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TB62731FUG toshiba bicd digital integrated circuit silicon monolithic TB62731FUG step-up dc-dc converter for white led driver the TB62731FUG is an led driver that uses a high power efficiency step-up dc-dc converter. the converter turns on/off 2 to 6 white leds in series. the ic incorporates an n-channel mosfet transistor used for coil-switching and a function that reduces the led current in response to increase in temperature. the mean led current can be easily set using an external resistor. the ic is ideal as a driver for led light sources used as liquid crystal backlights for pdas, cellular phones, and handy terminals. features ? maximum output voltage: vo 28 v ? mean led current values set according to external resistor 14 ma (typ.) @r_sens = 2.7 ? 20 ma (typ.) @r_sens = 1.8 ? ? supply power: up to 320 mw supported ? compact package: ssop6-p-0.95b, 6 pins ? built-in temperature derating function: led current derated automatically depending on temperature ? high power efficiency up to 80% of peak power efficiency achieved using recommended components ron = 2.0 ? (typ.) @v in = 3.2~5.5 v built-in low ron power mos switch pin assignment (top view) weight: 0.016 g (typ.) k gnd shdn a gnd v cc company headquarters 3 northway lane n orth la t ham , new york 12110 toll free: 800.984.5337 fax: 518 .785 . 47 25 web: www.marktechopto.com | email: info@marktechopto.com california sales office: 950 south coast drive, suite 265 costa mesa, california 92626 toll free: 800.984.5337 fax: 714.850.9314 company headquarters 3 northway lane n orth la t ham , new york 12110 toll free: 800.984.5337 fax: 518 .785 . 47 25 web: www.marktechopto.com | email: info@marktechopto.com california sales office: 950 south coast drive, suite 265 costa mesa, california 92626 toll free: 800.984.5337 fax: 714.850.9314
TB62731FUG 2004-09-14 2 block diagram pin functions no symbol function 1 k pin connecting led cathode to resistor used to set current. feedback pin for voltage waveforms for controlling the led constant current. 2, 5 gnd ground pin for the logic 3 shdn ic enable pin. low, standby mode takes effect and pin a is turned off. 4 v cc input pin for power supply for operating the ic. operating voltage range: 3.0~5.5 v 6 a dc-dc converter switch pin. the switch is an n-channel mosfet transistor. note: connect both gnd pins to ground. shdn osc s q r buffer 350 khz stb 0.12 v a v cc ref i (add) i (sub) a k gnd gnd 0.5 :
TB62731FUG 2004-09-14 3 absolute maximum ratings (unless otherwise specified, t opr 25c) characteristics symbol rating unit supply voltage v cc 0.3~ 6.0 v input voltage v in 0.3~ v cc 0.3 v pin a (anode) current i o (a) 270 ma pin a voltage v o (a) 0.3~ 28 v 0.41 (ic only) power dissipation p d 0.47 (ic mounted on pcb) (note) w r th (j-a) 1 300 (ic only) saturation thermal resistance r th (j-a) 2 260 (ic mounted on pcb) c/w operating temperature range t opr 40~ 85 c storage temperature range t stg 40~ 150 c maximum junction temperature t j 125 c note: the power dissipation is derated by 3.8 mw/ q c from the maximum rating for every 1c exceeding the ambient temperature of 25 q c (when the ic is mounted on a pcb). recommended operating conditions (unless otherwise specified, t opr 40~85c) characteristics symbol test circuit test condition min typ. max unit supply voltage v cc 3.0 4.3 v shdn pin high-level input voltage v ih v cc 0.5 v cc v shdn pin low-level input voltage v il 0 0.5 v shdn pin high-level input pulse width tpw shdn 500 p s set led current (mean) i o v o (a) v in 3.0 v, v out 16 v 5 20 ma
TB62731FUG 2004-09-14 4 electrical characteristics (unless otherwise specified, ta 40~85c, v cc 3.0~5.5 v) characteristics symbol test circuit test condition min typ. max unit supply voltage v cc 3.0 5.5 v current consumption at operation i cc (on) v cc 3.6 v 0.6 0.9 ma current consumption at standby i cc (shdn) shdn 0 v 0.5 1.0 p a shdn pin current i_shdn shdn v cc , built-in pull-down resistor 4.2 7 p a internal mos transistor on-resistance ron i (a) 270 ma, including detected resistance 2.0 2.5 : internal mos transistor switching frequency f osc 275 350 425 khz pin a voltage v o (a) 28 v pin a current i o (a) 210 240 270 ma pin a leakage current i oz (a) 0.5 1 p a set led current (mean) i o v cc 3.2~4.2 v, r_sens 1.8 : t opr 25c (note 1) 17.6 20 22.4 ma pin k derating start ambient temperature tdel equivalent to r_sens 1.8 : , l 4.7 p h, v o 16 v 45 (note 2) c note 1: due to operation of the temperature derating function, measure when ta 25 q c. note that fluctuation in r_sens resistors is not included in the specified value. i o may be different from the specified value due to the relation between the inductor value and load. note 2: this rating is guaranteed by the design.
