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1 publication date: may 2010 sdg00005aeb data sheet part no. package code no. AN30888B ? qfn016-p-0304b
AN30888B 2 sdg00005aeb contents ? overview ????????????????.????????????????????????? 3 ? features ?????????????????????????????????????????. 3 ? applications ????????????????????????????????????????. 3 ? package ?????????????????????????????????????????. 3 ? type ??????????????????????????????????????????? 3 ? application circuit example (block diagram) ?????????????????????????? 4 ? pin descriptions ?????????????????????????????????????? 7 ? absolute maximum ratings ????????????????????????????????? 8 ? operating supply voltage r ange ?????????????????? ????????????.. 8 ? allowable voltage range?????? ???????????? ????????????...???? 9 ? electrical characteristics ??????????????????????????????????. 10 ? electrical characteristics (reference values for design) ?????????????????????. 11 ? control pin mode table ???? ???????????? ???????????? ??????? 12 ? electrical characteristics test procedures ??????????????????????????... 13 ? technical data ?? ?????????.????? ???????...???? ??????????? 16 y i/o block circuit diagrams and pin f unction descriptions ?????????????? ???????. 16 y functions and properties descriptions ??????????????????????.??????. 19 y p d ? t a diagram ?????????????????????????????????????. 29 ? usage notes ????????????..? ??.????????????? ??????????? 30 y special attention and precaution in using ???????????? ?????..?????????? 30
AN30888B 3 sdg00005aeb AN30888B high brightness led driver ic ? overview AN30888B is a boost/buck-boost/buck dcdc controller that drives an external power nmos switch. it is suitable for driving high brig htness led for led lighting applications. ? features y battery operation : 3 v to 15 v y output current range : 0 a to a few amperes depending on rating of external nmos and mode of operation y current mode control architecture y led dimming function availa ble by using pwm signal y 30 mv / 200 mv reference voltage y low standby current y configurable as either boost/b uck-boost/ buck mode converter y built-in various protection circuit : under voltage lock out over voltage protection soft start function ? applications y led lighting module y led lantern applications y white led backlighting for lcd panel y white led flash light driving applications y general led back lighting ? package y 16 pin plastic quad flat non-leaded package (qfn type) ? type y bi?cmos ic
AN30888B 4 sdg00005aeb notes) y this application circuit is an example. the operation of mass production set is not guaranteed. perform enough evaluation and verif ication on the design of mass production set. y use external resistor with 1% accuracy at cs pin. y use ceramic type capacitor (typ. 1 f, min. 0.5 f) at vreg pin. y use schottky diode at vout. y this block diagram is for explaining functions. the part of the block diagram may be omitted, or it may be simplified. ? application circuit example (block diagram) y boost mode ovp gndp v in l d r1 r2 r cs v out i led gnd enb sw cs en uvlo pwm 3.65 v vreg 1.262 v vfb_sel i pk control bgr vreg reference voltage 9 10 2 4 7 6 15 14 12 1 1 f 2.2 f v fb vin
AN30888B 5 sdg00005aeb ? application circuit example (block diagram) (continued) y buck-boost mode ovp gndp v in l d r1 r2 r cs v out i led v fb i pk 2.2 f gnd enb sw cs en uvlo pwm 3.65 v vreg 1.262 v vfb_sel control bgr vreg reference voltage 9 10 2 4 7 6 15 14 12 1 1 f vin notes) y this application circuit is an example. the operation of mass production set is not guaranteed. perform enough evaluation and verif ication on the design of mass production set. y use external resistor with 1% accuracy at cs pin. y use ceramic type capacitor (typ. 1 f, min. 0.5 f) at vreg pin. y use schottky diode at vout. y this block diagram is for explaining functions. the part of the block diagram may be omitted, or it may be simplified.
AN30888B 6 sdg00005aeb ? application circuit example (block diagram) (continued) y buck mode ovp gndp v in gnd enb sw cs en uvlo pwm 3.65 v vreg 1.262 v vfb_sel control bgr vreg reference voltage 9 10 2 4 7 6 15 14 12 1 1 f r cs v fb i pk l d v out i led 2.2 f vin notes) y this application circuit is an example. the operation of mass production set is not guaranteed. perform enough evaluation and verif ication on the design of mass production set. y use external resistor with 1% accuracy at cs pin. y use ceramic type capacitor (typ. 1 f, min. 0.5 f) at vreg pin. y use schottky diode at vout. y this block diagram is for explaining functions. the part of the block diagram may be omitted, or it may be simplified.
