bp 2831a non - isolated buck offline led driver bp 2831a_en _ds_rev. 1.0 www.bpsemi.com 1 bps confidential C customer use only description the bp 2831a is a high precision buck constant current led driver. the device operates in critical conduction mode and is suitable for 85vac~265vac univers al input offline led lighting. the bp 2831a integrates a 500v power mosfet. with patent pe nding mosfet drivi n g technique, the operating current of the ic is very low . s o it doesnt need the auxiliary winding for supplying the chip. i t can achieve excellent constant current performance with very few external components , so the system cost and si ze are minimized . the bp 2831a utilizes patent pending current control method. it can achieve precise output current and excellent line regulation. the driver operates in critical conduction mode , t he output current does not change with the inductance and led output voltage. the bp 2831a offers rich protection functions to improve the system reliability, including led open circuit protection, led short circuit protection, vcc under voltage protection, cs resistor short circuit protection and thermal regulati on function . features ? critical conduction mode operation ? internal 500v power mosfet ? no auxiliary winding ? ultra low operating current ? 5% led output current accuracy ? led open protection ? led short protection ? current sensi ng resistor short protection ? vcc unde r voltage protection ? thermal regulation function ? available in sop - 8 package applications ? led candle light ? led bulb ? other led lighting typical application figure 1. typical application circuit for bp 2831a ?? b p 2 8 3 1 a a c n c c s g n d c s d r a i n 8 7 6 5 1 2 4 v c c r o v p d r a i n 3 free datasheet http://www.datasheetlist.com/
bp 2831a non - isolated buck offline led driver bp 2831a_en _ds_rev. 1.0 www.bpsemi.com 2 bps confidential C customer use only ordering infor mation part number package operating temperature package method marking bp 2831a sop8 - 40 to 105 tape 2 , 5 00 piece/roll bp 2831a xxxxxy wxyy pin configuration and marking information fig ure 2. pin configuration pin definition pin no. name description 1 gnd ground 2 rovp over voltage protection setting pin. connect a resistor to gnd 3 nc no connection. should be connected to gnd(pin1) 4 vcc power supply pin 5 ,6 drain internal hv powe r mosfet drain. 7 , 8 cs current sense pin . connect a sens e resistor between this pin and gnd pin. xxxxxy: l ot c ode w: sign x: year yy : week ?? d r a i n g n d c s d r a i n c s r o v p n c v c c b p 2 8 3 1 a x x x x x y w x y y free datasheet http://www.datasheetlist.com/
bp 2831a non - isolated buck offline led driver bp 2831a_en _ds_rev. 1.0 www.bpsemi.com 3 bps confidential C customer use only absolute maximum ratings (note1) symbol parameters range units i cc_max vcc pin maximum sink current 5 ma drain internal hv mosfet drain voltage - 0 .3 ~ 500 v cs curre nt sense pin input voltage - 0.3 ~ 6 v rovp over - voltage setting pin voltage - 0.3~6 v p dmax power dissipation (note 2) 0.45 w ja thermal resistance (junction to ambient) 145 j operating junction temperature - 40 to 150 stg stora ge temperature range - 55 to 150 note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. under recommended op erating conditions the device operation is assured, but some partic ular parameter may not be achieved. the electrical characteristics table defines the operation range of the device, the electrical characteristics is assured on dc and ac voltage by test program. for the parameters witho ut minimum and maximum value in the ec table, the typical value defines the operation range, the accuracy is not guaranteed by spec. note 2: the maximum power dissipation decrease if temperature rise, it is decided by t jmax , ja , and environment temperature (t a ). the maximum power dissipation is the lower one between p dmax = (t jmax - t a )/ ja and the number listed in the maximum table. note 3: human body mode, 100pf capacitor discharge on 1.5 k resistor recommended operation conditions symbol parameter range unit i led 1 output led current @ vout= 72 v (input voltage 176v 265v) 160 ma i led 2 output led current @ vout= 36 v (input voltage 176v 265v) 220 ma v led min minimum led loading voltage >15 v ?? free datasheet http://www.datasheetlist.com/
bp 2831a non - isolated buck offline led driver bp 2831a_en _ds_rev. 1.0 www.bpsemi.com 4 bps confidential C customer use only electrical characteristics ( notes 4, 5) (unless otherwise specified, v cc =15 v and t a =25 ) symbol parameter conditions min typ max units supply voltage section v cc_clamp v cc clamp voltage 1ma 1 6.8 v v cc_on v cc turn on threshold v cc rising 1 3.8 v v cc_uvlo v cc turn off threshol d v cc falling 9 v i st v cc startup current v cc = v cc - on - 1v 120 180 ua i op v cc operating current f op =70khz 100 150 ua current sense section v cs_th threshold voltage for peak current limit 388 400 412 mv v cs_short threshold voltage for peak current limit when output short output short 200 mv t leb leading edge blanking time for current sense 350 ns t delay switch off delay time 200 ns internal time control section t off_min minimum off time 4.5 us t off_max maximum off time 240 us t o n_max maximum on time 40 us v rovp rovp pin voltage 0.5 v mosfet section r ds_on static drain - source on - resistance v gs =15v/i ds =0.4a 14 bv dss drain - source breakdown voltage v gs =0v/i ds =250ua 500 v i dss power mosfet drain leakage current v gs =0v /v ds =500v 1 ua thermal regulation section t reg thermal regulation temperature 150 note 4: production testing of the chip is performed at 25c. note 5: the maximum and minimum parameters specified are guaranteed by test, the typical value are gua ranteed by design, characterization and statistical analysis ?? free datasheet http://www.datasheetlist.com/
