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bw 7381 universal high brightness led driver rev.1.4 jan. 2013 ! features z universal rectified 90vac to 264vac input voltage range z built-in active power factor correction te c h n i q u e z low thd, meet with iec-61000-3-2 class-c z high efficiency application z built-in output short circuit protection with auto-recovery z built-in output over voltage protection with auto-recovery z built-in gate clamp z cycle-by-cycle current limit z fail-safe, output is not subjected to line voltage if the mosfet fails. z excellently accurate constant current z very tight line and load regulation z constant off-time z buck or buck-boost configuration applications z ac/dc led driver application z dc/dc led driver application z signage and decorative led lighting z residential lighting description the bw 7381 is a controller for off-line led converter. the bw 7381 operate with constant off-time, peak current mode control with active power factor correction function. the controller senses real-time switch current to cycle-by-cycle current limit. cycle-by-cycle current limit at the cs pin ensure a safe operation during short-circuit at the output. it can be configured in either buck-boost (figure1) or buck (figure2) application circuit. the driver output voltage is limited to 19v to protect external power mosfet. the controller also monitors integrated actual led current to perform the excellent line and load regulation. the controller makes the inductor current to follow the shape of input voltage to perform high power factor and low thd solution. the bw 7381 provides complete protection features such as short-circuit and open-circuit protection. order information pin configurations (top view) bw 7381 - s8 r bruckewell circuit t yp e s8: sop-8 shipping: r: tape & reel
bw 7381 universal high brightness led driver pin descriptions pin name pin description cs switch current sense pin. gnd ic ground and reference. flt actual output current sensing pin. comp output pin of error amplifier. rt constant off-time setting. vin ac-line voltage sensing pin. vdd power supply pin for all internal circuit. out power mosfet driver output. typical application circuits buck-boost topology figure 1 rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver buck topology ac+ ac r gnd 2 cs_flt 3 vin 6 rt 5 comp 4 vdd 7 out 8 cs 1 BW7381 ic_gnd ic_gnd ic_gnd led+ r ic_gnd ic_gnd ic_gnd ic_gnd ic_gnd gnd c1 l2 r1 v r line gnd v r line led r10 r11 r12 zd1 d2 r9 e1 l1 r2 r5 r3 c4 c6 r6 r7 q1 c5 c3 c2 d1 figure 2 rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver absolute maximum ratings (note 1) parameter symbol range unit power supply pin v dd - 0 . 3 t o 3 0 v cs voltage to gnd v cs - 0 . 3 t o 5 v flt voltage to gnd v flt - 0 . 3 t o 5 v comp voltage to gnd v comp - 0 . 3 t o 5 v vin voltage to gnd v in - 0 . 3 t o 5 v rt voltage to gnd v rt - 0 . 3 t o 5 v out voltage to gnd v out - 0 . 3 t o 3 0 v operating junction temperature rang t j - 4 0 t o + 1 5 0 c operating ambient temperature rang t opa - 4 0 t o + 8 5 c storage temperature rang t stg - 6 5 t o + 1 5 0 c lead temperature (soldering 5 sec) t lead 260 c power dissipation @t a =25 c p d 0 . 4 w thermal resistance junction to ambient (note 2) ja 160 c/w esd rating, human body mode (note 3) v esd 2 k v recommended operating conditions (note 4) parameter symbol operation conditions unit supply voltage v dd 2 0 v junction temperature range t j -20 to +125 c ambient temperature range t a -20 to +85 c note 1: stresses listed as the above absolute maximum ratings ma y cause permanent damage to the device. these are for stress ratings. functional operation of the device at these or any othe r conditions beyond those indicat ed 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: thermal resistance is specified with the component mounted on a low effective thermal conductivity test board in free air at t a =25 c. note 3: devices are esd sensitive. handing precaution recommended. note 4: the device is not guaranteed to func tion outside its operating conditions. rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver block diagram figure 3 rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver electrical characteristics t a = 25c, unless otherwise specified. parameter symbol condition min typ max unit vdd section start-up threshold v dd(st) 17 18 19 v under voltage lockout threshold v dd(uvlo) 7 . 5 8 . 5 9 . 5 v over voltage protection v ovp 27 28 29 v start-up current i inst v dd(st) - 1v 42 60 78 ua operating current i ddq 560 800 1040ua current limit section maximum current sense voltage v cspk 0.67 0.7 0.74 v propagation delay t dly 70 ns output current integration reference voltage v iref 0.2 v error amplifier section transconductance g m 84 120 156 us maximum sink current i sink 53 ua maximum source current i source 58 ua line sensing section source current i se(vin) 375 ua constant off time section regulated voltage v rt 0.95 1 1.05 v off-time setting range t off r rt = 136k~17k 5.73 40.4us constant off-time t off(lv) rt = 50k, 85vac~150vac13.5 15 16.5 us t off(hv) rt = 50k, 180vac~300vac18.9 21 23.1 us driver section rising time t rise v dd =12v, c_load=1nf 48 ns falling time t fail v dd =12v, c_load=1nf 31 ns clamped voltage v gate 1 9 v rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver application information 1. function description the bw 7381 is a high performance controller which monitors actual output current. these results bw 7381 enable tight line and load regulation. the bw 7381 uses constant off-time peak current mode control to control the switching current in the mosfet. at initial, vdd capacitor charged through start-up resistor until it achieves 18v. then bw 7381 turns-on the mosfet and make its shape of p eak current flow input sine wave. this performs high power factor and low total harmonic distortion. the output current flow through a current sensing resistor and feedback to flt pin. the controller always adjusts the amplitude of current command base on the potential of flt pin. once the peak current reaches the current command, controller turns off the