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TK11851L page 1 application manual white led driver step-up dc-dc converter ic TK11851L contents 1 . description 2 2 . features 2 3 . applications 2 4. typical application 2 5. pin configuration 3 6. block diagram 3 7. standard application circuit 4 8. absolute maximum ratings 5 9. electrical characteristics 6 10. test circuit 7 11. typical characteristics 8 12. pin description 11 13. circuit description 12 14. white led application 20 15. package outline 23 16. notes 24 17. offices 24 meeting your needs
TK11851L page 2 white led driver step-up dc-dc converter ic TK11851L 1. description the TK11851L is a pulse skipping step-up dc-dc converter ic designed for white led driver applications with the following built in: a very high current switching transistor (400 ma peak), an inductor current limit detector, a low voltage reference (v ref = 0.515 v), a high speed oscillator, an error comparator, a zener diode for open- circuit protection and an on/off control. the ic works with a very wide operating supply range (2.3 v to 10 v) and the adjustable output voltage can be set as high as 20 v. the device is in the on state when the en pin is pulled to a high level. using the very small TK11851L and a few external components, battery powered systems with lcd displays, such as digital cameras and cellular phones, can be effectively backlit with white leds. the white leds are connected in series and driven at a constant current, resulting in uniform brightness and high efficiency. this ic has an adjustable oscillator, which allows the designer to set the operating frequency by an external capacitor with the output controlled by pulse skipping. the reference voltage is a very low 0.515 v, achieving high efficiency operation with the constant current output. a small coil can be used because the inductor current limit detector circuit limits the peak current (caused by an input voltage increase or the inrush current at start-up) that flows through the coil. the on /off control is built-in and the circuit current can be decreased when the en pin is low (shutdown mode). the white leds can be dimmed by applying a pwm signal to the en (on / off control) pin. with this method, the white led brightness is still controlled by constant current, resulting in constant chromaticity. the built-in zener diode can be used for open-circuit protection in case the output load is disconnected, such as the string of leds opened. the internal zener diode reduces the external component count. the TK11851L can also be used in other applications as a step-up dc-dc converter. the TK11851L is available in the sot23l-8 surface mount package . 2. features ? very high speed adjustable osc (800khz max) ? very wide operating voltage range (2.3 v to 10 v) ? low loss detector (low reference voltage: v ref = 0.515 v) ? internal switching transistor ? open-circuit protection (ovp) ? active high on / off control ? available intensity control using en pin with pwm signal ? low component count ? very small sot23l-8 surface mount package 3. applications ? led backlighting and frontlighting ? led flashlights ? step-up dc-dc converters 4. typical application application circuit (3 leds in series) l: toko part number d412f: 972as-220m d52lc: a914byw-220m efficiency vs. supply voltage efficiency (%) = 100 ? v ou t ? i led /(v in ? i in ) gnd is ext vfb gnd cx vin 2 3 4 6 en vovp vin on/off 7 8 5 1 l 22 h cx 68pf rled 36 ? vled cout 2.2 f iled cin 4.7 f TK11851L d sb07-03c sanyo 50 60 70 80 90 100 23456 supply voltage(v) efficiency (%) d52lc d31fu vout
TK11851L page 3 5. pin configuration pin no. symbol function 1 vin power supply voltage input. 2 is inductor current limit. 3 ext external inductor. 4 vovp open-circuit protection 5 vfb feedback voltage. 6 gnd ground. 7 cx timing capacitor. 8 en enable (on/off) input. 6. block diagram is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r 7 8 1 rsc TK11851L 5 4 osc clk cx 0.86v 0.3v 18v 0.1v 0.3 ? clk 2.3k ? 300k ? 200k ? 200k ? 1k ? is ext vfb gnd cx vin 2 3 4 6 en vovp 7 8 5 1
TK11851L page 4 7. standard application circuit standard application circuit for white led standard application circuit for lcd bias cin: input capacitor cout: output capacitor l: inductor d: schottky diode r led : led current setting resistor c x : osc frequency setting capacitor cin: input capacitor cout: output capacitor l: inductor d: schottky diode r1, r2: output voltage setting resistor cfb: compensation capacitor c x : osc frequency setting capacitor is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r vin gnd on/off 7 8 1 rsc l cx r led v led cout i led cin TK11851L d 5 4 osc clk cx 0.86v 0.3v 0.1v 0.3 ? clk is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r vin gnd on/off 7 8 1 rsc l cx cin TK11851L d 5 4 osc clk cx 0.86v 0.3v 1k ? 0.1v 0.3 ? i load vout cout cfb r2 r1 clk
TK11851L page 5 8. absolute maximum ratings t a =25 c parameter symbol ratings units test conditions supply voltage v in 20 v switch voltage v sw 20 v vovp pin voltage v ovp -0.3 ~ v ovp v vfb pin voltage v fb -0.3 ~ v in v en pin voltage v en -0.3 ~ 20 v switch peak current i sw, peak 400 ma power dissipation p d 400 mw * storage temperature range t stg -55 ~ +150 c operating temperature range t op -30 ~ +85 c maximum frequency f max ~800 khz operating voltage range v op 2.3 ~ 10 v p d must be decreased at the rate of 3.2mw/c for operation above 25c.