AN30888B 7 sdg00005aeb ? pin descriptions ? ? n.c. 16 standby on/off control input enb 12 ? ? n.c. 11 pwm dimming control input pwm 10 external nmos transistor gate drive output sw 9 ? ? n.c. 8 power ground ground gndp 7 over voltage protection input pin for b oost mode; connect to gnd for buck mode input ovp 6 ground ground gnd 15 regulator output output vreg 14 ? ? n.c. 13 ? ? n.c. 5 current sense input cs 4 ? ? n.c. 3 feedback voltage select input vfb_sel 2 power supply of ic power supply vin 1 description type pin name pin no.
AN30888B 8 sdg00005aeb *3 c ?25 to +85 t opr operating ambient temperature 4 ? a ? i gnd gnd pin current 2 *2 mw 100 p d power dissipation 3 notes unit rating symbol parameter a no. *3 c ?55 to +125 t stg storage temperature 5 *1 v 15.5 v dd supply voltage 1 notes) *1 : the values under the condition not exceeding the above absolute maximum ratings and the power dissipation. *2 : the power dissipation shown is the value at t a = 85 c for the independent (unmounted) ic package without a heat sink. when using this ic, refer to the ? p d -t a diagram in the ? technical data and design the heat radiati on with sufficient ma rgin so that the allowable value might not be exceeded based on the conditi ons of power supply voltage, load, and ambient temperature. *3 : except for the power dissipation, operating ambient temp erature, and storage temperature, all ratings are for t a = 25 c. note) absolute maximum ratings are limit values which do not result in damages to this ic, and ic operation is not guaranteed at th ese limit values. ? operating supply voltage range *1 v 3.0 to 12 v in1 supply voltage range (boost mode/buck-boost mode) *1 v 3.0 to 15 v in2 supply voltage range (buck mode) *1 v 3.0 to 15 v in supply voltage range notes unit range symbol parameter note) *1 : the values under the condition not exceeding the above absolute maximum ratings and the power dissipation. ? absolute maximum ratings
AN30888B 9 sdg00005aeb *1 v ?0.3 to v in enb 12 *2 v ?0.3 to 4.3 vreg 14 *2 v ?0.3 to 5.5 pwm 10 *2 v ?0.3 to v reg sw 9 *2 v ?0.3 to v reg ovp 6 *2 v ?0.3 to v reg cs 4 ? v ?0.3 to 5.5 vfb_sel 2 *1 v ?0.3 to 15 vin 1 note unit rating pin name pin no. ? allowable voltage range notes) y allowable current and voltage ranges are limit ranges which do not result in damages to this ic, and ic operation is not guaran teed within these limit ranges. y voltage values, unless otherwise specified, are with respect to gnd. y v in is voltage for vin pin. y do not apply external currents or voltages to any pin not specifically mentioned. notes) *1 : v in must not exceed 15 v. *2 : v reg must not exceed 4.3 v.
AN30888B 10 sdg00005aeb under voltage lock out (uvlo) ? v 2.3 2.1 1.9 v in falling sw off; v reg =no load v uvloon under voltage protection on value 12 ? v 0.5 0.3 0.1 v in rising sw on ? v in falling sw off; v reg =no load v uvlohys under voltage protection hysteresis 13 ? v 0.2 ? ?0.2 sw output low logic; mosfet off condition v swl sw low output logic 11 input pin current consumption ? a 25 ? ? enb = 6 v i enb enable pin current 9 ? ma 1 ? ? enb = v in no load condition i cc operating quiescent current 2 ? v v reg +0.2 ? 0.7 v reg sw output high logic; mosfet on condition v swh sw high output logic 10 ? v 0.3 v reg ? 0 ? v vfbsell vfb_sel low input logic 6 ? v 5 ? 0.7 v reg ? v vfbselh vfb_sel high input logic 5 ? v 0.3 v reg ? 0 ? v pwml pwm low input logic 8 ? a 10 ? ? enb = 0 v i stb standby current 1 ? v 5 ? 0.7 v reg ? v pwmh pwm high input logic 7 ? v 0.3 ? 0 ? v enbl enb low input logic 4 output driver enable (enb), vfb_sel and pwm control function ? v v in ? 3 ? v enbh enb high input logic 3 circuit current consumption limits typ unit max notes min conditions symbol parameter b no. ? electrical characteristics at v in = 6 v, enb = 6 v, pwm = v reg note) t a = 25 c 2 c unless otherwise specified.
