www.belling.com.cn 1 1.2a step-down dc-dc converter b l8516 description BL8516 is a current mode pwm stepdown dcdc converter, which has an internal 2a power switch. it has the wide input voltage range of 3.6v to 20v, so it can suit for regulatingawidevarietyofpowersource. BL8516 use bipolar technology and make of a pwm control circuit, a reference voltage unit, an error amplifier, a protection circuit, chip enable circuit, and under voltage lockout circuit. a low ripple, high efficiency stepdown dcdc converter can be easily composed of this ic with only several externalcomponents,oraninductor,adiode and capacitors. output voltage can be adjustedwithexternalresistors. the BL8516 has the cyclebycycle current limit circuit; current limiting provides protection against shorted output. the low current (<1ua) shutdown provides complete output disconnect, enabling easy power managementinbatterypoweredsystems. features rangeofinputvoltage:3.6v~20v builtinnpnswitch <1ashutdowncurrent oscillationfrequency:1.2mhz highefficiency:90% highaccuracyoutputvoltage: 2% lowtemperaturedriftcoefficientof outputvoltage:type: 100ppm/c operatingtemperaturerange:40 ~85 demoboardavailable applications powersourceforhandheld communicationequipment,cameras, videoinstrumentssuchasvcrs, camcorders. powersourceforbatterypowered equipment. powersourceforhouseholdelectrical appliance orderinginformation BL8516 1 2 3 code description 1 temperature&rohs: c:40~85 c,pbfreerohsstd. 2 packagetype: d8:sop8 3 packingtype: tr:tape&reel(standard) pinconfiguration product classification BL8516 cd8tr marking hfxx yybzz hf:product code xx:output voltage adjustable yy:lotno. b:fabcode zz:datecode hfxx yybzz 1 2 3 4 5 6 7 8
www.belling.com.cn 2 BL8516 pindescription blockdiagram absolutemaximumrating supplyvoltage 25v boostpinvoltage 35v boostpinaboveswpin 25 cepinvoltage C0.3vtovin+0.3v fbpinvoltage C0.3vto6v operatingambienttemperaturerange C25cto85c storagetemperaturerange C40cto150c leadtemperature(soldering,10sec) 260c thermalresistance: ja 150c/w pin no. symbol description 1 boost boostpin 2 vin powersupplypin 3 sw switchingnode:pwmoutputconnectiontoinduc tor. 4 gnd groundpin 5 fb pinforfeedbackvoltage 6 nc notconnected 7 ce chipenablepin(activewithh) 8 nc notconnected
www.belling.com.cn 3 BL8516 electricalcharacteristics (testconditionisin25oc,vin=12v,vboost=17v,un lessotherwisenoted.) symbol item conditions min. typ. max. unit vuvlo undervoltagelockout 3.35 3.6 v vfb feedbackvoltage 1.225 1.25 1.275 v ifb fbpinbiascurrent vfb=1.25v 150 600 na iq quiescentcurrent vfb=1.3v 2 ma quiescentcurrentin shutdown vce=0v 2 ua vfb/ v referenceline regulation vin=5vto20v 0.08 %/v vfb/ t feedbackvoltage temperaturecoefficient 25 topt 85 100 ppm/ fosc_max oscillatorfrequency vfb=1.1v 1.2 mhz foscth frequencyshift thresholdonfbpin fsw=700k 0.44 v dmax maxdutycycle 88 % ilimit switchcurrentlimit vin=10v 2.5 a vcesat switchsaturation voltage isw=300ma 220 350 mv isw switchleakagecurrent 1 ua iceh cehinputcurrent vce=3v 6.5 15 a icel celinputcurrent vce=0v 0.03 0.1 a vceh cehinputvoltage vin=12v 1.8 v vcel celinputvoltage vin=12v 0.4 v typicalapplication r1 u1 boost vin sw gnd fb nc ce nc c1 c2 c3 r2 d3 l1 vin ce vout d1
www.belling.com.cn 4 BL8516 demoboardbom table1billofmaterials no. reference type specification note 1 c1 capacitor tantalumcapacitor;25v/47uf;smd 2 c2 capacitor tantalumcapacitor;25v/22uf;smd 3 c3 capacitor mlcc10nf;smd0805 4 d1 diode ss34;40v,3a;smd 5 d3 diode 1n4148;75v;100ma;smd1206 6 l1 inductor 10uh;3a;smd,shielding 7 ic1 ic BL8516;smdsop8 8 r1 resistor smd0805;1% note1 9 r2 resistor smd0805;1% note1 note1: for vout=5v, r1 is 9.1k and r2 is 3k. for vout=3.3v, r1 is 3.3k and r2 is 2k. demoboardmeasurement load regulation (vout=5v) 0 1 2 3 4 5 6 0 200 400 600 800 1000 1200 output current(ma) output voltage(v) vin=7v vin=12v vin=20v efficiency vs. load current (vout=5v) 0 10 20 30 40 50 60 70 80 90 100 0 200 400 600 800 1000 1200 output current(ma) efficiency (%) vin=7v vin=12v vin=20v load regulation (vout=3.3v) 0 1 2 3 4 0 200 400 600 800 1000 1200 output current(ma) output voltage(v) vin=7v vin=12v vin=20v efficiency vs. load current (vout=3.3v) 0 10 20 30 40 50 60 70 80 90 100 0 200 400 600 800 1000 1200 output current(ma) efficiency (%) vin=7v vin=12v vin=20v
