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RT8510 1 ds8510-00 july 2010 www.richtek.com pin configurations (top view) wqfn-16l 3x3 43v 4-ch led driver general description the RT8510 is a high efficiency driver for white leds. it is designed for lcd panels that employ an array of leds as the lighting source. an integrated switch current mode boost controller drives four strings in parallel and supports up to 12 pieces of led per string. the internal current sinks support a maximum of 2% current mismatching for excellent brightness uniformity in each string of led. to provide enough headroom for current sink operation the boost controller monitors the minimum voltage of feedback pins and regulates an optimized output voltage for power efficiency. the RT8510 has a wide input voltage range from 4.2v to 24v and provide an adjustable 10ma to 40ma led current. the internal 200m , 43v power switch with current-mode control provides cycle-by-cycle over current protection. RT8510 also integrates pwm dimming function for accurate led current control. the input pwm dimming frequency can operate from 120hz to 30khz without inducing any inrush current through the led or inductor. the switching frequency of the RT8510 is adjustable from 500khz to 2mhz, allowing the user flexibility between efficiency and component size. the RT8510 is available in a wqfn-16l 3x3 package. features z z z z z wide input voltage : 4.2v to 24v z z z z z high output voltage : up to 43v z z z z z adjustable channel current : 10ma to 40ma z z z z z channel current accuracy : 3% z z z z z channel current matching : 2% z z z z z pwm dimming frequency : 120hz to 30khz z z z z z adjustable switching frequency : 500khz to 2mhz z z z z z built-in soft-start z z z z z disconnects led in shutdown z z z z z open current sink detection z z z z z adjustable over voltage protection z z z z z over temperature protection z z z z z current limit protection z z z z z thin 16-lead wqfn package z z z z z rohs compliant and halogen free applications z umpc and notebook computer backlight z gps, portable dvd backlight ordering information note : richtek green 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. package type qw : wqfn-16l 3x3 (w-type) operating temperature range g : green (halogen free with commer- cial standard) RT8510 rt iset agnd comp ovp pgnd lx pgnd pwm vin en lx ch4 ch3 ch1 ch2 12 11 10 9 13 14 15 16 1 2 3 4 8 7 6 5 gnd 17
RT8510 2 ds8510-00 july 2010 www.richtek.com function pin description pin no. pin name pin function 1 agnd analog ground of led driver. 2 comp compensation pin for error amplifier. connect a compensation network to ground. 3 iset led current set pin. led current is set by the value of the resistor r iset connected from the iset pin to ground. do not short the iset pin. v iset is typically 0.6v. led iset 95 i = r 4 rt frequency adjust pin. this pin allows setting the switching frequency with a resistor to 500khz to 2mhz. 5 pwm dimming control input. 6 en chip enable (active high). note that this pin is high impedance. there should be a pull low 100k resistor connected to gnd when the control signal is floating. 7 vin power supply input. 8, 9 lx switching pin of boost converter. 10, 11 pgnd power ground of boost converter. 12 ovp sense input for over voltage protection. the detecting threshold is 1.2v. marking information hu= : product code ymdnn : date code typical application circuit hu=ym dnn to be continued RT8510 l ch1 ch2 vin pgnd ovp lx v out 43v max : : : : : : : : : : : : : : : : 10 led string ch3 ch4 v in 4.2v to 24v en d1 c out r ovp2 r ovp1 c in chip enable agnd 12 10, 11 13 14 15 16 1 8, 9 7 6 10f 2m 62k 10h 10f r2 10 c2 1f rt comp r3 iset c3 r rt r iset 2 3 4 10k 10nf c4 1nf 51k 4.75k pwm 5 pwm dimming 100k
RT8510 3 ds8510-00 july 2010 www.richtek.com function block diagram pin no. pin name pin function 13, 14, 15, 16 ch1 to ch 4 current sink for led. leave the pin unconnected, if not used. 17 (exposed pad) gnd the exposed pad must be soldered to a large pcb and connected to gnd for maximum power dissipation. r q s q osc pwm controller + - ocp otp + - 1.2 + - led detection lx ovp iset comp en pgnd 0.4v + - + - + - + - 0.6v : : pwm 4 regulator vin rt agnd ch1 ch2 ch3 ch4 ea