AN30888B 11 sdg00005aeb ? mv 40 32 24 vfb_sel = low ovp = 0 v (buck mode) v vfb2 vfb reference voltage 2 ? mv 208 202 196 vfb_sel = high ovp = 0 v (buck mode) v vfb1 vfb reference voltage 1 reference voltage control 14 15 ? v 3.85 3.65 3.45 4v v in 15 v no load condition, cvreg = 1 f v reg vreg output voltage 19 ? % ? 90 ? v in =6v 1 led of v f =3.7v i led = 400 ma vfb_sel = high ovp = 0 v (buck mode) eff efficiency 20 regulator voltage (vreg) ? mhz 1.5 ? ? ? f max maximum operating frequency ? s 2 1 0.5 fix off time at sw pin t off driver off time 17 18 output driver ? v 24 21 18 r1 = 470 k , r2 = 30 k v ovp over voltage protection threshold 16 efficiency over voltage protection (boost mode only) reference values typ unit max notes min conditions symbol parameter b no. ? electrical characteristics (reference values for design) at v in = 6 v note) the characteristics listed below are reference values derive d from the design of the ic and are not guaranteed by inspectio n. if a problem does occur related to these characteris tics, we will respond in good faith to user concerns.
AN30888B 12 sdg00005aeb ? control pin mode table note) see parameters b no. 3, 4, 5, 6, 7 and 8 in the electrical characteristics for control voltage ranges. when pwm is not used, the pin is left floating pwm on pwm off pwm on/off 10 standby / operating mode control operating standby enb on/off 12 pin voltage v fb = 202 mv high feedback voltage selection v fb = 32 mv vfb_sel on/off 2 remarks low description pin no.
AN30888B 13 sdg00005aeb enable (enb), vfb_sel and pwm control function circuit current consumption switch output input parameter c no. 2 3 3 2 2 2 2 s5 1 1 1 1 1 1 1 s6 2 2 2 4 3 2 5 s1 3 1 1 1 1 5 5 s2 2 4 3 2 2 5 5 s3 2 2 2 2 2 2 2 s4 standby current consumption 4 enb = 0 v pwm = 0 v vfb_sel = 0 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 standby current 1 current consumption 4 enb = v in pwm = 0 v vfb_sel = 0 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 operating quiescent current 2 output dc voltage 16 enb = 0.30 v pwm = hi-z vfb_sel = 3.65 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 enb high input logic 3 output dc voltage 16 enb = 3.0 v pwm = hi-z vfb_sel = 3.65 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 enb low input logic 4 output dc voltage / 1mhz 11 enb = v in pwm = hi-z vfb_sel = 0.70 v reg ovp = 0 v cs = 100 mv sw = hi-z 12 10 2 6 4 9 vfb_sel high input logic 5 output dc voltage / 1mhz 11 enb = v in pwm = hi-z vfb_sel = 0.30 v reg ovp = 0 v cs = 100 mv sw = hi-z 12 10 2 6 4 9 vfb_sel low input logic 6 output dc voltage / 1mhz 11 enb = v in pwm = 0.70 v reg vfb_sel = 3.65 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 pwm high input logic 7 pin no. conditions conditions pin no. ? electrical characteristics test procedures
AN30888B 14 sdg00005aeb ? electrical characteristics test procedures (continued) 2 2 2 2 5 2 output dc voltage / 1mhz 11 enb = v in pwm = 0 v vfb_sel = 3.65 v ovp = 0 v cs = 0 v sw = 0 a 12 10 2 6 4 9 sw low output logic 11 output driver input pin current consumption 2 2 2 2 2 2 output dc voltage / 1mhz 11 enb = v in pwm = 3.65 v vfb_sel = 3.65 v ovp = 0 v cs = 0 v sw = 0 a 12 10 2 6 4 9 sw high output logic 10 switch output input parameter c no. 2 2 s5 1 1 s6 2 2 s1 1 4 s2 5 2 s3 2 2 s4 output dc voltage / 1mhz 11 enb = v in pwm = 0.30 v reg vfb_sel = 3.65 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 pwm low input logic 8 current consumption 14 enb = v in pwm = hi-z vfb_sel = 0 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 enable pin current 9 pin no. conditions conditions pin no.
AN30888B 15 sdg00005aeb ? electrical characteristics test procedures (continued) 1 2 2 2 1 2 output dc voltage / 1mhz 11 enb = v in pwm = hi-z vfb_sel = 3.65 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 under voltage protection hysteresis 13 1 2 2 2 1 2 output dc voltage / 1mhz 11 enb = v in pwm = hi-z vfb_sel = 3.65 v ovp = 0 v cs = 0 v sw = hi-z 12 10 2 6 4 9 under voltage protection on value 12 under voltage lock out (uvlo) switch output input parameter c no. s5 s6 s1 s2 s3 s4 pin no. conditions conditions pin no.