TK11851L page 6 9. electrical characteristics v in =3v, is=open, ext=open, v ov p =open, v fb =gnd, c x =300pf, v en =v in , t a =25 c unless otherwise specified value parameter symbol min typ max units conditions oscillator section (c x pin) c x charging current i chg 16 22 30 a v cx =0.1v, v fb =1v c x discharging current i dis 35 49 65 a v cx =1.0v, v fb =1v charge and discharge current ratio i dis /i chg 2.2 c x threshold voltage + v cx , hi g h 810 860 910 mv v cx at i chg =0ua, v fb =1v c x threshold voltage - v cx , low 260 300 340 mv v cx at i dis =0ua, v fb =1v c x oscillation voltage v osc 520 560 600 mv (v cx, high )-(v cx, low ) current limiting comparator section (is pin) inductor current limit i limit 220 260 300 ma note 1 pin 1-2 total resistance r scext 380 440 500 m ? measured between pin 1 and pin 2 internal effective resistance for inductor current limit sense r sc 300 m ? note 2, note 3 output switch section (ext pin) output transistor saturation voltage v sw, sat 0.2 0.4 v v cx =0v, i sw =200ma output transistor off leak current i sw, off 0.01 2 a v fb =1v, v sw =20v feedback comparator section (vfb pin) reference voltage v ref 0.495 0.515 0.535 v vfb pin output current i fbin -2 -0.3 a v fb =0.4v shutdown section (en pin) en input voltage + v en , hi g h 1.2 20 v on mode en input voltage - v en , low 0.3 v shutdown mode en pin input bias current i enin 25 40 a v en =3v open-circuit protection section (vovp pin) open-circuit voltage v ovp 17 18.5 20 v i z =0.5ma vin section (vin pin) low voltage stop v in , low 1.7 2.0 2.3 v high voltage output stop v in , hi g h 11.5 13.5 14.5 v shutdown supply current i in, off 0.01 1 a v en =0.3v quiescent supply current i in, on 1 1.5 2 ma v fb =1v note 1 i limit : the value of current source i l (dc measurement) when the switching operation is stopped by the is comparator. note 2 r sc : guaranteed by the design equation: sc in limit r v 300 3 . 2 v 1 . 0 i ? = note 3 do not connect the output circuit to ground directly, the r sc might be damaged. (excessive current passes through r sc , schottky diode and coil)
TK11851L page 7 10. test circuit test circuit is ext vfb gnd cx vin 2 3 4 5 6 7 8 en v ovp 1 a i v 10 f a i fb v fb a v cx i chg i dis i sw v sw v i z v v ovp a i en v en v i l v is 300pf in in test circuit for efficiency measuremant. (reference only) efficiency: 78%(typ) a cx 300pf iin v in c in 47 v v out c out 47 1 vin 8 en 7 cx 6 gnd 5 vfb 4 vovp 3 ext 2 is 2200p l 100 d 470k 20k i load 15ma 3.5v TK11851L l: 100 h d63lcb (a921cy-101m) toko d: sb07-03c sanyo
TK11851L page 8 11. typical characteristics osc period time vs. c x capacitance v in =v en =3v, v fb =0v osc frequency vs. temperature v in =v en , v fb =0v, c x =100pf 0 2 4 6 8 10 12 14 0 50 100 150 200 250 300 cx capacitance (pf) osc period (ms) 150 170 190 210 230 250 270 290 -30 -10 10 30 50 70 90 temperature (c) osc frequency (khz) maximum duty vs. osc frequency v in =v en =3v, v fb =0v switch current vs. switch saturation voltage v in =v en =3v, v fb =0v, v cx =0v 66 68 70 72 74 76 78 80 82 10 100 1000 osc frequency (khz) maximum duty (%) 0 100 200 300 400 500 600 0 100 200 300 400 500 switch saturation voltage (mv) switching current (ma) inductor current limit vs. supply voltage v en =v in , v fb =0v, v cx =0v pin 1-2 total resistance vs. temperature (v in -v is )/i l , i l =100ma 0 50 100 150 200 250 300 0 1 2 3 4 5 6 7 8 9 10 11 12 supply voltage (v) inductor current limit (ma) 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50 0.52 -30 -10 10 30 50 70 90 t emperature (c) 1-2pin total resistance ( ) ta=-20 c ta=85 c vin=3v vin=10v ta=85 c ta=25 ta=-20 c temperature ( c) temperature ( c) osc period ( s) pin 1-2 total resistance ( ? ) ta=25 c
