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1 rt9284a/b ds9284a/b-07 april 2011 www.richtek.com pin configurations applications z camera flash white led z mobile phone, smart phone led backlight z pda led backlight z digital still camera z camcorder tiny package, high performance, constant current switching regulator for white led ordering information top view features z z z z z v in operating range : 2.7v to 5.5v z z z z z maximum output voltage up to 20v z z z z z dimming with zero-inrush and wide frequency range of 100 to 100khz z z z z z over voltage protection z z z z z output current up to 100ma at v out : 12v z z z z z zero shutdown supply current z z z z z minimize the external component z z z z z small lc filter z z z z z internal soft start z z z z z rohs compliant and 100% lead (pb)-free general description the rt9284a/b is a compact, high efficient and high integration led driver. internal 22v mosfet can support 2 to 5 white leds for backlighting and camera flashing. highly integration and internal compensation network minimizes as 5 external component counts. optimized operation frequency can meet the requirement of small lc filters value and low operation current with high efficiency. internal soft start function can reduce the inrush current. tiny package type of tsot-23-5 and tsot-23-6 packages provide the best solution for pcb space saving and total bom cost. marking information for marking information, contact our sales representative directly or through a richtek distributor located in your area. note : richtek products are : ` rohs compliant and compatible with the current require- ments of ipc/jedec j-std-020. ` suitable for use in snpb or pb-free soldering processes. tsot-23-6 tsot-23-5 lx gnd fb vdd en 4 23 5 lx gnd fb vdd ovp en 4 23 5 6 rt9284 package type j5 : tsot-23-5 j6 : tsot-23-6 lead plating system p : pb free g : green (halogen free and pb free) ovp voltage 15 : 15v 20 : 20v ( ) fb voltage a : 1.235v b : 0.25v -
2 rt9284a/b www.richtek.com ds9284a/b-07 april 2011 typical application circuit figure 1. application for driving 3 series wleds figure 2. application for driving 4 series wleds figure 4. application for constant output voltage vdd gnd lx fb ovp rt9284 v in en 6 4 2 3 5 1 i led + dimming control 2.7v to 5.5v c1 1uf c2 1uf/16v r1 d1 ss0520 l1 4.7uh to 22uh 100hz-100khz ovp 15v figure 3. application for driving 5 series wleds vdd gnd lx fb ovp rt9284a v in en 6 4 2 3 5 1 + 2.7v to 5.5v c1 1uf c2 r2 d1 ss0520 l1 4.7uh to 22uh r1 130k 15k v out 12v ovp 15v 1uf/16v v fb = 1.235v vdd gnd lx fb ovp rt9284 v in en 6 4 2 3 5 1 i led + dimming control 2.7v to 5.5v c1 1uf c2 r1 d1 ss0520 l1 4.7uh to 22uh 100hz-100khz 1uf/25v ovp 18v ovp 15v r2 600k vdd gnd lx fb ovp rt9284b v in en 6 4 2 3 5 1 i led + dimming control 2.7v to 5.5v c1 1uf c2 1uf/25v r1 d1 ss0520 l1 4.7uh to 22uh 100hz-100khz ovp 20v v fb = 0.25v
3 rt9284a/b ds9284a/b-07 april 2011 www.richtek.com pin description pin no. tsot-23-5 tsot-23-6 pin name pin function 1 1 lx switch pin. connect this pin to inductor and catch diode. minimize the track area to reduce emi. 2 2 gnd ground pin 3 3 fb feedback reference voltage pin. series connect a resistor between wled and ground as a current sense. sense the current feedback voltage to set the current rating. 4 4 en chip enable (active high). voltage sensing input to trigger the function of over voltage protection. note that this pin is high impedance. there should be a pull low 100k resistor connected to gnd when the control signal is floating. -- 5 ovp over voltage protection pin. voltage sensing input to trigger the function of over voltage protection. leave it unconnected to disable this function. 5 6 vdd supply input voltage pin. bypass 1uf capacitor to gnd to reduce the input noise. function block diagram current bias soft start ocp 750ma bandgap ovp uvlo timer 5ms en ovp vdd + - + - v ref pwm logic 1.2mhz osc gnd fb lx v ref ibias protection circuit buffer