TB62731FUG 2004-09-14 5 figure 1 application circuit the basic TB62731FUG circuit uses a step-up dc-dc converter and burst control of the current pulse. basic operation the internal mos transistor (nmos) is turned on at f osc 350 khz, charging energy to the inductor. the inductance current il increases from 0. when il ilpeak 240 ma (typ.) or when 5/6 (83.3%) of f osc ( 350 khz) is reached, the transistor is turned off. at that time, the coil maintains il ilpeak, the schottky diode is turned on, and il ic2 flows. then, ic2 decreases, reaching il 0. the above operation repeats. when ic2 is fully charged, the surplus current becomes i o , which flows to the led. the graph below shows details of the basic pulse used for burst control. figure 2 switching waveform of inductance ilpeak 240 ma (typ.) il, ilpeak maximum duty: 83.3% of f osc with low inductance with hi g h inductance t 1/f osc , f osc 350 khz (typ.) v in osc s q r buffer 350 khz stb 0.12 v a ref i (add) i (sub) a k gnd r_sens 0.5 : v cc c1 nmos il, ilpeak ic2 c2 i o shdn
TB62731FUG 2004-09-14 6 figure 3 burst control waveforms burst control burst control is control of the number of current pulses, shown in the graph on the previous page. control is repeated in desired cycles. the current pulse in the graph is the charged current on capacitor 2 (c2) for output. the current pulse is supplied to the led as current discharged from the output-side capacitor. the current pulse flows to gnd via r_sens. the waveform of the voltage charged on the output-side capacitor is fed back to the ic from pin k via c2. the internal circuit which uses pin k for input controls the number of current pulses so that the mean voltage value of the obtained voltage waveform is 36 mv. as a result, the output current is controlled as the constant current ( mean current). connecting r_sens 1.8 : obtains the mean current (36 mv y 1.8 : 20 ma). current is controlled by pfm (pulse frequency modulation) because the time when the output pulse is generated varies (increases/decreases). a prerequisite is that the input power from v in is larger than the output power to the led load. the constant current is maintained by fixing a pulse stop time of 7.5~15 p s and increasing/decreasing the number of current pulses. the number of current pulses is fewer when the input power exceeds the output power, larger when the input power is less than the output power. the burst frequency (pulse generation frequency) at controlled constant current is calculated as follows: fburst [hz] (number of current pulses x (1/275~1/350 khz) pulse stop time (7.5~15 p s) . . . formula 1 the ic is designed to supply a load power of 320 mw (min). generally, a step-up inductance of 47 p h is used for optimum design for the load power of 320 mw. when the load power is small, the inductance must be small. make sure the following condition for led load between pins a and k is satisfied: v in (v cc ) led vf total note that, regardless of control by the ic, leds are always on. pin a voltage pin a current (external inductance current) pin k voltage (current charged on capacitor) pulse output time width f osc 350 khz maximum duty width for inductor on: 83.3% of f osc pulse stop time width: 7.5 p s (min)~15 p s (max) repetition of waveforms at left i a (peak) 240 ma (typ.)