TK11851L page 9 reference voltage vs. supply voltage v in =v en , v cx =0v reference voltage vs. temperature v in =v en =3v, v cx =0v 510 511 512 513 514 515 516 517 518 519 520 01234567 8910 supply voltage (v) reference voltage (mv) 510 511 512 513 514 515 516 517 518 519 520 -30 -10 10 30 50 70 90 t emperature (c) reference voltage (mv) supply current vs. en input voltage v in =3v, v fb =0v, c x =100pf supply current vs. en input bias current (en pin current force) v in =3v, v fb =0v, c x =100pf 0 1 2 3 4 5 6 7 8 9 10 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 en input voltage (v) supply current (ma) 0 1 2 3 4 5 6 7 8 9 10 012345678910 en input bias current ( a) supply current (ma) en input bias current vs. en input voltage v in =3v, v fb =0v zener diode current vs. open-circuit voltage v in =3v, v fb =0v, v en =0.3v 0 40 80 120 160 200 240 0 2 4 6 8 10 12 14 16 18 20 en input voltage (v) en pin input bias current ( a) 0 100 200 300 400 500 600 0 2 4 6 8 101214161820 open-ciruit voltage (v) zener diode current ( a) ta=85 c ta=25 c ta=-20 c ta=85 c ta=25 c ta=-20 c ta=85 c ta=25 c ta=-20 c temperature ( c) z ener diode current ( ? ) en input bias current ( ? )
TK11851L page 10 open-circuit voltage vs. temperature v in =3v, v en =0.3v, i z =500 a shutdown supply current vs. supply voltage v in =v en , v en =0.3v 17.0 17.5 18.0 18.5 19.0 19.5 20.0 -30 -10 10 30 50 70 90 t emperature (c) open-circuit voltage (v) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 2 4 6 8 10121416 1820 supply voltage (v) quiescent supply current vs. supply voltage v en =v in , v fb =1v, c x =100pf 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 0 2 4 6 8 10 12 14 16 18 20 supply voltage (v) supply current (ma) ta=85 c ta=25 c ta=-20 c temperature ( c) supply current ( ? ) supply voltage (v)
TK11851L page 11 12. pin description pin no. symbol internal equivalent circuit description 1 vin power supply voltage input. 2is 2 1 0.1v 2.3k ? 300k ? rsc 300m ? bonding wire 70m ? bonding wire 70m ? the function of this pin is to limit the inductor current associated with the is comparator. the device contains a sensing resistor referenced as "r sc ". the value of r sc is 0.3 ? (typ). because there is also bonding-wire resistance, it will be approximately 0.44 ? when measured between pin1 and pin 2. 3ext 3 vin this pin is the collector of the internal 20v npn power switch. the switch transistor has a maximum peak current capability of 400ma and a turn-off delay of 0.2 sec. 4 vovp this pin will work as open-circuit protection. connect vovp to output (vout) to avoid generating high voltage at the switch pin during open-circuit conditions. the zener voltage is approximately 18v. 5vfb 5 0.515v 4 1k ? 18v vin feedback input pin this pin is the non-inverting input of the error comparator with the inverting input biased with the internal temperature-compensated 0.515v reference. the input bias current of fb has a typical value of -0.3 a. 6 gnd ground. 7cx 7 vin the oscillator frequency is determined by the external timing capacitor c x and can be set up to 800khz maximum. the timing capacitor is the only component allowed to be connected to this pin. 8en (on/off) 8 200k ? 200k ? vin this is the chip-enable input with a built-in 200k ? pull-down resistor. set the en-pin higher than 1.2v to enable the device. set the en-pin below 0.3v to disable the device.