www.belling.com.cn 5 BL8516 quiescent current vs. supply voltage 0 1000 2000 3000 0 5 10 15 20 supply voltage (v) quiescent current (ua) feedback voltage vs.supply voltage 1.20 1.22 1.24 1.26 1.28 1.30 5 10 15 20 supply voltage(v) feedback voltage(v) feedback voltage vs.temperature 1.20 1.22 1.24 1.26 1.28 1.30 -50 -25 0 25 50 75 100 temperature feedback voltage(v) frequency vs.temperature 1.00 1.05 1.10 1.15 1.20 1.25 1.30 -50 -25 0 25 50 75 100 temperature(oc) frequency(mhz) applicationinformation inductor selection and maximum output current thedutycycleoftheinternalswitchis: d=(vout+vd)/(vinCvsw+vd) inwhichvdistheforwardvoltagedropofthe catchdiode(d1)andvswisthevoltagedrop oftheinternalswitch.thevalueofdutycycle atfullloadcurrentisofspecialinterest,when valuesofvswandvdcanbothassumedto be0.4v. since BL8516 has a maximum guaranteed dutycycleof88%,theminimuminputvoltage is limited for a particular value of output. when the switch is off, the voltage drop acrosstheinductorisequaltooutputvoltage plus the catch diode drop. therefore the peaktopeak ripple current in the inductor canbederived: ? il=(1Cd)(vout+vd)/(l?fosc) in which fosc is the switching frequency and l is the value of the inductance. the average inductor current is equal to the output current and the peak inductor current isthesumoftheoutputcurrentandonehalf oftheripplecurrent: ilpk=iout+il/2 this current has to be kept below the maximum allowed switch current (ilimit) for outputregulation.typicalvaluesofilimitare above 2.5a and themaximum output current is iout(max)=ilimitCil/2 if the ripple current is small, then the availableoutputcurrentisclosetotheswitch current limit. it is recommended that the inductorvaluebechosensuchthatthepeak
www.belling.com.cn 6 BL8516 topeakinductorripplecurrentisequaltoone thirdofswitchcurrentlimit.hencethevalue of inductance and the maximum output currentcanbeexpressedas: l=3(1Cd)(vout+vd)/(ilimit?fosc) and iout(max)=(5/6)ilimit from above discussion it is derived that the switch current limit is dependant on the duty cycle,whichalsoisafunctionofinputvoltage. for a specific application, one can calculate the value of inductance and the range of available output current according to the maximumandminimumallowedinputvoltage values. capacitor selection the input capacitor (c1) supplies the ac component of the current drawn by the converter. a 10uf ceramic capacitor is sufficientinmostcases. incasetheapplicationcircuitryhasrelatively large parasitic parameters (most often caused by long wires or filter components), additional bulk input capacitance may be required. for highpower applications it is suggested to increase the input capacitance to100uf. the output capacitor filters the square wave generated by the chip to produce the dc output and stores energy to supply transient loads as well as stabilizes the control loop. while for most switching mode converters, the outputripple ismainly determined by the equivalent series resistance (esr) of the outputcapacitor,theBL8516scontrolloopis independent on the output capacitors esr forstableoperation.ifalowesrcapacitoris selected, for example ceramic capacitor, output ripple can be estimated by the followingequation: vripple=il?[esr+1/(8?fosc?c2)] the output capacitor must have an energy capacity larger than the inductorotherwise thetransferofenergyfromtheinductortothe output can cause large overshoot. for a 5% overshoot, the minimum value of the output capacitorcanbepresentedas: 2 ) / ( 10 2 vout ilimit l c 3 good transient performance also requires large output capacitance. the above equation also offers a good starting point for obtaintheproperoutputcapacitancevalueto achievesatisfactoryperformance. application engineers can start with the datasheetrecommendedvalue. the high performance (low esr), small size and robustness of ceramic capacitors make them the preferred type for BL8516 applications. one needs keep in mind that not all ceramic capacitors are the same. manyofthehighervaluecapacitorsusepoor dielectrics with hightemperature and voltage coefficients. catch diode schottky diode with 3a current rating is recommendedforthecatchdioded1. boost pin considerations in the application circuit shown in the cover page,capacitorc3anddioded2areusedto boostinputvoltagetoahigherlevel.inmost cases a 10nf capacitor and a fast switching diode are suitable for this purpose. the voltage at the boost pin must be at least 2.5v higher than the sw pin for best efficiency. theminimumoperatingvoltageofanBL8516 application is limited by the under voltage lockout (< 3.6v) and by the maximum duty cycleasoutlinedabove. forproperstartup,theboostcircuitalsolimits the minimum input voltage. if the input voltage is ramped slowly, or the BL8516 is turned on with its ce pin when the output is alreadyinregulation,thentheboostcapacitor maynotbefullycharged.becausetheboost capacitorischargedwiththeenergystoredin the inductor, the circuit will rely on some minimumloadcurrenttogettheboostcircuit running properly. this minimum load will dependoninputandoutputvoltages,andon the arrangement of the boost circuit. the minimum load generally goes to zero once the circuit has started. in many cases the discharged output capacitor will present a loadtotheswitcher,whichwillallowittostart.
www.belling.com.cn 7 BL8516 packageline package sop8 devicesperreel 2500pcs unit mm packagespecification symbol dimension (mm) symbol dimension (mm) min nom max min nom max a - - 1.77 d 4.7 4.9 5.1 a1 0.08 0.18 0.28 e 5.8 6 6.2 a2 1.2 1.4 1.6 e1 3.7 3.9 4.1 a3 0.55 0.65 0.75 e 1.27bsc b 0.39 - 0.48 l 0.5 0.65 0.8 b1 0.38 0.41 0.43 l1 1.05bsc c 0.21 - 0.26 q 0 - 8
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