AN30888B 16 sdg00005aeb no connection ? ? ? 5 cs current sense pin z : hi-z dc (0 v to 250 mv) 4 ? dc (0 v to 5 v) dc (3 v to 15 v) waveform and voltage vfb_sel feedback voltage select pin z : hi-z 2 no connection ? ? 3 vin power supply of ic z : low ? 1 impedance description internal circuit pin no. 2 200 vfb_sel 14 vreg 4 500 cs 14 vreg ? technical data y i/o block circuit diagrams and pin function descriptions note) the characteristics listed below are reference values derived from the design of the ic and are not guaranteed.
AN30888B 17 sdg00005aeb pwm pwm dimming control z : 170 k pulse (0 v to 5 v) 10 no connection ? ? ? 11 sw external nmos transistor gate driving pulse z : hi-z pulse (0 v to 3.65 v) 9 ? gndp dc (0 v to 1.26 v) waveform and voltage power ground ? ? 7 no connection ? ? 8 ovp over voltage protection input pin for boost and buck-boost mode connect to gnd for buck mode z : hi-z 6 impedance description internal circuit pin no. 6 ovp 14 vreg 1k 1k 9 sw 14 vreg 10 3k pwm 167k v reg v reg ? technical data (continued) y i/o block circuit diagrams and pi n function descriptions (continued) note) the characteristics listed below are reference values derived from the design of the ic and are not guaranteed.
AN30888B 18 sdg00005aeb signal ground ? ? gnd 15 no connection ? ? ? 16 dc (typ. 3.65 v) ? dc (3 v to 15 v) waveform and voltage no connection ? ? 13 vreg regulator output pin z : hi-z 14 enb standby on/off control pin z : 402 k 12 impedance description internal circuit pin no. 12 enb 20k 200k 200k 2k 2k 14 vreg 1 vin 550 550 550 ? technical data (continued) y i/o block circuit diagrams and pi n function descriptions (continued) note) the characteristics listed below are reference values derived from the design of the ic and are not guaranteed.
AN30888B 19 sdg00005aeb (1) overview AN30888B is a constant current led driver. the ic works as a boost /buck-boost/ buck mode dcdc contro ller with external mosfet. operating input voltages ranges from 3 v to 15 v. the mode of oper ation depends on the number of led s to be driven and the supply voltage level. in general, please adhere to the following: if total led voltage drop is more than supply voltage, boost mode is adopted. if led volta ge drop is less than the supply voltage, bu ck mode is adopted . if suppl y voltage is close to the total led voltage drop, the buck-boost mode can be used. please note that th e different mode of operation s hould be manually configured. output led current can be designed ranges from 0 a and to a few am peres depending on the mode of operation, the external mosfet characteristic and feasible r cs value used. the control architecture uses current mode fix off time control. the v fb reference voltage determines led current by setting vf b_sel pin with values of 32 mv or 202 mv under buck mode. by applying v fb voltage of 32 mv, user can achieve higher efficiency with lower power dissipation in r cs resistor. applying 202 mv v fb voltage achieves better led current accuracy. (2) standby enable function AN30888B enters standby mode when enb pin is pulled low. during standby, the ic draw s a small current of value less than 10 a from the power supply. this helps to achieve longer battery us age time. during boost mode ope ration, although external mosfet cannot be turned on at standby condition, there is still a dc cu rrent path between the input and the leds through the inductor an d schottky diode. thus it is important to ma ke sure that during boost mode, the minimum fo rward voltage of the led array must exceed the maximum input voltage to ensure the leds remain off during standby mode. ) n led s * v f v i n ( vout ? ? ? = - - ) * ( n led s v f v i n vout ? = ? technical data (continued) y functions and properties descriptions
AN30888B 20 sdg00005aeb (3) internal regulator an internal 3.65 v regulator is used as the power supply for internal core circuit of this ic. this regulated voltage, v reg will be provided when v in is approximately in the range of 4 v to 15v. for v in lower than 4 v, regulator will act as a v in voltage follower, with out put voltage close to v in. the amount of drop voltage from v in during v in follower mode depends on load current of the regulator and also tolerance of the ic. in general, the regulator output voltage will be approxi mately 0.3 v lower than v in during this mode of operation. this regulator requires a capacitor of 1 f to be connected to vreg pin. this capacitor helps to provide a stable regulated voltage to the ic. the regulator has a current ability of approximately 15 ma. howe ver, it is not designed to provide as external power supply voltage. hence an external load exceeding approximately 0.5 ma to the vreg pin is not allowed. (4) output setting consideration the output voltage, v out is set using the following equations for both boost and buck mode: v out = (v f n leds + v d ) ?????????????????? eq[1] (boost mode) v out = (v in ?v f n leds ) ?????????????????? eq[2] (buck mode) v out = (v f n leds + v d +v in ) ???????????????? eq[3] (buck-boost mode) v in : battery or input power supply voltage v f : led forward drop voltage n leds : number of leds stacked in series v d : schottky diode forward drop voltage for boost mode or buck-boost mode operation, v out setting should be lesser than drain?s ource breakdown voltage of external mosfet as mention in (11). also v out should be lesser than ovp protection threshold as mentioned in (9). for buck mode operation, v out setting should give sufficient voltage for external mosfet to operate properly at the required output current setting. ) n led s * v f v i n ( vout ? ? ? = - - ) * ( n led s v f v i n vout ? = ? technical data (continued) y functions and properties descriptions (continued)