TK11851L page 12 13. circuit description TK11851L block diagram 13-1. constant-current (charge and discharge type) oscillator. the oscillator operates by charging and discharging the timing capacitor c x . this generates the linear ramp waveform across c x and the internal squarewave signal of the ic. the period time t of the oscillator is determined by the choice of the timing capacitor c x and is set according to the following equation. ) pf ( x sec) ( ) 15 c ( 038 . 0 t + = (1) the oscillator output signal "clk" is a fixed-duty-cycle pulse train, whose on-off time is fixed internally at a ratio of 2.2:1 2 . 2 t t dischg chg (2) the period time of the oscillator is the period of one full cycle of operation. dischg chg t t t + = (3) t 1 f osc = (4) the oscillator frequency can be set up to 800khz. the internal squarewave (clk) is logical high during the t dischg of ramping down and is low during the t chg of ramping up. when clk goes high and the and gate output is low, the switch transistor will be forced off. at the same time, the r-s flip-flop is set to prepare for the next on cycle. when clk goes low, the inverting signal ( clk ) and the output q of the flip-flop enters the and gate; then the and gate output is high and the switch transistor will be on. cx waveform t chg t dischg t internal waveform clk switch tr off switch tr is possible to turn on. is forced figure 1: osc waveforms is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r vin gnd on/off 7 8 1 rsc l cx r led v led cout i led cin TK11851L d 5 4 osc clk cx 0.86v 0.3v 0.1v 0.3 ? clk 2.3k ? 300k ? 200k ? 1k ? 200k ? 18v 0.3v off 1.2v on vout
TK11851L page 13 13-2. inductor current limit the inductor current-limit function associated with the is comparator is accomplished by sensing the inductor current by means of the voltage drop across the internal resistor r sc . the voltage drop across r sc is compared with the equivalent reference voltage of the is comparator (v limit ). if the inductor peak current exceeds the limit, the is comparator output resets the flip-flop and the switch transistor will be forced off. the limited value of the inductor peak current can be expressed as d sat in sc limit limit , lpk t l v v r v i ? + = (5) where v limit : equivalent reference voltage of is comparator. r sc : effective current-sense resistor, which is set to 0.3 ? . v in : supply input voltage. v sat : switch transistor saturation voltage. l : inductor value. t d : turn-off delay of switch transistor, which is 0.2 sec. 1 2 v in l r wire1 r wire2 r sc 0.3 ? i l r s1 2.3k ? r s2 300k ? 0.1v v in is is comp figure 2: schematic of the inductor current limit in the right side of the equation, the 1st term expresses the limitation by the is comparator and the 2nd term is an additional inductor current caused by the turn-off delay of the switch transistor. the internal equivalent reference voltage of the is comparator v limit depends on the supply voltage vin with resistors r s1 and r s2 , and can be written as in limit v 300 3 . 2 v 1 . 0 v ? (6) therefore, the inductor current limitation i limit from the 1st term can be given as ? ? ? ? ? ? ? = = in sc sc limit limit v 300 3 . 2 v 1 . 0 r 1 r v i (7) (as an example, i limit =256ma at v in =3v) when the voltage drop across r sc reaches the v limit , the switch transistor will be forced off, but there is turn-off delay of the switch transistor (t d =0.2 sec); the additional inductor peak current is expressed as the 2nd term of equation (5). as an example t d =0.2 sec, v in =3v, l=22 h, v sat =0.3v ma 30 t l v v i d sat in lpk = ? = ? as a result, the total amount of inductor peak current is limited by equation (5). for example t d =0.2 sec, v in =3.0v, l=22 h, v sat =0.3v i lpk,limit =256ma (1st term)+30ma (2nd term)=286ma the equations (5), (6) and (7) shows that a higher supply voltage vin will reduce the peak inductor current. this function will allow the use of an inductor with a physically smaller inductor core under a wide operating voltage range. when the supply voltage is higher than 13.5v, the is comparator output keeps the flip-flop reset (through the or gate) and the switch transistor will turn- off constantly. v =v 0 0.1 0.2 0.3 0.4 0.5 03691215 supply voltge vin (v) i limit i lpk,limit opmax in,high figure 3: inductor current limit as a function of supply input voltage (r sc =0.3 ? , l=22 h, v sat =0.3v) inductor peak current (a) i lpk,limit