TB62731FUG 2004-09-14 7 standby operation the shdn pin is used to set normal or standby operation. when shdn is set to low, the operation is standby; when the pin is high, the led is turned on. current consumption in standby mode is 1 p a (max). output-side capacitor setting when the output-side capacitor (c2) 0.1 p f, the peak current to be supplied to leds is expected to be the set current 5~ 8 ma. when c2 0.01 p f, the peak current is expected to be the set current 20~30 ma; when c2 1 p f, it is the set current 2~3 ma. toshiba recommend c2 1 p f or more considering the led max if. the ic is used only for lighting leds. the ic does not finely control output current ripples. this is because eliminating ripples is considered unnecessary as the led emittance is recognized as the integral amount. external inductance setting the minimum external inductance is calculated as follows: l ( p h) ((k u p o ) v in min u i o ) u (1/f osc min) u 2 u (1/ip min u ip min) . . . formula 2 the above parameters are described below: p o : output power (power required by led load) p o (w) vf led u if led vf schottky u if led r_sens u if led u if led led forward current: if led (ma) set current: i o (ma), led forward voltage: vf led (v), schottky diode forward voltage: vf schottky (v), setting resistance: r_sens ( : ) v in min (v): minimum input voltage (battery voltage) if the input voltage includes a resistance component, take the voltage drop into consideration for the minimum input voltage. the input current i in is roughly estimated as follows: i in (ma) vfled u i o u (1/ k ) u (1/v in ) . . . formula 3 when min v in 3.2 (v), vfled 16 (v), i o 18 (ma), and k ! 75 (%), then i in 0.12 (ma). as a result, the voltage drops by 1.2 v due to the 1- : dc resistance component. because the ic?s minimum v cc 3.0 v, the minimum v in is 3.12 v (v in ! 3.12 v). i o (a): mean current value set according to resistance r_sens ( : ) f osc (hz): switching frequency of internal mos transistor specified values for f osc (khz): 275 min, 350 typ., 475 max ip (a): peak current value supplied to external inductor specified values for ip (a): 230 min, 240 typ., 270 max k: margin of output power k 1.1~1.3 the ideal condition is to give 1.05 to 1.3 times the output power p o as the input power. the loss of the ic is assumed to be included in the margin. if k is too large, it may not be possible for the current characteristic to be the specified value. note that k ! 1.
TB62731FUG 2004-09-14 8 substitute the following conditions in formula 2. supply voltage v in 3.0~4.3 (v) output-side capacitor c2 1 ( p f) . . . c2 is ignored in the calculation. where it is assumed that, vfled 16 (v), vf schottky 0.3 (v), r_sens 1.8 ( : ), i o 20 (ma), k 1.1 vfled: led vf vf schottky: schottky diode vf r_sens: setting resistance i o : set current k: margin l ( p h) ((1.1 u 16 u 0.02) 3 u 0.02) u (1/275e3) u 2 u (1/(0.21 u 0.21)) 48.1 ( p h, v in 3.0 v) 43.8 ( p h, v in 4.3 v) thus, 48.1 ( p h) is selected when the input voltage is low, 3.0 v. note that the calculation does not consider fluctuations in inductance. toshiba recommend selection of an inductance of 1.2 times the calculated value. the recommended inductance under the above conditions is l ( p h) 48.1 ( p h) u 1.2 ! 57.7 ( p h).