AN30888B 21 sdg00005aeb (5) feedback voltage v fb at cs pin the v fb voltage is generated internally in the ic and output at cs pin. this voltage allows users to fi x the input peak current, i pk as well as the led output current, i led . this voltage will change accord ing to the setting at vfb_sel pin. for operation in boost mode/buck-boost mode, v fb will be inversely proportionally to supply voltage, v in . when input supply voltage decreases, v fb will increase. this ensure led current re main accurate as supply voltage decreases. when operating in buck mode, v fb voltage will remain at 202 mv or 32 mv depending on whether vfb_sel pin is high or low. the following are some figures of v fb voltage with respect to v in . for detail information, please refer to graph and data table information as the following. for boost mode and buck-boost mode : v fb = 116 mv (when vfb_sel = high ; v in =6v) v fb = 50 mv (when vfb_sel = low ; v in =6v) v fb = 198.3 mv (when vfb_sel = low ; v in =3v) v fb = 88 mv (when vfb_sel = low ; v in =3v) for buck mode : v fb = 202 mv (when vfb_sel = high, for all v in level) v fb = 32 mv (when vfb_sel = low, for all v in level) to improve overall efficiency v fb voltage can be set lower by switching vfb_sel = lo w. on the other hand accuracy can be improved by using vfb_sel = high mode. ? technical data (continued) y functions and properties descriptions (continued)
AN30888B 22 sdg00005aeb (5) feedback voltage v fb at cs pin (continued) 32 202 n.a n.a 15 32 32 32 32 32 32 32 32 32 32 32 32 v fb (mv) vfb_sel =low 202 202 202 202 202 202 202 202 202 202 202 202 v fb (mv) vfb_sel = high buck mode n.a n.a 14 n.a n.a 13 26.3 59.0 12 28.3 64.0 11 31.0 70.0 10 34.0 77.3 9 38.0 86.3 8 43.0 98.3 7 50.0 116.0 6 57.7 132.3 5 71.0 161.0 4 88.0 198.3 3 v fb (mv) v fb (mv) v in (v) vfb_sel =low vfb_sel = high boost mode/ buck-boost mode ? technical data (continued) y functions and properties descriptions (continued) boost mode: vcs voltage vs vin 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 357911 vin(v) vcs(mv) vfb_sel="h" vfb_sel="l" buck m ode: vcs voltage vs vin 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 3 5 7 9 11 13 15 vin(v) vcs(mv) vfb_sel="h" vfb_sel="l"
AN30888B 23 sdg00005aeb (6) inductor selection inductor value, l is set by the requi red inductor ripple current desired. the general trend for lower inductor value is a smaller inductor physical size, but a larger input ripple current. similarly, an increase in inductor value will decease input ripple current. users are advice to choose an inductor that can handle the peak current i pk , flowing across it without saturating. in addition, inductor with lower series resistance are preferred to provide better operating efficiency. the following equation gives a general guidelin e in selection inductor value based on 30% peak to peak ripple current across th e inductor. (v out ? v in ) t off l = ????????????? ????????? eq[4] (boost mode buck-boost mode) 0.3 i in (v in ? v out ) t off l = ????????????? ????????? eq[5] (buck mode) 0.3 i led v out = output voltage v in = input supply voltage t off = fixed off time design at 1 s i led = led output current i in is input current from supply voltage please note that the 0.3 factor can be altered if 30% peak to peak current is changed. i.e, if percentage of peak to peak current needed is 40%, this factor will be 0.4. e q[7] - - - - - - - - - - - - - - - l * 2 p k cs i v fb r = - - - - - - - - - - - - p k cs i r = ? technical data (continued) y functions and properties descriptions (continued)