TK11851L page 14 to increase the inductor peak current if it is necessary to get more output power, add the external resistor r scout between pin 1 and pin 2 in parallel with the internal resistor r sc to increase the inductor peak current. then, the inductor current limit can be expressed as d sat in limit scout scext limit , lpk t l v v i r r 1 i ? + ? ? ? ? ? ? ? ? + = (8) where r scext : internal resistor measured pin 1-pin 2. (r scext =r wire1 +r wire2 +r sc =0.44 ?) r scout : external resistor. i limit : defined in equation (7). d sat in t l v v ? ? : defined as the 2nd term in equation (5). as an example r scout =2.2 ? , v in =3.0v, l=22 h v sat =0.3v, t d =0.2 sec i lpk,limit =340ma 1 v in l r wire1 r wire2 r sc 0.3 ? i l r s1 2.3k ? r s2 300k ? 0.1v r scout 2 is comp v in is figure 4: increased inductor current limit with r scout 13-3. en (on/off) set the en pin higher than 1.2v to enable the device. set it below 0.3v to disable the device; that is, shutdown mode. during shutdown, the supply current drops to 1 a or less. the internal 200k ? pull-down resistor ensures the shutdown mode when the en pin remains open. the en pin can be pulled up to 20v, regardless of the supply voltage and output voltage. the relationship between control current (i en ) and en pin voltage (v en ) is en be en down en en r v v r v i ? + = (9) where r down =r en =200k ? , r enout =0 ? if the voltage applied to the en pin is too high, put r enout in series with the en pin to reduce its bias current. r down 200k ? r en 200k ? vin 8 r enout v en en figure 5: internal equivalent circuit of en pin the en pin is also used to provide led-dimming (see dimming). 13-4. operating supply voltage range when the supply voltage falls below 2.0v (v in,low ), the TK11851L stops switching operation to avoid malfunction. the level of v in,low is determined by the internal circuit. when the supply voltage is above 13.5v (v in,high ), the TK11851L also stops switching operation because of the limitation from equation (7). however, the maximum rating for the supply voltage is as high as 20v. figure 6: operating supply voltage range (v en =v in , v fb =0v, c x =100pf) 0 1 2 3 4 5 6 7 8 9 10 0 2 4 6 8 10 12 14 16 18 20 supply voltage (v) supply current (ma) v in , low v in,high
TK11851L page 15 13-5. error comparator, vfb the error comparator section of the circuit compares the output feedback voltage vfb with the 0.515v internal reference and generates a reset signal which inhibits the oscillator output from turning the switch transistor on whenever the output voltage is too high (see block diagram). in this manner, the drive to the switch transistor is essentially an intermittent pulse train, as a result of the pulse skipping operation. this architecture allows the series-connected white leds to be driven with a constant current. the led current (i led ) is set by an external resistor (r led ) connected between the feedback pin and gnd (see figure 7). the current of each led is led ref led r v i = (10) where v ref : the feedback reference voltage 0.515v output voltage vout is given by ref f out v v n v + ? = (11) where v f : led forward voltage drop n : number of leds connected in series the maximum number of leds connected in series (n) is four. v out 5 led r led vref 0.515v 4 cout i led v z =18v vovp vfb r ovp 1k ? figure 7: setting constant current through led to obtain a regulated output voltage for most common step-up regulator applications, connect a voltage divider from the output (vout) to vfb (see figure 8). the regulated output voltage is determined by ? ? ? ? ? ? + = 1 r 2 r 1 v vout ref (12) vout ranges from vin to 16.5v, with open-circuit protection connecting vovp to vout directly. 