4 rt9284a/b www.richtek.com ds9284a/b-07 april 2011 absolute maximum ratings (note 1) z supply input voltage ---------------------------------------------------------------------------------------------------- ? 0.3v to 7v z lx input voltage ---------------------------------------------------------------------------------------------------------- ? 0.3v to 22v z ovp v oltage -------------------------------------------------------------------------------------------------------------- ? 0.3v to 22v z the other pins ----------------------------------------------------------------------------------------------------------- ? 0.3v to 6v z power dissipation, p d @ t a = 25 c tsot-23-5 ----------------------------------------------------------------------------------------------------------------- 0.455w tsot-23-6 ----------------------------------------------------------------------------------------------------------------- 0.455w z package thermal resistance (note 2) tsot-23-5, ja ------------------------------------------------------------------------------------------------------------ 220 c/w tsot-23-6, ja ------------------------------------------------------------------------------------------------------------ 220 c/w z lead temperature (soldering, 10 sec.) ----------------------------------------------------------------------------- 260 c z junction temperature --------------------------------------------------------------------------------------------------- 150 c z storage temperature range ------------------------------------------------------------------------------------------- ? 65 c to 150 c z esd susceptibility (note 3) hbm (human body mode) --------------------------------------------------------------------------------------------- 2kv mm (machine mode) ---------------------------------------------------------------------------------------------------- 200v recommended operating conditions (note 4) z supply input v oltage ---------------------------------------------------------------------------------------------------- 2.7v to 5.5v z junction temperature range ------------------------------------------------------------------------------------------ ? 40 c to 125 c z ambient temperature range ------------------------------------------------------------------------------------------ ? 40 c to 85 c electrical characteristics to be continued (v in = 3.7v, t a = 25 c unless otherwise specified) parameter symbol test conditions min typ max unit system supply input operation voltage range v dd 2.7 -- 5.5 v under voltage lock out v dd 1.8 2.2 2.5 v quiescent current i dd fb = 1.5v, no switch 50 300 1000 ua supply current i dd fb = 0v, switch 0.1 2 3 ma shut down current i dd v en < 0.4v -- -- 1 ua line regulation v in : 3.0~4.3v -- 3 -- % oscillator operation frequency f osc 0.9 1.2 1.5 mhz maximum duty cycle 85 -- -- % dimming frequency 100 -- 100k hz reference voltage rt9284a 1.173 1.235 1.296 feedback voltage (note 5) rt9284b 0.237 0.25 0.263 v
5 rt9284a/b ds9284a/b-07 april 2011 www.richtek.com note 1. stresses listed as the above ? absolute maximum ratings ? may cause permanent damage to the device. these are for stress ratings. functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. note 2. ja is measured in the natural convection at t a = 25 c on a low effective thermal conductivity test board of jedec 51-3 thermal measurement standard. note 3. devices are esd sensitive. handling precaution recommended. note 4. the device is not guaranteed to function outside its operating conditions. note 5. floating the ovp pin to disable ovp function. parameter symbol test condition min typ max unit mosfet on resistance of mosfet r ds(on) -- 0.75 -- protection for 2,3,4 wleds application 14 15 16 ovp threshold v ovp for 5 wled application 19 20 21 v ovp sink current -- 5 -- a ocp -- 750 -- ma shut down voltage v en -- -- 0.4 v enable voltage v en 1.5 -- -- v
6 rt9284a/b www.richtek.com ds9284a/b-07 april 2011 typical operating characteristics led current vs. input voltage 18 18.5 19 19.5 20 20.5 21 21.5 22 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 input voltage (v) led current (ma) 4wleds, l = 10 h maximum duty cycle vs. v dd 85% 86% 87% 88% 89% 90% 91% 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 v dd (v) maximum duty cycle (%) 91 90 89 88 87 86 85 por (rising/falling) vs. temperature 1.5 1.7 1.9 2.1 2.3 2.5 2.7 -40-30-20-10 0 102030405060708090 temperature por (v) ( c) rising falling shut down voltage vs. input voltage 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 input voltage (v) shut down voltage (v) -45 c 25 c 85 c enable voltage v s. input voltage 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 input voltage (v) enable voltage (v) -45 c 25 c 85 c efficiency vs. input voltage 80.5 81 81.5 82 82.5 83 83.5 84 3 3.2 3.4 3.6 3.8 4 4.2 4.4 input voltage (v) efficiency (%) 3wleds 4wleds i led = 20ma, l = 4.7 h, dcr = 0.15