TB62731FUG 2004-09-14 9 selection of r_sens resistance between pin k and gnd r_sens ( : ) is used for setting output current i o . the mean output current i o can be set according to the resistance. the mean current i o (ma) to be set is roughly calculated as follows: i o (ma) 36 (mv) y r_sens ( : ) for example, when r_sens 1.8 ( : ), i o 20 (ma). take a current error of r 10% (not including r_sens error) into consideration. the ic has a minimum output p o 320 (ma, choke coil 47 p h). at that time, if the product of mean current i o and output voltage v o exceeds p o 320 (mw), mean current i o may become less than the desired value. if the ic is not connected to the output-side capacitor (for smoothing), the set current i o can be obtained. at that time, because the current flowing to the led is a pulse current with a maximum peak value of 270 ma, make sure that surge current ifp (ma) does not flow to the led. toshiba recommend use of components with low reactance (parasitic inductance) and minimized pcb wiring. toshiba also recommend allocating components in the application circuit diagram as near each other as possible. figure 4 resistance for setting current r_sens ( : ) relation between set current io and setting resistance r_sens (typical value: v cc 3.6 v, ta 25 q c) set current i o (ma) 0 10 9.1 8.2 6.8 5.6 4.7 3.3 2.7 2.2 2 1.8 1.5 1.2 1 10 20 30 40 : i o (ma)
TB62731FUG 2004-09-14 10 output derating function toshiba recommend derating the led current depending on the increase in ambient temperature. the TB62731FUG is designed to ensure safe and efficient driving of white leds used as backlight sources for color lcds. the ic incorporates a function that derates current according to the set temperature (the ambient temperature when the ic is mounted), ta. the ic features an output current that varies according to the internally-detected temperature t js as follows: when t js 45 ( q c), output current is 100%; when t js 100 ( q c), output current is 0%. the derating start temperature t s ( q c) is determined based on ta (ta ts when the ic is not operating) by subtracting the self-generated temperature t up ( q c) from t js 45 ( q c). t s ( q c) 45 ( q c) t up ( q c) . . . formula 4 the derating characteristic is as shown in the graph below, figure 5, which shows the relation between output current change ratio and internally-detected temperature (ic temperature) t js . the self-generated temperature t up ( q c) is calculated as follows: t up ( q c) (p loss (w) p parts (w)) u t ja ( q c/w) ) . . . formula 5 p loss: power loss p parts: power loss of parts t ja : package saturation thermal resistance ( : ) the parameters are described below: dc resistance of inductor: rdc ( : ) led forward current: if led (a) led forward voltage: vf led (v) schottky diode forward voltage: vf schottky (v) setting resistance: r_sens p loss (w) a p o (w) y k (%) p o (w) p o : output power k : power efficiency p parts (w) a rdc u i in vf schottky u if led r_sens u if led u if led t ja ( q c/w) d 260 ( q c/w) max when ic mounted on pcb p o (w) v o (v) u i o (a) v o : vf led output voltage i o : mean output current = set current p i (w) v in (v) u i in (a) p i : input power v in : input voltage i in : mean input current k (%) 100 u p o (w) y p i (w) example of calculation: where the measurement result for any lighting circuit shows the following values: rdc 0.5 ( : ), p o 320 (mw), i in 0.1 (ma), i o 20 (ma), r_sens 1.8 ( : ), vf schottky 0.3 (v), and k 70 (%)