5 r1 vref 0.515v 4 cout v z =18v vovp r2 vfb v out r ovp 1k ? figure 8: setting output voltage 13-6. open-circuit protection the TK11851L has open-circuit protection by connecting the vovp pin to the output voltage vout. when the main feedback loop is opened, the internal zener diode will work as another path of the feedback loop. this prevents the switch node from generating high voltage. the voltage level at vout is clamped at v out =v ovp =v z +v ref =18.5v where v z =18v zener voltage v ref =0.5v error comparator reference voltage. during open-circuit, the current of zener diode iz is ma 5 . 0 r v r r v i ovp ref led ovp ref z < + = (13) where r ovp =1k ? , r ovp >>r led the clamped level of vout is enough to drive 4 white leds connected in series.
TK11851L page 16 13-7. relationship between supply input voltage and inductor peak current the TK11851L is a pulse skipping step-up dc-dc converter where the inductor peak current is limited by the period time of the oscillator and the inductor current limit circuit. from the equation (1), the period time (t) of the oscillator is ) pf ( x sec) ( ) 15 c ( 038 . 0 t + = (1) also, the switch on time derived from oscillator equation (1) through equation (3) is d d chg on t t 2 . 3 2 . 2 t t t + = + = (14) then, the inductor peak current from the oscillator circuit is written as ) t t 2 . 3 2 . 2 ( l v v i d sat in lpk + ? = (15) this equation (15) shows that when vin increases, i lpk will increase linearly. if i lpk (given by equation (15)) reaches the value of the inductor current limit, the inductor peak current limited by the inductor current limit circuit is expressed as equation (5). d sat in sc limit limit , lpk t l v v r v i ? + = d sat in in sc t l v v v 300 3 . 2 v 1 . 0 r 1 ? + ? ? ? ? ? ? ? = (5) equation (5) shows that when vin increases, i lpk will decrease linearly. as a result, the inductor peak current can be plotted in fig(10) over a wide range of supply voltage input. cx waveform inductor current waveform which is below t t chg t dischg i limit t on t d t d t on i lpk i lpk inductor current waveform which reached limit i limit i i limit figure 9: inductor current waveform supply voltage inductor peak current eqs.(15) ? ? ? ? ? ? + ? = d sat lpk t t 2 . 3 2 . 2 l v v i eqs.(5) ? ? ? ? ? ? ? = in sc lpk,limit v 300 3 . 2 v 1 . 0 r 1 i d sat t l v v ? + in in figure 10: plot of inductor peak current as a function of supply voltage
TK11851L page 17 13-8. dimming the following are 3 kinds of methods. 1. dimming by r led the current of the led (i led ) is determined by r led , which can be set by switches such as transistors. figure 11: example of 3leds with a 4 brightness level circuit the current of the led can be approximated as sw 1 sw 2 i led 1on on r led 1 r led 2 r led 3 v ref 2on off r led 3 r led 1 v ref 3off on r led 3 r led 2 v ref 4off off r led 3 v ref led ref led r v i = r led : total value of resistors v ref =0.515v(typ) is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r vin gnd on/off 7 8 1 rsc l cx v led cout i led cin TK11851L d 5 4 osc clk cx 0.86v 0.3v 0.1v 0.3 ? r led 1 sw1 control signal 1 clk r led 2 control signal 2 sw2 r led 3 13 24 i led brightness level