AN30888B 24 sdg00005aeb (7) setting output led current and choosing current sense resistor r cs the led current in this ic can be set easily by selecting the appropriate r cs resistor to be used at cs pin of this chip. for boost mode and buck-boost mode : r cs resistor can be set in the following way : first is to calcul ate input current i in at the required operating condition : i in = (v out + v d ) (i led / v in ) ??????????? eq[6] (boost mode buck-boost mode) v out = output voltage v d = schottky diode forward drop voltage i led = required led current v in = input supply voltage after which the peak input current, i pk can be determine by adding i in with half the peak to peak ripple current at the inductor. (v out ? v in ) t off i pk = i in + ??????????? ???????? eq[7] (boost mode buck-boost mode) 2l t off =t off is fixed off time = 1 s l = inductor value found in part (6) inductor selection v out = output voltage v in = input supply voltage i in = i in is input current found in eq[6] lastly, r cs resistor can be determine by using : v fb r cs = ??? ?????????????????? eq[8] (boost mode buck-boost mode) i pk v fb is voltage at cs pin. refer to data graphs for the v fb voltage at different input voltage condition. i pk is peak current found in eq[7] using numeric example of operating condition : v in =6v, v out =10v, i led = 500 ma, t off =1 s, l = 16 h, v d = 0.4 v, v fb =0.1v@v in =6v from eq[6] : i in = (10 + 0.4) (0.5 / 6) = 0.8667 a (10 ? 6) 1 from eq[7] : i pk = 0.8667 + ??????? = 0.9971 a 2 16 0.1 from eq[8] : r cs = ???? = 100.8 m 0.9917 e q[7] - - - - - - - - - - - - - - - l * 2 p k cs i v fb r = - - - - - - - - - - - - p k cs i r = ? technical data (continued) y functions and properties descriptions (continued)
AN30888B 25 sdg00005aeb (7) setting output led current and choosing current sense resistor r cs (continued) for buck mode : r cs resistor can be set in the following way : first is to calculate the peak current i pk using eq[9]. during buck mode, peak curren t sense correspond to the average output led current plus half of actual current ripple through the inductor. (v in ? v out ) t off i pk = i led + ??????????? ???????? eq[9] (buck mode) 2l v out = output voltage v in = input supply voltage t off =t off = fixed off time design at 1 s i led = led output current l = inductor value found in part (6) inductor selection lastly, r cs resistor can be determine by using : v fb r cs = ??? ?????????????????? eq[10] (buck mode) i pk v fb is voltage at cs pin. refer to data graphs for the v fb voltage at different input voltage condition. i pk is peak current found in eq[9] . using numeric example of operating condition : v in =12v, v out =2v, i led = 500 ma, t off =1 s, l = 66 h, v fb =0.2v (12 ? 2) 1 from eq[9] : i pk = 0.5 + ?????? = 0.575 a 2 66 0.2 from eq[10] : r cs = ???? = 348 m 0.575 please note that for component deviation such as inductor, diodes, etc, these deviation can cause the designed i pk to be higher or lower than the calculated value. users may need to fine tune the value of r cs from the calculated values in order to obtain accurate i led measurement. please take note of total impedance including parasitic impedance of pcb trace at cs pin to ground when designing the required r cs value. this is especially important if the designed i led is high as r cs value will be small and in tu rn making parasitic impedance significant to the total impedance seen at cs pin ? technical data (continued) y functions and properties descriptions (continued)
AN30888B 26 sdg00005aeb (8) soft start soft start circuit is incorporated into this ic to avoid high in-rush current during start-up. after the device is enabled (enb = high), the output inductor curr ent and output voltage will rise slowly from initial condition. this slow start-up time ensure smooth start-up as well as minimize in-rush current. (9) over voltage protection (ovp) when operating in boost mode or buck-boost m ode, over voltage protection is needed to prevent damages to ic or external component damages in cases of open led condition. ovp switches off external power mosfet to prevent output from rising over a designe d ovp voltage. output voltage should be limited to the rating of external component us ed. (for example drain source voltage rating of the exte rnal mosfet or the output capacitor) ovp compares the internal reference voltage of 1. 26 v with output voltage through resistor network. ovp threshold is set using the following equation: 1.262 v (r1 r2) v ovp = ?????????? ???????? eq[11] (boost mode buck-boost mode) r2 if r1 = 470 k , r2 = 30 k , ovp threshold will be designed at around 21 v. when ovp is triggered, output vo ltage will be cl amped at this threshold voltage (with hyst eresis of around 1 v to 2 v) until the f ault (e.g open led condition) has been removed. when operating in buck mode, the ovp pin must be short to ground t o disable this function as ovp function is not necessary in th is mode. ? technical data (continued) y functions and properties descriptions (continued)