RT8510 4 ds8510-00 july 2010 www.richtek.com absolute maximum ratings (note 1) z supply input v oltage to gnd ------------------------------------------------------------------------------------------- ? 0.3v to 26.5v z en, pwm, iset, comp, rt to gnd --------------------------------------------------------------------------------- ? 0.3v to 26.5v z lx, ovp, ch1, ch2, ch3, ch4 to gnd ----------------------------------------------------------------------------- ? 0.3v to 48v z power dissipation, p d @ t a = 25 c wqfn-16l 3x3 ------------------------------------------------------------------------------------------------------------ 1.471w z package thermal resistance (note 2) wqfn-16l 3x3, ja ------------------------------------------------------------------------------------------------------- 68 c/w wqfn-16l 3x3, jc ------------------------------------------------------------------------------------------------------ 7.5 c/w z lead temperature (soldering, 10 se c.) ------------------------------------------------------------------------------- 260 c z junction temperature ----------------------------------------------------------------------------------------------------- 150 c z storage temperature range -------------------------------------------------------------------------------------------- ? 65 c to 150 c z esd susceptibility (note 3) hbm -------------------------------------------------------------------------------------------------------------------------- 2k v mm ---------------------------------------------------------------------------------------------------------------------------- 2 00v recommended operating conditions (note 4) z supply input voltage, v in ------------------------------------------------------------------------------------------------ 4.2v to 24v z junction temperature range -------------------------------------------------------------------------------------------- ? 40 c to 125 c z ambient temperature range -------------------------------------------------------------------------------------------- ? 40 c to 85 c electrical characteristics parameter symbol test conditions min typ max unit v comp = 0v, no switching -- 1 1.5 vin quiescent current i q v comp = 2v, switching 2 3 ma vin shutdown current i shdn v in = 4.5v, en = 0v -- -- 10 a control input logic high v ih 2 -- -- v en, pwm threshold voltage logic low v il v in = 4.2v to 24v -- -- 0.8 v pwm dimming frequency f pw m 120 -- 30k hz boost converter r rt = 25k -- 2 -- r rt = 51k -- 1 -- switching frequency f osc r rt = 102k -- 0.5 -- mhz lx on resistance (n-mosfet) r ds(on)_n v in > 4.5v -- 0.2 -- minimum on time t mon -- 120 -- ns maximum duty d max v comp = 2v, switching -- 92 -- % lx current limit i lim -- 2 -- a led current programming led current matching i ledm 2v > chx > 0.4v calculating (i (max) ? i (avg) ) / i (avg) x 100%, r iset = 4.75k -- -- 2 % iset pin voltage v iset -- 0.6 -- v led current i chx 2v > chx > 0.4v, r iset = 4.75k 19.4 20 20.6 ma (v in = 4.5v, t a = 25 c unless otherwise specified) to be continued
RT8510 5 ds8510-00 july 2010 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 natural convection at t a = 25 c on a high-effective thermal conductivity four-layer test board of jedec 51-7 thermal measurement standard. the measurement case position of jc is on the exposed pad of the package note 3. devices are esd sensitive. handling precaution is recommended. note 4. the device is not guaranteed to function outside its operating conditions. note 5. guaranteed by design; not subject to production testing. parameter symbol test conditions min typ max unit fault protection ovp threshold v ovp -- 1.2 -- v ovp fail threshold v ovpf -- 50 -- mv thermal shutdown temperature t sd -- 160 -- c led pin under voltage threshold v lsd no connection -- 50 -- mv regulated v chx v chx highest led string voltage, r iset = 4.75k -- 0.4 -- v
RT8510 6 ds8510-00 july 2010 www.richtek.com typical operating characteristics led current vs. temperature 14 16 18 20 22 24 26 -50 -25 0 25 50 75 100 125 temperature (c) led current (ma) v in = 12v, f osc = 1mhz led current vs. input voltage 14 16 18 20 22 24 26 4 9 14 19 24 input voltage (v) led current (ma) f osc = 1mhz ch1 ch2 ch3 ch4 led current vs. pwm duty cycle 0 10 20 30 40 50 60 70 80 90 0 102030405060708090100 duty cycle (%) led current (ma) 10 x 4 leds, f osc = 1mhz pwm = 30khz pwm = 10khz pwm = 1khz pwm = 120hz efficiency vs. input voltage 0 10 20 30 40 50 60 70 80 90 100 4 8 12 16 20 24 input voltage (v) efficiency (%) 10 x 4 leds, f osc = 1mhz v iset vs. temperature 0.40 0.45 0.50 0.55 0.60 0.65 0.70 -50 -25 0 25 50 75 100 125 temperature (c) v iset (v) v in = 12v, f osc = 1mhz v iset vs. input voltage 0.3 0.4 0.5 0.6 0.7 0.8 4 8 12 16 20 24 input voltage (v) v iset (v) f osc = 1mhz
RT8510 7 ds8510-00 july 2010 www.richtek.com switch off current vs. temperature 0.5 0.7 0.9 1.1 1.3 1.5 -50-25 0 25 50 75100125 temperature (c) switch off current (ma) f osc = 1mhz, v in = 4.5v line transient response time (50ms/div) v in (2v/div) i out (50ma/div) v in = 4.5v to 5.5v, f osc = 1mhz line transient response time (50ms/div) v in = 11v to 14v, f osc = 1mhz v in (5v/div) i out (50ma/div) ovp threshold vs. input voltage 1.0 1.1 1.2 1.3 1.4 1.5 4 8 12 16 20 24 input voltage (v) ovp threshold (v) f osc = 1mhz