TK11851L page 18 2. dimming by dac (d/a converter) output dimming is achievable by applying a dac output to the vfb terminal with addition of r dac 1 and r dac 2 figure 11: dimming by dac (d/a converter) output the current of the led can be given as ? ? ? ? ? ? ? ? = ) v v ( r r v r 1 i ref dacout 1 dac 2 dac ref led led where v ref =0.515v(typ) ) v v 2 ( r 1 dacout ref led ? = where r dac1 =r dac2 is assumed i led dac output voltage r dac 2 r dac 1 = v ref = i led r led v ref is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r vin gnd on/off 7 8 1 rsc l cx v led cout i led cin TK11851L d 5 4 osc clk cx 0.86v 0.3v 0.1v 0.3 ? r dac 1 clk r led dac output r dac 2
TK11851L page 19 3. pwm dimming apply the pwm signal to the en terminal; (pin no.8). in this case, a signal frequency of approximately 120 hz is adequate. the average current of the led changes due to the on/off cycle of the ic, which follows the duty cycle of the pwm signal. set the pwm signal at a high level 1.2v and a low level 0.3v, with a driving current over 8 a figure 12: dimming by pwm signal the pwm dimming led current follows the pwm signal. (as shown above) the average led current is obtained from the formula below. 100 duty i i ) max ( led ) avg ( led ? = where led ref ) max ( led r v i = the graph below shows an example with i led max15ma at a duty cycle 80%, 50% and 20%. duty cycle = 80% duty cycle = 50% duty cycle = 20% 10ma/div, 1v/div, 2msec/div 10ma/div, 1v/div, 2msec/div 10ma/div, 1v/div, 2msec/div input pwm signal curve vs. led current curve (ex. three leds, led current 15ma) led current curve vs. pwm signal curve 1.2v 0.3v led current pwm signal (applied to on/off pin.) led setting current ton toff t fdim=1/t=120hz duty(%)=(ton ? 100) / t is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r vin gnd on/off 7 8 1 rsc l cx v led cout i led cin TK11851L d 5 4 osc clk cx 0.86v 0.3v 0.1v 0.3 ? clk r led led current pwm signal led current pwm signal led current pwm signal
TK11851L page 20 14. white led application 14-1. application circuit (3 leds in series) ? led current: 13ma l: 22 h type d412f toko sample number: 972as-220m type d52lc toko sample number a914byw-220m led current and efficiency characteristics efficiency (%)=100 ? v out ? i led /(v in ? i in ) efficiency vs. supply voltage led current vs. supply voltage 50 60 70 80 90 100 23456 supply voltage(v) efficiency (%) 10 12 14 16 18 20 23456 supply voltage(v) led current(ma) d31fb d52lc is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r vin gnd on/off 7 8 1 rsc l 22 h d412f toko cx r led v led cout i led cin TK11851L sb07-03c sanyo 5 4 osc clk cx 0.86v 0.3v 0.1v 0.3 ? 4.7 f 2.2 f clk 68pf 39 ? vout
TK11851L page 21 14-2. application circuit (4 leds in series) ? led current: 13ma l: 15 h type d412f toko sample number: 972as-150m type d52lc toko sample number: a914byw-150m led current and efficiency characteristics efficiency (%)=100 ? v out ? i led /(v in ? i in ) efficiency vs. supply voltage led current vs. supply voltage 50 60 70 80 90 100 23456 supply voltage(v) efficiency (%) 10 12 14 16 18 20 23456 supply voltage(v) led current(ma) is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r vin gnd on/off 7 8 1 rsc l 15 h d412f toko cx r led v led cout i led cin TK11851L sb07-03c sanyo 5 4 osc clk cx 0.86v 0.3v 0.1v 0.3 ? 4.7 f 2.2 f clk 47pf 39? d52lc d31fb vout