bp 2831a non - isolated buck offline led driver bp 2831a_en _ds_rev. 1.0 www.bpsemi.com 5 bps confidential C customer use only internal block diagram figure 3. bp 2831a internal block diagram application information the bp 2831a is a high performance non - isolated buck converter specially designed for le d lighting. the device integrates a 500v power mosfet. with very few external components, the converter achieves excellent constant current control. and it does not need auxiliary winding for powering the ic or voltage sensing, hence the sys tem size and cost is greatly reduced. start up after system powered up, the vcc pin capacitor is charged up by the start up resistor. when the vcc pin voltage reaches the turn on threshold, the internal circuits start operating. t he bp 2831a integrates a 17 v zener diode to clamp the vcc voltage. due to the ultra - low operati ng current , the auxiliary winding is not needed to supply the ic. constant current control cycle by cycle current sense is adopted in bp 2831a , the cs pin is connected to the current sense comparator, and the voltage on cs pin is compared with the i nternal 400mv reference vo ltage . t h e mosfet will be switched off when the voltage on cs pin reaches the threshold. the cs comparator includes a 350ns leading edge blanking time. the peak inducto r current is given by: where, r cs is the current sense resistor value. the current in led can be calculated by the equation: ?? v c c u v l o + - - r e s e t 1 4 v 9 . 0 v c s + - c u r r e n t s e n s e g n d c c & l o g i c c o n t r o l o v p l e d 4 0 0 m v d r a i n h v m o s f e t o c p o t p v c c r o v p 1 7 v ) ma ( r 400 i cs pk ? free datasheet http://www.datasheetlist.com/
bp 2831a non - isolated buck offline led driver bp 2831a_en _ds_rev. 1.0 www.bpsemi.com 6 bps confidential C customer use only where, i pk is the peak current of the inductor . inductor selection the bp 2831a works under inductor current critical conduction mode. when the power mofet is switched on, the current in the inductor rises up from zero, the on time of the mosfet can be calculated by the equation: where, l is the inductance value v in is the dc bus voltage after the rectifie r bridge v led is the voltage on the led after the power mosfet is switched off, the current in the inductor decreases . w hen the inductor current reaches zero, the power mosfet is turned on again by ic internal log ic. the off time of the mosfet is given by: the inductance can be calculated by the equation: t he f is the system switching frequency , which is proportional to the input voltage. so t he minimum switching frequency is set at lowest input voltage, and the maximum switching frequency is set at highest input voltage. the minimum and maximum off time of bp 2831a is set at 4.5us and 240us, respectively. referring to the equation of t off c alcu lation , if the inductance is too small, the t off may be smaller than the minimum off time, system will operate in discontinuous conduction mode and the output current will be smaller than the designed value. i f the inductance is too large, the t off may be larger than the maximum off time, the system will operate in continuous conduction mode and the output current will be higher than the designed value. so it is important to choos e a proper induct ance . over voltage protection the o ver voltage protection ca n be programmed by the rovp pin resistor. the rovp pin voltage is 0.5v. when the led is open circuit , the output voltage increases gradually , and the demagnetization time gets shorter. the d emagnetization time at ovp ---- tovp can be calculated by the o pen circuit protection voltage : where vcs is the cs pin turn off threshold ( 400mv ) vovp is the open circuit protection voltage and then the rovp resistor value can be calculated by the equation: k ohm protection function the bp 2831a offers rich protection functions to improve the system reliability , i ncluding led open/short protection, cs resistor short protection, v cc under voltage protection, thermal regulation. when the led is open circuit , the system will trigger the over voltage protection and stop switching . wh en the led short circuit is detected, the system works at low frequency (5khz), and the cs pin turn ?? 2 i i pk led ? led in pk on v v i l t ? ? ? led pk off v i l t ? ? in pk led in led v i f ) v v ( v l ? ? ? ? ? vovp rcs vcs l tovp ? ? ? 6 10 * * 15 tovp rovp ? free datasheet http://www.datasheetlist.com/
bp 2831a non - isolated buck offline led driver bp 2831a_en _ds_rev. 1.0 www.bpsemi.com 7 bps confidential C customer use only off threshold is reduced to 200mv . s o the system power consumption is very low. at some catastrophic fault condition, such as cs resistor short ed or inducto r s aturated , the internal fast fault detection circuit will be triggered, the system stops switching immediately. after the system enters into fault condition, the vcc voltage will decrease until it reaches the uvlo threshold , t hen the system will re - star t again. if the fault condition is removed, the system will recover to normal operation . thermal regulation the bp 2831a integrates thermal regulation function. when the system is over temperature, the output current is gradually reduced; the output power and thermal dissipation are also reduced. the system temperature is regulated and the system reliability is improved. the thermal regulation temperature is set to 150 internally. pcb layout the following rules should be followed in bp 2831a pcb layout: b ypass capacitor the bypass capacitor on v cc pin should be as close as possible to the v cc pin and gnd pin. rovp pin the rovp resistor should be as close as possible to the rovp pin. ground path the power ground path for current sense should be short, and t he power ground path should be separated from small signal ground path before connecting to the negative node of the bulk capacitor. the area of power loop the area of main current loop should be as small as possible to reduce emi radiation, such as the i nductor, the power mosfet, the output diode and the bus capacitor loop. nc pin the nc pin should be connected to gnd ( pin1) . drain pin to i ncrease the copper area of drain pin for better thermal dissipation. however too large copper area may compromise em i performance. ?? free datasheet http://www.datasheetlist.com/
bp 2831a non - isolated buck offline led driver bp 2831a_en _ds_rev. 1.0 www.bpsemi.com 8 bps confidential C customer use only physical dimensions ?? free datasheet http://www.datasheetlist.com/
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