RT8510 8 ds8510-00 july 2010 www.richtek.com application information the RT8510 is a general purpose 4-ch led driver capable of delivering an adjustable 10 to 40ma led current. the ic is a current mode boost converter integrated with a 43v/2a power switch and can cover a wide v in range from 4.2v to 24v. the switching frequency is adjustable by an external resistor from 500khz to 2mhz. the part integrates built-in soft start, with pwm dimming control; moreover, it provides over voltage, over temperature and current limiting protection features. soft-start the RT8510 equips a built-in soft-start feature to prevent high inrush current during start-up. the soft-start function prevents excessive input current and input voltage droop during power on state. compensation the control loop can be compensates by adjusting the external components connected to the comp pin. the comp pin is the output of the internal error amplifier. the compensation capacitors, c3 and c4, will adjust the integrator zero and pole respectively to maintain stability. moreover, the resistor, r3, will adjust the frequency integrator gain for fast transient response. led connection the RT8510 equips 4-ch led divers with each channel supporting up to 12 leds. if the boost converter input voltage too close to the output voltage, v out ripple will be increased. to prevent this phenomenon, please keep v out higher than 1.2 x v in . the led strings are connected from the output of the boost converter to pins 13, 14, 15 and 16 respectively. if one of the led channel is not used, the led pin should be opened directly. setting and regulation of led current the led current can be calculated by the following equation : where r iset is the resistor between the iset pin and gnd. this setting is the reference for the led current at channel 1-4 and represents the sensed led current for each string. r ovp1 and r ovp2 are the resistors in the voltage divider connected to the ovp pin. if at least one string is in normal operation, the controller will automatically ignore the open strings and continue to regulate the current for the strings in normal operation. it is suggested to use 2m for r ovp2 to reduce loading effect. current limit protection the RT8510 can limit the peak current to achieve over current protection. the RT8510 senses the inductor current during the ? on ? period that flows through the lx pin. the duty cycle depends on the current signal and internal slope compensation in comparison with the error signal. the internal switch will be turned off when the current signal is larger than the internal slope compensation. in the ? off ? period, the inductor current will be decreased until the internal switch is turned on by the oscillator. brightness control the RT8510 brightness dimming control is determined by the signal on the pwm pin with a suggested pwm frequency range from 120hz to 30khz. referring to the following curve, the minimum dimming duty can be as low as 1% for the frequency range from 120hz to 1khz. for the dimming frequency from 1khz to 10khz, the dimming duty is at most 5%. if the frequency is increased to 30khz, the dimming duty will be up to 10%. led iset 95 i r ? ovp2 out(ovp) ovp ovp1 r vv1 r ?? =+ ?? ?? the dc/dc converter regulates the led current according to r iset . over voltage protection the RT8510 integrates over voltage protection (ovp) function. when the voltage at the ovp pin reaches the threshold voltage, the internal switch will be turned off. the internal switch will be turned on again once the voltage at ovp pin drops below its threshold voltage. the ovp threshold voltage is adjustable and can be clamped at a certain voltage level and it can be calculated by the following equation :
RT8510 9 ds8510-00 july 2010 www.richtek.com over temperature protection the RT8510 has over temperature protection function to prevent the ic from overheating due to excessive power dissipation. the otp function will shutdown the ic when junction temperature exceeds 160 c . inductor selection the value of the inductance l can be approximated by the following equation, where the transition is from discontinuous conduction mode (dcm) to continuous conduction mode (ccm) : the duty cycle can be calculated according to the following equation : where v out is the maximum output voltage, v in is the minimum input voltage, f osc is the operating frequency and i out is the total current from all led strings. the boost converter operates in dcm over the entire input voltage range when the inductor value is below this value l. when inductance greater is than l, the converter operates in ccm at the minimum input voltage and may be discontinuous at higher voltages. the inductor must be selected with a saturated current rating that is greater than the peak current provided by the following equation : where is the efficiency of the power