www.belling.com.cn 1 high efficiency 1 /1.5 charge pump 4-channels led driver b l858 7 description BL8587 is a low noise, high efficiency, and constant frequency charge pump dc/dc converter for white led application. the operationfrequencyis1mhz. BL8587 works in load switch (1 ) and fractional(1.5 )modeswithfourindependent control outputs, each channel can provide 20maconstant currentpreciselyfrom a 2.8v to 5.5v supply. only two external 1 m f and two0.47 m fcapacitorsarerequiredtobuilda compactandlowcostpowersupplysolution. BL8587usesenpinforsimpleon/offcontrol and single wire serial pulse dimming in 16 steps. a low current shutdown feature disconnects the load from v in and reduces quiescentcurrenttolessthan1a. features inputrange:2.85.5v 1%ledcurrentaccuracy 20madrivercapacityeachchannel auto1 /1.5 modeswitchover pwmdimmingcontrol serialpulsedimmingcontrolinlinear16 steps shortcircuitprotection thermalshutdown 1mhzconstantswitchingfrequency 3mm 3mmqfnpackage application programmablecurrentsinks whiteledbacklighting cellphonesandsmartphones pdas,digitalcameras,andcamcorders color(rgb)lighting typicalapplicationcircuit BL8587
www.belling.com.cn 2 BL8587 pindiscriptions pinno. symbol description 1 nc noconnection 2 nc noconnection 3 d4 channel4sinkcurrentinput 4 d3 channel3sinkcurrentinput 5 d2 channel2sinkcurrentinput 6 d1 channel1sinkcurrentinput 7 gnd signalground 8 vout chargepumpoutputtodriveloadcircuit,a1fcap acitorshouldbeusedtoshort thispintoground. 9 c2+ flyingcapacitor2positiveterminal.connecta1f capacitorbetweenc2+and c2. 10 c1+ flyingcapacitor1positiveterminal.connecta1f capacitorbetweenc1+and c1. 11 c1 flyingcapacitor1negativeterminal. 12 c2 flyingcapacitor2negativeterminal. 13 vin powersupplyinput,a1 m fcapacitorisrequiredtoconnectthispintogrou nd. 14 pgnd powerground 15 nc noconnection 16 en enablepinandcanusethispintoprogramth esinkcurrent. pinconfiguration vin vinvin vin gnd gndgnd gnd en enen en nc ncnc nc nc ncnc nc d dd d1 11 1 d dd d2 22 2 d dd d3 33 3 d dd d4 44 4 c cc c1 11 1- -- - c cc c1 11 1+ ++ + c cc c2 22 2- -- - c cc c2 22 2+ ++ + vout vout vout vout pgnd pgnd pgnd pgnd nc ncnc nc 16 1616 16 15 1515 15 l l l l g g g g y y y y y y y y n n n n z z z z z z z z 1 11 1 2 22 2 3 33 3 4 44 4 5 55 5 6 66 6 7 77 7 9 99 9 10 1010 10 11 1111 11 12 1212 12 13 1313 13 14 1414 14 8 88 8 topviewqfn3mm 3mm orderinginformation productno orderingnumber pinpackage devicesper reel temperaturerange&rohs BL8587 BL8587cjktr 3*3qfn16 3000 40~85 c&pbfree absolutemaximumrating item description value unit vin inputsupplyvoltage 0.36 v iomax maximumloadcurrent 100 ma tj operatingjunctiontemperaturerange 40150 c marking lg:productcode yy:lotno. n:fabcode zz:datecode
www.belling.com.cn 3 BL8587 electricalcharacteristics c in =c out =1 m f,c 1 =c 2 =0.47 m f,t a =25 c,unlessotherwisenoted. symbol description condition min typical max unit v in supplyvoltagerange 2.8 5.5 v v_ uvlo undervoltagelockoutthreshold 2.5 2.8 v i q quiescentoperatingcurrent 1 mode/noloadcurrent 0.3 0.5 ma 1.5 mode/noloadcurrent 6 i sd shutdowncurrent en=0 1 m a i led sinkcurrentaccuracy i set =20ma 10 +10 % v th 1.5 modeto1 mode transitionthreshold 3.7 v r out openloopoutresistance 1xmode,(vinvout)/iout 2.2 w 1.5xmode,(1.5vin vout)/iout 5 v en enablevoltage logichighvoltage 1.2 v logiclowvoltage 0.4 t en _ pulse thepositiveandnegativepulse widthofenpin dimmingcontrol 4 20 m s v dropout dpindropoutvoltage 100%ledcurrentsetting (note1) 120 mv i short outputshortcurrent shortoutputtoground 100 ma f osc oscillatorfrequency 0.7 1 1.3 mhz tsd thermalshutdowntemperature 150 c t_ h thermalshutdownhysteretic 30 c note1: dropout voltage is defined as the d pin to g nd voltage at which current into d pin drops 10% fr om the value at v d =0.2v . blockdiagram
www.belling.com.cn 4 BL8587 typicalcharacteristics led curent vs dropout voltage 0 5 10 15 20 25 0 50 100 150 200 250 dropout voltage(mv) led current(ma) led current vs pulse number 0 5 10 15 20 25 0 4 8 12 16 pulse number led current(ma) led current matching vs input voltage (20ma/led) 14 16 18 20 22 24 26 28 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 input voltage(v) led current(ma) d1 d2 d3 d4 led current matching vs input voltage (10ma/led) 7 8 9 10 11 12 13 14 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 input voltage(v) led current(ma) d1 d2 d3 d4 quiescent current vs input voltage 0 1 2 3 4 5 6 2.5 3.5 4.5 5.5 input voltage(v) quiescent current(ma) 1.5x mode 1x mode