TB62731FUG 2004-09-14 11 the self-generated temperature t up ( q c) is calculated as follows: t up (c) ((0.32 (0.32 u 0.7)) (0.5 u 0.1 0.3 u 0.02 1.8 u 0.02 u 0.02)) u 260 10.2 (c) thus, the derating start temperature t s ( q c) is calculated as follows: t s (c) 45 (c) 10.4 (c) 34.8 (c) as a result, i o is controlled in the recommended current range as shown in figure 5. since saturation thermal resistance t ja 260 ( q c/w) is the maximum value, t ja 210~260 ( q c/w) is used as a mounting condition. depending on the ic characteristics, peripherals, and use environment, the derating start temperature fluctuates among ics. figure 5 derating function of set current 0 0 25 50 75 100 20 40 60 80 100 120 change from t s = 34.8 q c (20 ma = 100%) change according to t js recommended led current range (converted by 25 ma) temperatures t s ( q c) and t js ( q c) output current change ratio (%) [%]
TB62731FUG 2004-09-14 12 current consumption at normal operation i cc (on) current consumption at shutdown i cc (shdn) output switching frequency v cc (v) v cc (v) v cc (v) current consumption ( p a) current consumption at shutdown ( p a) output switching frequency (khz) 0 0.5 0.3 0.1 5.5 3 4 4.5 0.2 0.4 3.5 5 300 400 360 320 5.5 3 4 4.5 340 380 3.5 5 TB62731FUG 4 3 2 5 1 6 v cc TB62731FUG 4 3 2 5 1 6 v cc TB62731FUG 4 3 2 5 1 6 v cc f osc 0 900 300 800 100 5.5 3 4 500 4.5 200 600 400 700 3.5 5
TB62731FUG 2004-09-14 13 application circuit example 1 (characteristic using recommended coil as reference) though it is necessary to consider the dc resistance of l1, an inductance of 33 to 47 (typ.) to 68 p h is suitable for turning on four leds. input voltage v in (v) in p ut volta g e ? p ower efficienc y /mean current input voltage v in (v) power efficiency k (%) mean current i f (ma) 40 100 70 50 4.2 3.2 3.6 3.8 60 80 3.4 4 90 10 25 15 20 k i f 40 100 70 50 4.2 3.2 3.6 3.8 60 80 3.4 4 90 10 25 15 20 k i f 40 100 70 50 4.2 3.2 3.6 3.8 60 80 3.4 4 90 10 25 15 20 k i f in p ut volta g e ? p ower efficienc y /mean current input voltage v in (v) power efficiency k (%) mean current i f (ma) input volta g e ? power efficienc y /mean current power efficiency k (%) mean current i f (ma) l1: toko a914byw-470m s-di: toshiba 1ss404 20 v/1a led: nichia nscw215t r_sens: rohm mcr03-1r8 r_ sens 1.8 : v in 3.2 v~4.2 v c1 10 p f on off i f 20 ma l1 47 p h s-di c2 1 p f v cc a shdn gnd gnd k l1: toko a914byw-470m s-di: toshiba 1ss404 20 v/1a led: nichia nscw215t r_sens: rohm mcr03-1r8 r_ sens 1.8 : v in 3.2 v~4.2 v c1 10 p f on off l1 47 p h s-di c2 1 p f v cc a shdn gnd gnd k i f 20 ma l1: toko a914byw-470m s-di: toshiba 1ss404 20 v/1a led: nichia nscw215t r_sens: rohm mcr03-1r8 r_sens 1.8 : v in 3.2 v~4.2 v c1 10 p f on off i f 20 ma l1 47 p h s-di c2 1 p f v cc a shdn gnd gnd k
TB62731FUG 2004-09-14 14 application circuit example 2 (characteristic using flat coil for handy terminal as reference) flat coils suitable for handy terminals have a large dc resistance; thus, the power efficiency drops slightly, to about 70%. input voltage v in (v) in p ut volta g e ? p ower efficienc y /mean current power efficiency k (%) average i f (ma) in p ut volta g e ? p ower efficienc y /mean current input voltage v in (v) power efficiency k (%) average i f (ma) in p ut volta g e ? p ower efficienc y /mean current input voltage v in (v) power efficiency k (%) average i f (ma) 40 100 70 50 4.2 3.2 3.6 3.8 60 80 3.4 4 90 10 25 15 20 k i f 40 100 70 50 4.2 3.2 3.6 3.8 60 80 3.4 4 90 10 25 15 20 k i f 40 100 70 50 4.2 3.2 3.6 3.8 60 80 3.4 4 90 10 25 15 20 k i f l1: toko a914byw-270m s-di: toshiba 1ss404 20 v/1a led: nichia nscw215t r_sens: susumu rl0510s-1r8 r_sens 1.8 : v in 3.2 v~4.2 v c1 10 p f on off i f 20 ma l1 27 p h s-di c2 1 p f v cc a shdn gnd gnd k l1: tdk ldr344812t-390 s-di: toshiba 1ss404 20 v/1a led: nichia nscw215t r_sens: susumu rl0510s-1r8 r_sens 1.8 : v in 3.2 v~4.2 v c1 10 p f on off i f 20 ma l1 39 p h s-di c2 1 p f v cc a shdn gnd gnd k l1: tdk ldr344812t-440 s-di: toshiba 1ss404 20 v/1a led: nichia nscw215t r_sens: rohm mcr03-1r8 r_sens 1.8 : v in 3.2 v~4.2 v c1 10 p f on off i f 20 ma or 16 ma l1 44 p h s-di c2 1 p f v cc a shdn gnd gnd k