7 rt9284a/b ds9284a/b-07 april 2011 www.richtek.com dimming operation time (400 s/div) i in i led en (5v/div) (10ma/div) f = 1khz, duty = 50% 4wleds, v in = 3.7v, i led = 20ma, l = 10 h (100ma/div) switching frequency vs. temperature 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 -40-30-20-10 0 102030405060708090 temperature switching frequency (mhz) ( c) switching current vs. input voltage 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 input voltage (v) switching current (ma) -45 c 25 c 85 c dimming operation time (2ms/div) i in i led en (5v/div) (10ma/div) f = 100hz, duty = 50% 4wleds, v in = 3.7v, i led = 20ma, l = 10 h (50ma/div) dimming operation time (40 s/div) i in i led en (5v/div) (10ma/div) f = 10khz, duty = 50% 4wleds, v in = 3.7v, i led = 20ma, l = 10 h (100ma/div) feedback voltage vs. temperature 250.6 250.8 251 251.2 251.4 251.6 251.8 252 252.2 -40-30-20-10 0 102030405060708090 temperature feedback voltage (mv) ( c)
8 rt9284a/b www.richtek.com ds9284a/b-07 april 2011 normal operation time (400ns/div) v in lx i in v out (5v/div) (2v/div) (10v/div) (100ma/div) 4wleds, v in = 3.0v i led = 20ma, l = 10 h normal operation time (400ns/div) v in lx i in v out (5v/div) (2v/div) (10v/div) (100ma/div) 4wleds, v in = 3.7v i led = 20ma, l = 10 h dimming operation time (4 s/div) i in i led en (5v/div) (10ma/div) f = 100khz, duty = 50% 4wleds, v in = 3.7v, i led = 20ma, l = 10 h (100ma/div) inrush current time (500 s/div) i in v in en (2v/div) (100ma/div) 4wleds, v in = 3.0v, i led = 20ma, l = 4.7 h (5v/div) v out (2v/div) inrush current time (500 s/div) i in v in en (2v/div) (100ma/div) 4wleds, v in = 4.3v, i led = 20ma, l = 4.7 h (5v/div) v out (2v/div) ocp time (25 s/div) i lx lx (500ma/div) l = 10 h (20v/div) v out (10v/div)
9 rt9284a/b ds9284a/b-07 april 2011 www.richtek.com normal operation time (400ns/div) v in lx i in v out (5v/div) (2v/div) (10v/div) (100ma/div) 4wleds, v in = 5.5v i led = 20ma, l = 10 h normal operation time (400ns/div) v in lx i in v out (5v/div) (2v/div) (10v/div) (100ma/div) 4wleds, v in = 4.3v i led = 20ma, l = 10 h
10 rt9284a/b www.richtek.com ds9284a/b-07 april 2011 application information power sequence the rt9284a/b must take notice of the power sequence. the power sequence of rt9284a/b has to vdd early than en or else the rt9284a/b maybe fall into the unknown state to result in rt9284a/b turn off. dimming control a. using a pwm signal to en pin for controlling the led brightness, the rt9284a/b can perform the dimming control by applying a pwm signal to en pin. the internal soft start and the wide range dimming frequency from100 to100khz can eliminate inrush current and audio noise when dimming. the average led current is proportional to the pwm signal duty cycle. the magnitude of the pwm signal should be higher than the maximum enable voltage of en pin, in order to let the dimming control perform correctly. version feedback reference voltage v fb (v) led current setting i led (a) rt9284a 1.235 i led = 1.235/r1 rt9284b 0.25 i led = 0.25/r1 table 1 figure 6. dimming control using a dc voltage for rt9284a led current control the rt9284a/b regulates the led current by setting the current sense resistor (r1) connecting to feedback and ground. as shown in table 1, the rt9284a feedback voltage (v fb ) is 1.235v and the rt9284b feedback voltage (v fb ) is 0.25v. the led current (i led ) can be set by a resistor r1. in order to have an accurate led current, a precision resistor is preferred (1% is recommended). en < 0.4v en > 1.5v v dd > 2.7v v dd en v out figure 5 b. using a dc voltage using a variable dc voltage to adjust the brightness is a popular method in some applications. the dimming control using a dc voltage circuit is shown in figure 6. according to the superposition theorem, as the dc voltage increases, the voltage contributed to v fb increases and the voltage drop on r2 decreases, i.e. the led current decreases. for example, if the v dc range is from 0v to 2.8v, the selection of resistors in figure 6 sets dimming control of led current from 20ma to 0ma. vdd gnd lx fb ovp rt9284a v in en 6 4 2 3 5 1 i led 2.7v to 5.5v c1 c2 r1 d1 ss0520 l1 4.7uh to 22uh r2 v dc dimming 0v to 2.8v r3 110 10k 13k v en > 1.5v v en < 0.4v c. using a filtered pwm signal: another common application is using a filtered pwm signal as an adjustable dc voltage for led dimming control. a filtered pwm signal acts as the dc voltage to regulate the output current. the recommended application circuit is shown in the figure 7. in this circuit, the output ripple depends on the frequency of pwm signal. for smaller output voltage ripple (<100mv), the recommended frequency of 2.8v pwm signal should be above 2khz. to fix the frequency of pwm signal and change the duty cycle of pwm signal can get different output current. figure 8. shows the relationship between led current and pwm duty cycle. the led current can be calculated by the following equation. dc fb fb led r2 (v v ) v r3 i = r1 ? ?