TK11851L page 22 14-3. application circuit (10 leds in 2 (5 branches)) ? display backlit current: 13ma key pad current: each branch 4ma l: 22 h type d412f toko sample number: 972as-220m type d52lc toko sample number: a914byw-220m led current and efficiency characteristics efficiency (%)=100 ? v out ? i led /(v in ? i in ) efficiency vs. supply voltage led current vs. supply voltage 50 60 70 80 90 100 23456 supply voltage(v) efficiency (%) 0 5 10 15 23456 supply voltage(v) led current(ma) display backlit current key pad current vout vin gnd on/off l 22 h d412f toko cx 68pf cout 2.2 f cin 4.7 f 39 ? 13ma 4ma for key pad for display backlit r led is ext vfb gnd cx vin 2 3 6 en vovp error comp vref is comp 0.515v band gap reference clk q s r 7 8 1 rsc TK11851L 5 4 osc clk cx 0.86v 0.3v 0.1v 0.3 ? clk sb07-03c sanyo 4ma 4ma 4ma 300? r br 300? r br 300? r br 300? r br d52lc d31fb
TK11851L page 23 15. package outline s0t23l-8 3.3 0.4 2.2 (0.3) 1.2 0.15 0.3 1.0 recommended mount pad 0~0.1 0.1 0.45 1.4max mark 8 5 4 1 0.2 0.1 +0.10 ? 0.05 0.3 0.2 0.8 +0.10 ? 0.05 3.0 0.8 (3.4) 3.5 15max +0.3 ? 0.1 m 0.1
TK11851L gc3-h032a page 24 16. notes ? please be sure that you carefully discuss your planned purchase with our office if you intend to use the products in this application manual under conditions where particularly extreme standards of reliability are required, or if you intend to use products for applications other than those listed in this application manual. z power drive products for automobile, ship or aircraft transport systems; steering and navigation systems, emergency signal communications systems, and any system other than those mentioned above which include electronic sensors, measuring, or display devices, and which could cause major damage to life, limb or property if misused or failure to function. z medical devices for measuring blood pressure, pulse, etc., treatment units such as coronary pacemakers and heat treatment units, and devices such as artificial organs and artificial limb systems which augment physiological functions. z electrical instruments, equipment or systems used in disaster or crime prevention. ? semiconductors, by nature, may fail or malfunction in spite of our devotion to improve product quality and reliability. we urge you to take every possible precaution against physical injuries, fire or other damages which may cause failure of our semiconductor products by taking appropriate measures, including a reasonable safety margin, malfunction preventive practices and fire-proofing when designing your products. ? this application manual is effective from dec. 2001. note that the contents are subject to change or discontinuation without notice. when placing orders, please confirm specifications and delivery condition in writing. ? toko is not responsible for any problems nor for any infringement of third party patents or any other intellectual property rights that may arise from the use or method of use of the products listed in this application manual. moreover, this application manual does not signify that toko agrees implicitly or explicitly to license any patent rights or other intellectual property rights which it holds. ? none of ozone depleting substances(ods) under the montreal protocol is used in manufacturing process of us. 17. offices if you need more information on this product and other toko products, please contact us. ? toko inc. headquarters 1-17, higashi-yukigaya 2-chome, ohta-ku, tokyo, 145-8585, japan tel: +81.3.3727.1161 fax: +81.3.3727.1176 or +81.3.3727.1169 web site: http://www.toko.co.jp/ ? toko america web site: http://www.toko.com/ ? toko europe web site: http://www.tokoeurope.com/ ? toko hong kong web site: http://www.toko.com.hk/ ? toko taiwan web site: http://www.tokohc.com.tw/ ? toko singapore web site: http://www.toko.com.sg/ ? toko seoul web site: http://www.toko.co.kr/ ? toko manila web site: http://www.toko.com.ph/ ? toko brazil web site: http://www.toko.com.br/ meeting your needs to build the quality relied by costomers your distributor

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