TB62731FUG 2004-09-14 15 power efficiency k (%) input voltage v in (v) 40 100 70 50 4.2 3.2 3.6 3.8 60 80 3.4 4 90 0 20 k i f 15 10 5 40 100 70 50 4.2 3.2 3.6 3.8 60 80 3.4 4 90 4 10 6 8 k i f 9 7 5 input volta g e ? power efficienc y /mean current power efficiency k (%) mean current i f (ma) input volta g e ? power efficienc y /mean current input voltage v in (v) mean current i f (ma) l1: toko a914byw-4r7 s-di: toshiba 1ss404 20 v/1a led: nichia nscw215t r_sens: r_sens 5.1 : v in 3.2 v~4.2 v c1 4.7 p f on off i f 8.5 ma l1 4.7 p h s-di c2 1 p f v cc a shdn gnd gnd k l1: sumitomo special metals cxld (cxad) 120-150 s-di: toshiba 1ss404 20 v/1a led: nichia nscw215t r_sens: r_sens 2.4 : v in 3.2 v~4.2 v c1 4.7 p f on off i f 8.5 ma l1 15 p h s-di c2 1 p f v cc a shdn gnd gnd k
TB62731FUG 2004-09-14 16 package dimensions weight: 0.016 g (typ.)
TB62731FUG 2004-09-14 17 x the information contained herein is subject to change without notice. x the information contained herein is presented only as a guide for the applications of our products. no responsibility is assumed by toshiba for any infringements of patents or other rights of the third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of toshiba or others. x toshiba is continually working to improve the quality an d reliability of its products. nevertheless, semiconductor devices in general can malfunction or fail due to their inherent electrical sensitivity and vulnerability to physical stress. it is the responsibility of the buyer, when utilizing toshiba products, to comply with the standards of safety in making a safe design for the entire system, and to avoid situations in which a malfunction or failure of such toshiba products could cause loss of human life, bodily injury or damage to property. in developing your designs, please ensure that toshiba products are used within specified operating ranges as set forth in the most recent toshiba products specifications. also, please keep in mind the precautions and conditions set forth in the ?handling guide for semiconductor devices,? or ?toshiba semiconductor reliability handbook? etc.. x the toshiba products listed in this document are intended for usage in general electronics applications (computer, personal equipment, office equipment, measuring equipment, industrial robotics, domestic appliances, etc.). these toshiba products are neither intended nor warranted for usage in equipment that requires extraordinarily high quality and/or reliability or a malfuncti on or failure of which may cause loss of human life or bodily injury (?unintended usage?). unintended usage include atomic energy control instruments, airplane or spaceship instruments, transportation instruments, traffic signal instruments, combustion control instruments, medical instruments, all types of safety devices, etc.. unintended usage of toshiba products listed in this document shall be made at the customer?s own risk. x the products described in this document are subject to the foreign exchange and foreign trade laws. x toshiba products should not be embedded to the downstream products which are prohibited to be produced and sold, under any law and regulations. 030619eba restrictions on product use about solderabilit y, following conditions were confirmed x solderability (1) use of sn-63pb solder bath solder bath temperature 230c dipping time 5 seconds the number of times once use of r-type flux (2) use of sn-3.0ag-0.5cu solder bath solder bath temperature 245c dipping time 5 seconds the number of times once use of r-type flux

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