mosfet. the resistor connected at rt pin determines the off-time. at the switching on-time, controller senses and limits the maximum switch current by cs pin. this ensures the current in mosfet be limited in safe operating area. the bw 7381 built-in output short-circuit and over-voltage protection. while the mosfet turns off at the off-time, the vdd capacitor can get charge by output voltage, and contro ller can set output over voltage protection threshold by specified zener diode. if the led string is open, the output voltage will be boost over the designed level until the vdd arrive to 28v. the bw 7381 goes into over-voltage protection and latches the mosfet. the controller starts up the system again while the vdd falls to 8.5v (uvlo). therefore, the converter auto-recovery output while the output open circuit condition removed. in case of output short-circuit condition. the vdd capac itor cannot get charge from output voltage. so, the converter repeats start-up and uvlo. however, the bw 7381 provides full protections such as ocp, ovp, gate-voltage clamp and cycle-by-cycle current limit. 2. pin detail 2-1. cs mosfet current sensing, use for cycle by cycle switch peak current control. 4 )(lim 7.0 r v i itl 2-2. gnd gnd is the reference node of internal circuit. 2-3. flt actual output current sensing, the signal feedback to error amplifier and compare with the internal reference voltage (0.2v). 2 2.0 r v i o 2-4. comp this is the output of the gm amplifier . connect with a suitable rc network to ground. rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver 2-5. rt constant off-time setup. for low-line, 85vac to 150vac ! : s k r toff t p 15 50 u : for high-line, 180 to 300vac ! : s k r toff t p 21 50 u : 2-6. vin sense signal input from the rectified line voltage. 2-7. vdd power supply for the controller during normal operation. the controller will start up when vdd reaches 18v (typical) and will shut-down when vdd voltage is below 8.5v (typical). a decoupling capacitor should be connected between the vdd and gnd pin as close as possible. 2-8. out gate drive for external mosfet switch. 3. design flow the typical application circuit for design flow below please refers to figure 1. 3-1. input signal sampling the bw 7381 sense input signal from rectified line voltage. vin pin in series with a resistor of 1.6m, r7 to system ground. it is need to pay attention to enough voltage rating for resistor. : mr 6.1 7 3-2. low pass filter for switch and output current sensing two r-c low pass filter are must for mosfet switch current sensing and actual output current sensing. the following is recommend values : : kr 7.4 3 fc p 1 4 : 100 5 r pfc 100 5 3-3. loop compensation place a capacitor of 2.2uf for compensation is recommend. fc p 2.2 6 3-4. output current sensing resistor the output current can be set up by a current sensing resistor, r 2 . the resistance is calculated following the equation below. o i v r 2.0 2 rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver 3-5. ovp threshold voltage the bw 7381 perform output over voltage protection though vdd pin. once vdd pin exceed in 28v, BW7381 turns off and latch out the mosfet swi tcher. the ovp threshold voltage can be set by the zener diode, zd 1 . vovpzd 28 1 3-6. vdd, supply current circuit at the beginning in start-up, the output voltage is not high enough to charge vdd capacitor. therefore vdd capacitor have to save enough energy for ic operating bias during start-up. to determine the capacitance, we need to calculate the ic opera ting current, idd first. ma freq cissidd 5.120 uu# in general, assume the vdd capacitor need to keep enough energy for 50ms. then the capacitance can be calculated. vv msidd c 5.818 50 2 u t nfc 100 3 place the vdd capacitor c 2 and bypass capacitor c 3 as close to ic as possible. morevoer, a current spike filter resistor r11 is suggest (10 : ~22 : ) to place between vdd and c3. 3-7. start-up resistor at the initial stage, the vdd capacitor get charge through start-up resistor towards the start-up threshold voltage. the smaller start-up resistor the larger power dissipation. the larger start-up resistor the longer charge time. 18 2)arg( 32 1 u u t cc vacecht r 3-8. off-time setting the duty cycle in buck-boost converter is a function of vin and vo. o o pk vvac v duty 2 )( the off-time can be set manually by adjusting the size of an external resistor (rt). the bw 7381 automaticall adjusts the off-time with the line voltage (vac). to calculat the operating off-time and rt, the maximum switching frequency at peak of line cycle must be determined first. freq duty toff pk h )( 1 4.1 h l toff toff :u k s toff r h 50 21 6 p where : toff h is the off-time at high-line (180vac to 300vac), toff l is the off-time at low-line (90vac to 135vac), 3-9. power inductor assume a target efficiency to estimate input power and input peak current. k oo iv pin u 2 )( u vac pin i pkin rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver in buck-boost converter, the average of current flow in mosfet is equal to the input current. if given a ratio of maximum inductor current ripple to maximum inductor peak current, ! j l 0j l(pk) /! then the inductor peak current can be estimated by the equation: )( )( )( )( 2 2 pk pkl l pkin pkl duty i i i i u ? ? 1 ? ' the maximum inductor current ripple, j l is : )( )( pkl l pkll i i ii ' u ' from the basic inductor equation, the inductance is : toff i v l l o u ' follow the equations above, the inductance and maximum inductor current can be computed. the magnetic design of the inductor must ensure that there is a sufficient flux density margin to avoid saturation with operating current being applied. 3-10. switch current sensing resistor the bw 7381 sense switch current from cs pin to provide cycle-by-c ycle current limit. while the cs pin goes execss of 700mv, the bw 7381 force mosfet switcher turn off. design the peak inductor current to 75 percent of switcher current limit is recommend. )( 4 53.0 peakl i v r 4 )(lim 7.0 r v i itl rev.1.4 jan. 2013 !
bw 7381 universal high brightness led driver package outline dimensions

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