is bellow 0.25v . 0 5 t l d / p w m ( v ) p w m 0 0.5 1 1.5 2 2.5 3 0 20 40 60 80 100 120 ld/pwm-luminance ld/pwm (v) luminance (%) ??? ? ? ? ?? ??? ???? ?????????????????????? ????????? ???????
5 5 - http://www.elm-tech.com r ev.1. 4 elm915b a 5 0v 1a switching led driver the above diagram is buck topology circuit. the input and output specifications as following. vin = 12vdc. vled = vo = 3.5v led average current is 350ma, and the current ripple is 20%. if constant off time is 1.2 s, then set rt to 100k. 4 ) buck topology application dimming led1 led2 vin(dc) vdd ld/ pwm sw gnd cs rt elm915ba rt rs l 420ma 20% 350ma 280ma toff= 1.2 s d = vled / vin = 3.5 / 12 = 0.292, rs = 0.25 / imax. = 0.25 / 420ma = 0.595 i = vled / l toff e 140ma 3. 5 / l 1.2 s, l = 3.5 1.2 s / 0.14 = 30 h the duty will change when vin voltage varies . 5 ) buck-boost topology application d i m m i n g 1 2 v d c v i n l e d l e d l e d l e d l e d l e d v d d s w l d p w m e l m 9 1 5 b a g n d c s r t s b d v l d / p w m l e d x 6 rt 100k l 100h rs 0.6 c1 10f 25v c2 10f 25v
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