AN30888B 27 sdg00005aeb (10) under voltage lock out (uvlo) under voltage lock out prevents ic from opera tion at supply voltage lower than 2.1 v. this function prevent ic from abnormal operation when supply voltage v in drops below our recommended input range. when input voltage is lower than this lock out value of 2.1 v, external mosfet will be switched off. when input voltage rises to 2.4 v or more, device operation starts agai n. this means a hysteresis voltage of about 0.3 v. (11) power mosfet consideration when selecting the power mosfet, it is im portant to consider paramete rs such as gate-source, drain-source breakdown voltage, to tal gate capacitance, on resistance and the drain current rating. when power is turned on for ic operating in boost mode, output vo ltage needed to drive led will be reflected to drain-source vo ltage of the power mosfet. thus it is recommended to select a mosf et that can handle this output vo ltage. alternatively, output and drain-source voltage can be protected and clampe d by ovp circuit as mentioned in point (9). gate capacitance of the mosfet chosen s hould ideally to be smaller than 3 nf. (12) pwm operation pwm signal can be generated externally and input into pwm pin of this ic. this pwm si gnal will turn on and off the output driver , giving an average output led current that is pr oportional to the duty cycle of the pwm signal. i led(avg.) = i led duty??????????????? eq[12] (boost / buck-boost / buck mode) i led(avg.) = the average output led current after pwm is input i led = the nominal led current set in part (7) duty = the ratio of on pulse time compared to total period time of the pwm signal. a pwm frequency of 1 khz or lower is recomme nded to minimize error due to rise an d fall time of the converter output. ? technical data (continued) y functions and properties descriptions (continued)
AN30888B 28 sdg00005aeb (13) maximum duty operation maximum duty limitation is needed when operating in boost or buck- boost mode. this prevents the output voltage from having abnormal operation. for buck mode, there is no need for maximum duty limit as sw pin is able to switch to 100% duty. please refer to the graph below for maximum duty vs v in data for boost and buck-boost mode operation. (14) minimum duty operation parasitic circuit capacitance, inductance an d external mosfet gate drive current can creat e spike in the current sense, cs pin v oltage at the point when external mosfet is switched on. in order to prev ent this spike to terminate the on time prematurely, an internal filter of time constant, 100 ns is designed in chip . this time constant of 100 ns translates to a minimum duty of around 9% for all modes of operation. to further reduce the spike in the cs voltage especially when operating in low i led condition (example: r cs is more than 0.8 or more), external rc filter can be used in between v fb node to cs pin which act as a low pass filter to filter spike noise from entering cs pin. this rc filter time cons tant should be long enough to reduce the para sitic spike without significantly affecti ng the shape of cs voltage. the recommended rc value range from : r = 10 to 1 k and c = 100 pf to 500 pf depending on mode of operation and spike level. 66.33 12.0 v in (v) 69.91 10.0 68.90 10.5 67.97 11.0 71.78 9.0 70.83 9.5 67.09 11.5 72.89 8.5 73.92 8.0 75.19 7.5 76.25 7.0 77.38 6.5 78.40 6.0 79.79 5.5 81.99 5.0 83.58 4.5 85.27 4.0 87.09 3.5 88.73 3.0 duty limit (%) boost/buck-boost mode ? technical data (continued) y functions and properties descriptions (continued)
AN30888B 29 sdg00005aeb ? technical data (continued) y p d ? t a diagram
AN30888B 30 sdg00005aeb y special attention and precaution in using 1. this ic is intended to be used for gene ral electronic equipmen t [led lighting devices]. consult our sales staff in advance for in formation on the foll owing applications: x special applications in which ex ceptional quality and reli ability are required, or if the fail ure or malfunction of this ic may directly jeopardize life or harm the human body. x any applications other than the standard applications intended. (1) space appliance (such as artificial satellite, and rocket) (2) traffic control equipment (such as fo r automobile, airplane, train, and ship) (3) medical equipment for life support (4) submarine transponder (5) control equipment for power plant (6) disaster prevention and security device (7) weapon (8) others : applications of which reliability equivalent to (1) to (7) is required it is to be understood that our company shall not be held respons ible for any damage incurred as a result of or in connection w ith your using the ic described in this book for any special applicatio n, unless our company agrees to your using the ic in this bo ok for any special application. 2. pay attention to the direction of lsi. when mounting it in the wrong direction onto the pcb (printed-circuit-board), it might smoke or ignite. 3. pay attention in the pcb (printed-circuit-board) pattern layout in order to prevent damage due to short circuit between pins. in addition, refer to the pin description for the pin configuration. 4. perform a visual inspection on the pcb be fore applying power, otherwise damage might happen due to problems such as a solder- bridge between the pins of the semiconductor device. also, perfo rm a full technical verification on the assembly quality, becau se the same damage possibly can happen due to conductive substanc es, such as solder ball, that adhere to the lsi during transportation. 