converter and t is the operating period. diode selection schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. the power dissipation, reverse voltage rating and pulsating peak current are the important parameters for schottky diode selection. make sure that the diode's peak current rating exceeds i peak and reverse voltage rating exceeds the maximum output voltage. capacitor selection the input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. for most applications, a 10 f ceramic capacitor is sufficient. a value higher or lower may be used depending on the noise level from the input supply and the input current to the converter. it is recommended to choose a ceramic capacitor based on the output voltage ripple requirements. the minimum value of the output capacitor c out is given by the following equation : 2 out osc out d(1d) v l 2f i ? = out in out vv d v ? = out out in peak in vi vdt i v2l =+ figure 1 out out out id c vf = ? where v out is the peak to peak ripple voltage at the output. thermal considerations for continuous operation, do not exceed absolute maximum junction temperature. the maximum power dissipation depends on the thermal resistance of the ic package, pcb layout, rate of surrounding airflow, and difference between junction and ambient temperature. the maximum power dissipation can be calculated by the following formula : p d(max) = (t j(max) ? t a ) / ja where t j(max) is the maximum junction temperature, t a is the ambient temperature, and ja is the junction to ambient thermal resistance. led current vs. pwm duty cycle 0 10 20 30 40 50 60 70 80 90 0 102030405060708090100 duty cycle (%) led current (ma) 40 leds, f osc = 1mhz pwm = 30khz pwm = 10khz pwm = 1khz pwm = 120hz
RT8510 10 ds8510-00 july 2010 www.richtek.com figure 2. derating curve for RT8510 package layout guideline pcb layout is very important for designing switching power converter circuits. the following layout guides should be strictly followed for best performance of the RT8510. ` the power components, l1, d1, c in , c out must be placed as close as possible to reduce current loop. the pcb trace between power components must be as short and wide as possible. ` place l1 and d1as close as possible to lx pin . the trace should be as short and wide as possible. ` the compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. place the compensation components as close as possible to comp pin. ` the exposed pad of the chip should be connected to ground plane for thermal consideration. rt iset agnd comp ovp pgnd lx pgnd pwm vin en lx ch4 ch3 ch1 ch2 12 11 10 9 13 14 15 16 1 2 3 4 8 7 6 5 17 gnd gnd c3 r3 c4 gnd d1 l1 r2 c2 c in + v in c out v out gnd the compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. place the power components as close as possible. the traces should be wide and short especially for the high- current loop. figure 3. pcb layout guide for recommended operating condition specifications of RT8510, the maximum junction temperature is 125 c and t a is the ambient temperature. the junction to ambient thermal resistance, ja , is layout dependent. for wqfn- 16l 3x3 packages, the thermal resistance, ja , is 68 c/ w on a standard jedec 51-7 four-layer thermal test board. the maximum power dissipation at t a = 25 c can be calculated by the following formula : p d(max) = (125 c ? 25 c) / (68 c/w) = 1.471w for wqfn-16l 3x3 package the maximum power dissipation depends on the operating ambient temperature for fixed t j(max) and thermal resistance, ja . for RT8510 package, the derating curve in figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 0 25 50 75 100 125 ambient temperature (c) maximum power dissipation (w ) four-layer pcb
RT8510 11 ds8510-00 july 2010 www.richtek.com 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) 8f, no. 137, lane 235, paochiao road, hsintien city taipei county, taiwan, r.o.c. tel: (8862)89191466 fax: (8862)89191465 email: marketing@richtek.com 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 infringemen t of the applications should be guaranteed by users when integrating richtek products into any application. no legal responsibility for any said applications is assumed b y richtek. outline dimension a a1 a3 d e 1 d2 e2 l b e see detail a dimensions in millimeters dimensions in inches symbol min max min max a 0.700 0.800 0.028 0.031 a1 0.000 0.050 0.000 0.002 a3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 d 2.950 3.050 0.116 0.120 d2 1.300 1.750 0.051 0.069 e 2.950 3.050 0.116 0.120 e2 1.300 1.750 0.051 0.069 e 0.500 0.020 l 0.350 0.450 0.014 0.018 w-type 16l qfn 3x3 package note : the configuration of the pin #1 identifier is optional, but must be located within the zone indicated. det ail a pin #1 id and tie bar mark options 1 1 2 2

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