1 rev.1.1 parameter symbol limit unit power supply voltage vdd 60 v sw output peak current isw 1 a i/o pin voltage vio gnd-0.3 to vdd+0.3 v power dissipation pd 450 mw operating ambient temperature top -40 to +125 c storage temperature tstg -55 to +150 c elm915b a 54v 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 6 - ? linear or pwm dimming ? soft-start function ? cycle by cycle current limit ? constant off time control ? off time period programmable ? thermal shutdown protection ? internal nmos switch : 54v, 1a ? high ef?ciency : max.90% ? wide input voltage range : 6v to 54v ? package : sot-26 ELM915BA is constant current led driver with fixed off time, which consists of internal switching that can drive 1a peak current and capable of driving single or multiple leds in series connection efficiently. ELM915BA consists of switch nmos transistor (max.1a current) can operate from 6v to 54v. the low-side current detection circuit which is able to set the average current of output by output nmos switch and external resistors is also included in ELM915BA. ELM915BA can be used as buck type and buck-boost type as well. through input of external control signal to ld/pwm pin, ELM915BA is capable of adjusting the value of output current. the ld/pwm is able to control the continuous output current which is from dc level input and the digital one which is from pwm input. the ld/pwm is also equipped with 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. ELM915BA-s symbol a package b: sot-26 b product version a c taping direction s: refer to pkg file ELM915BA - s a b c selection guide
2 rev.1.1 sot-26(top view) 1 2 3 6 5 4 pin configuration 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 vdd power input 6 sw internal switch drain standard 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 sot-26 a to e : assembly lot no. a to z (i, o, x excepted) and 0 to 9 6 - elm915b a 54v 1a switching led driver
3 rev.1.1 block diagram 6 - 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 54v 1a switching led driver parameter symbol condition min. typ. max. unit input dc supply voltage range vdd dc supply voltage 6 54 v shut-down mode supply current iin_ sd ld/pwm to gnd, vin=6v 600 a vdd under voltage lockout threshold uvlo vdd rising 5.4 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(100k) toff rt=100k, vin=6v, vcs=0.4v 0.7 s constant off time(500k) toff rt=500k, vin=6v, vcs=0.4v 3.5 s sw switch resistance rsw(on) vin=6v, vcs=0v 0.5 current sense blanking time tblank vld/pwm=vdd, vcs=0.4v 300 ns electrical characteristics top=25 c vin=6v
4 rev.1.1 6 - elm915b a 54v 1a switching led driver application notes 1) setting peak current with external resistor rs ELM915BA uses open loop peak current mode driver with internal power switch; peak current is determined by the value of rs which is connected between cs and gnd. ipk = 0.25/rs (a) 2) setting constant off time period toff rt is used to set the ?xed off time of internal nmos switch . the ?xed off time is determined by the value of the resistor which is connected to rt and gnd. the connection between rt and toffit is shown as following chart. when rt is set to be 100k , toff becomes 700ns. 0.1 1 10 10 100 1000 toff-rt characteristic toff ( ? s) rt (k ? ) 3) dimming function ELM915BA provides two types of dimming function: linear dimming and pwm one. linear dimming activates when dc voltage added to ld/pwm is within the range from 0.25v to 2.5v; the luminance would be 0% under 0.25v, and 100% under 2.5v. for pwm dimming function, ELM915BA is able to adjust the luminance by digital signal when voltage of ld/pwm is under 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 rev.1.1 6 - elm915b a 54v 1a switching led driver the above diagram shows buck topology circuit. a) vin = 12vdc. b) vled = 3.5v led average forward current is 350ma and ripple current range is 20%(280ma~420ma). if constant off time is 700ns, then rt is required to be 100k. 4) buck topology application s b d v d d s w r t g n d c s e l m 9 1 5 . b a l d / p w m c l 3 5 0 m a l e d x 1 o p e n v i n ( d c ) 1 2 v r t r s l e d 100k 17.5 h 0.6 420ma 20% 350ma 280ma toff=0.7 s d = vled / vin = 3.5 / 12 = 0.292, rs = 0.25 / imax. = 0.25 / 420ma = 0.595 i = 140ma = vled / l toff = 3.5 / l 0.7 , l = 3.5 0.7 / 0.14 = 17.5 h the duty would be changed by vin voltage . 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
6 rev.1.1 6 - elm915b a 54v 1a switching led driver 1 led buck topology application characteristics rt=100 k , l=15 h, rs=0.5 rt=470 k , l=100 h, rs=0.5 0 5 10 15 20 25 30 0 50 100 150 200 250 vin vs iin ? average iin(ma) ? average iin(ma) vin (v) iin (ma) 0 10 20 30 100 150 200 250 300 350 vin-average iled ? average iled(ma) ? average iled(ma) vin (v) iled (ma) v d d s w r t g n d c s e l m 9 1 5 . b a l d / p w m l e d 5 0 0 m a m a x . v f = 3 . 8 v r t r s v i n l o p e n 1 0 0 v 1 a iled 220f 60v iin 1 2 1 2
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