5. take notice in the use of this product that it might break or occasionally smoke when an abnormal state occurs such as output pin- vdd short (power supply fault), output pin-gnd short (ground fault), or output-to-output-pin short (load short) . and, safety measures such as an installation of fuses are recommended because the extent of the above-mentioned damage and smoke emission will depend on the current capability of the power supply. 6. when designing your equipment, comply with the range of absolute maximum rating and the guaranteed operating conditions (operating power supply voltage a nd operating environment etc.). esp ecially, please be careful not to exceed the range of absolu te maximum rating on the transient state, such as power-on, power-off and mode -switching. otherwise, we will not be liable for any defect which may arise later in your equipment. even when the products are used within the guaranteed values, ta ke into the consideration of incidence of break down and failur e mode, possible to occur to semiconductor produc ts. measures on the system s such as redundant design, arresting the spread of fi re or preventing glitch are recommended in order to prevent physical injury, fire, social damages, for example, by using the produ cts. 7. when using the lsi for new models, verify the safe ty including the long-term reliability for each product. 8. when the application system is designed by using this lsi, be sure to confirm notes in this book. be sure to read the notes to descriptions and the usage notes in the book. ? usage notes
request for your special attention and precautions in using the technical information and semiconductors described in this book (1) if any of the products or technical information described in this book is to be exported or provided to non-residents, the laws and regulations of the exporting country, especially, those with regard to security export control, must be observed. (2) the technical information described in this book is intended only to show the main characteristics and application circuit examples of the products. no license is granted in and to any intellectual property right or other right owned by panasonic corporation or any other company. therefore, no responsibility is assumed by our company as to the infringement upon any such right owned by any other company which may arise as a result of the use of technical information described in this book. (3) the products described in this book are intended to be used for general applications (such as office equipment, communications equipment, measuring instruments and household appliances), or for specific applications as expressly stated in this book. consult our sales staff in advance for information on the following applications: ? special applications (such as for airplanes, aerospace, automotive equipment, traffic signaling equipment, combustion equipment, life support systems and safety devices) in which exceptional quality and reliability are required, or if the failure or malfunction of the products may directly jeopardize life or harm the human body. it is to be understood that our company shall not be held responsible for any damage incurred as a result of or in connection with your using the products described in this book for any special application, unless our company agrees to your using the products in this book for any special application. (4) the products and product specifications described in this book are subject to change without notice for modification and/or im- provement. at the final stage of your design, purchasing, or use of the products, therefore, ask for the most up-to-date product standards in advance to make sure that the latest specifications satisfy your requirements. (5) when designing your equipment, comply with the range of absolute maximum rating and the guaranteed operating conditions (operating power supply voltage and operating environment etc.). especially, please be careful not to exceed the range of absolute maximum rating on the transient state, such as power-on, power-off and mode-switching. otherwise, we will not be liable for any defect which may arise later in your equipment. even when the products are used within the guaranteed values, take into the consideration of incidence of break down and failure mode, possible to occur to semiconductor products. measures on the systems such as redundant design, arresting the spread of fire or preventing glitch are recommended in order to prevent physical injury, fire, social damages, for example, by using the products. (6) comply with the instructions for use in order to prevent breakdown and characteristics change due to external factors (esd, eos, thermal stress and mechanical stress) at the time of handling, mounting or at customer's process. when using products for which damp-proof packing is required, satisfy the conditions, such as shelf life and the elapsed time since first opening the packages. (7) this book may be not reprinted or reproduced whether wholly or partially, without the prior written permission of our company. 20100202

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