www.belling.com.cn 5 BL8587 operationwaveforms fig. 1 startup from en pin fig. 2 shutdown from en pin fig. 3 operating at 1.5x mode with 100% brightness fig. 4 operating at 1x mode with 100% brightness en led current led current en input voltage ripple output voltage ripple led current input voltage ripple output voltage ripple input current
www.belling.com.cn 6 BL8587 detaildescription startup sequence the BL8587 starts to work only when vin powered on and the en pin became high after a delay, the delay time is at least 4us. en pin is not allowed to connect to vin directlyorkeepitfloating. the BL8587 starts with 1x mode, the output follows closely to the supply voltage. if the average voltage of pin d1 to d4 falls below 0.25v the ic switches to 1.5x mode, and it can automatically switch back to 1x mode whentheinputvoltageishigherthan3.7v. pwm dimming control ifthefrequencyofthepwmsignaltotheen pin is less than 5khz, the average led currentisproportionaltothedutycycleofthe pwm signal, and the en works as a simple on/offcontrol.ahighlevelturnsonandalow shuts down the leds. there is a delay time betweentheinputpwmsignalandtheoutput ledcurrentwaveform,asshowninfig.5,the t d isabout20us. i_led 20ma td=20us on duty td=20us en fig. 5 pwm dimming control en dimming control the leds brightness can also be controlled bythepulsesappliedtotheenpin,referto the fig. 6. inside the device there is a 4bit counter connecting to the en pin. the led current can be programmed up to 16 levels depends on the number of rise edges of the input waveform. a high level input (1) with pulsewidthwiderthan20usisregardedasa signal to stop the buildin counter. the time between two wide high levels (more than 20us) is a counting period. when some rise edgesoccurbetweentwohighlevelpulsesof 20us, the equation as shown below can calculate the active pulse number, called code_no. ) 16 , ( _ n mod no code = , intheequation,nisthenumberofriseedges of the input waveform and mod function returnstheremainderofndividedby16.for example,ifn=0,16,orotherintegralmultiple of16,themodfunctionreturnsavalueof0,if n=1,17orotherintegralmultipleof16plus1, themodfunctionreturnsavalueof1,andso on. the relationship between leds brightness and the code_no is listed as the following table. codeno i set /20ma codeno i set /20ma 0 0 8 8/15 1 1 9 7/15 2 14/15 10 6/15 3 13/15 11 5/15 4 12/15 12 4/15 5 11/15 13 3/15 6 10/15 14 2/15 7 9/15 15 1/15 the frequency of the input pulse should be lowerthan100khz,andthewidthofthehigh levelandlowlevellargerthan4ustoprevent falsetrigger. code_no=1 code_no=4 iset/20ma=15/15 20us 20us en i_le d iset/20ma=12/15 fig. 6 linear current dimming control
www.belling.com.cn 7 BL8587 short circuit protection if the voltage difference between vout pin andanyofadpinexceeds1v,forexample, a led is shorted in the circuit, the corresponding channel will be shutdown internally by the ic. connect all unused leds to vout to avoid the accuracy reductionofthethresholdofswitchingto1.5x, anditalsoavoidswastingbatterycurrent. if the vout is shorted to ground, the BL8587 will stop operating and keep a constant sourcecurrentofabout100mauntiltheshort circuitisremoved. thermal protection whenthedevicetemperatureexceeds150c the driver enters a thermal protection shutdown mode. the ic resumes normal operation once the temperature drops by about30cto120c. led selection leds with lower v f are recommended. from the efficiency perspective.itkeeps the driver in the 1x mode longer hence helps improve the efficiency and extends battery life. for example, a white led with a v f of 3.2v can keep the device working in the 1x mode for lowersupplyvoltageof0.3vthanaledwith v f of 3.5v. for the BL8587, the led with dropoutlowerthan3.4visadequate. external component thedriverrequirestwoexternal1fceramic capacitors for decoupling input, output, and forthechargepump.bothcapacitorstypeof x5randx7rarerecommendedfortheled driverapplication.inchargepumpmodes,the input current ripple is kept minimal. an input bypass capacitor of 1f is sufficient. in 1x mode, the device operates linearly and does notintroduceswitchingnoisetothesupply. layout consideration duetoitshighswitchingfrequencyandhigh transientcurrent,carefulconsiderationof pcblayoutisnecessary.theinputcapacitor (c in )andthedevice,aswellasthegroundof c in andc out shouldbeplacedascloseas possible.toachievebestperformance,itis recommendedtominimizethedistance betweencomponents.maximumtracewidth isrecommendedforconnection.makesure eachdeviceconnectstoimmediateground plane.theuseofmultipleviaimprovesthe packageheatdissipation.
www.belling.com.cn 8 BL8587 packageinformation package qfn3x316 devicesperreel 3000 unit mm
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