11 rt9284a/b ds9284a/b-07 april 2011 www.richtek.com figure 7. filtered pwm signal for led dimming control of rt9284a 0 2 4 6 8 10 12 14 16 18 20 0 102030405060708090100 pwm duty (%) led current (ma) figure 8 inductor selection the recommended value of inductor for 3 to 5 wleds applications are 4.7 to 22 h. small size and better efficiency are the major concerns for portable device, such as rt9284a/b used for mobile phone. the inductor should have low core loss at 1.2mhz and low dcr for better efficiency. to avoid inductor saturation current rating should be considered. ) i (i (rms) i peak out d capacitor selection input and output ceramic capacitors of 1 f are recommended for rt9284a/b applications. for better voltage filtering, ceramic capacitors with low esr are recommended. x5r and x7r types are suitable because of their wider voltage and temperature ranges. diode selection schottky diode is a good choice for rt9284a/b because of its low forward voltage drop and fast reverse recovery. using schottky diode can get better efficiency. the high- speed rectification is also a good characteristic of schottky diode for high switching frequency. current rating of the diode must meet the root mean square of the peak current and output average current multiplication as following : the diode ? s reverse breakdown voltage should be larger than the output voltage. ss0520 is recommended schottky diode for rectifier. layout guide z a full gnd plane without gap break. z vcc to gnd noise bypass ? short and wide connection for the 1 f mlcc capacitor between pin6 and pin2. z minimized lx node copper area to reduce emi. z minimized fb node copper area and keep far away from noise sources. figure 9. top layer the led current can be calculated by the following equation. pwm fb fb dc led r2 (v duty v ) v r3 + r i = r1 ? ? vdd gnd lx fb ovp rt9284a v in en 6 4 2 3 5 1 i led 2.7v to 5.5v c1 c2 r1 d1 ss0520 l1 4.7uh to 22uh r2 pwm signal r3 110 10k 10k 2.8v 0v r dc 3k c dc 1uf v en > 1.5v v en < 0.4v
12 rt9284a/b www.richtek.com ds9284a/b-07 april 2011 figure 10. bottom layer
13 rt9284a/b ds9284a/b-07 april 2011 www.richtek.com outline dimension tsot-23-5 surface mount package a a1 e b b d c h l dimensions in millimeters dimensions in inches symbol min max min max a 0.700 1.000 0.028 0.039 a1 0.000 0.100 0.000 0.004 b 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 c 2.591 3.000 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024
rt9284a/b 14 www.richtek.com ds9284a/b-07 april 2011 information that is provided by richtek technology corporation is believed to be accurate and reliable. richtek reserves the ri ght to make any change in circuit design, specification or other related things if necessary without notice at any time. no third party intellectual property inf ringement of the applications should be guaranteed by users when integrating richtek products into any application. no legal re sponsibility for any said applications i s assumed by richtek. richtek technology corporation headquarter 5f, no. 20, taiyuen street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 fax: (8863)5526611 richtek technology corporation taipei office (marketing) 5f, no. 95, minchiuan road, hsintien city taipei county, taiwan, r.o.c. tel: (8862)86672399 fax: (8862)86672377 email: marketing@richtek.com tsot-23-6 surface mount package a a1 e b b d c h l dimensions in millimeters dimensions in inches symbol min max min max a 0.700 1.000 0.028 0.039 a1 0.000 0.100 0.000 0.004 b 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 c 2.591 3.000 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024

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