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rt84 9 7 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8497 - 01 july 2015 www.richtek.com 1 power mosfet integrated high efficiency bcm led driver controller for high power factor applications general description the RT8497 integrates a power mosfet and a boundary mode con troller. it is use d for step down converters by well controlling the internal mosfet and regulating a constant output current. the RT8497 features a zcs detector which keeps s ystem operating in bcm and obtaining excellent power efficiency, better emi performance. the RT8497 achieves high p ower factor correction (pfc) and low t otal harmonic distortion of current (thdi) by a smart internal line voltage compensation circuit which has minimized system component counts; saved both pcb size and total system cost. especially, the RT8497 can use a cheap simple drum core inductor in the system instead of an ee core to obtain high efficiency. the RT8497 is housed in a sop - 8 package. thus, the components in the whole led driver system can be made very compact. ordering information note : richtek products are : ? rohs compliant and compatible with the current requirements of ipc/jedec j - std - 020. ? su itable for use in snpb or pb - free soldering processes features ? built - in power mosfet ? support high power factor and thdi consideration applications ? programmable constant led current with highly ? precision current regulation ? extremely low quiescent current consumption and 1 ? ? true low system bom cost and economical floating buck converter solution ? unique programmable and pin for zvs setting to achieve best power efficiency ? universal input voltage range with off - line topology ? built - in over th ermal protection ? built - in over voltage protection ? output led string open protection ? output led string short protection ? output led string over current protection applications ? e27, par, light bar, offline led lights pin configurations (top view) sop - 8 r t 8 4 9 7 p a c k a g e t y p e s : s o p - 8 l e a d p l a t i n g s y s t e m g : g r e e n ( h a l o g e n f r e e a n d p b f r e e ) m o s f e t b u i l t - i n d e f a u l t : 5 0 0 v / 5 . 2 a : 5 0 0 v / 2 b : 5 5 0 v / 4 . 2 c : 5 5 0 v / 7 ? ? ? ? s g n d v c a n d s o u r c e v c c n c d r a i n d r a i n 2 3 4 5 6 7 8
rt84 9 7 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8497 - 01 july 2015 2 marking information functional pin description pin no. pin name pin function 1 s gnd ground of the chip. 2 vc close loop compensation node. 3 and next delay timing function control. 4 source internal power mosfet source connection. 5, 6 drain internal power mosfet drain connection. 7 nc no internal connection. 8 vcc supply voltage input of the chip. for good bypass, a ceramic capacitor near the vcc pin is required. function block diagram operation the RT8497 senses true average output current and keeps the system driving constant output current. the vc pin is the compensation node in this close loop system and dominates the frequency response. to stabilize the system and achieve better pfc / thdi, p roper selection of a compensation network is needed. r t 8 4 9 7 g s y m d n n r t 8 4 9 7 g s : p r o d u c t n u m b e r y m d n n : d a t e c o d e r t 8 4 9 7 g s r t 8 4 9 7 c g s y m d n n r t 8 4 9 7 c g s : p r o d u c t n u m b e r y m d n n : d a t e c o d e r t 8 4 9 7 c g s r t 8 4 9 7 b g s y m d n n r t 8 4 9 7 b g s : p r o d u c t n u m b e r y m d n n : d a t e c o d e r t 8 4 9 7 b g s r t 8 4 9 7 a g s y m d n n r t 8 4 9 7 a g s : p r o d u c t n u m b e r y m d n n : d a t e c o d e r t 8 4 9 7 a g s d r a i n r e g u l a t o r s g n d a n d s t a t e m a c h i n e v c c v c a e a + - + - 2 5 0 m v s o u r c e s o u r c e
rt84 9 7 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8497 - 01 july 2015 www.richtek.com 3 absolute maximum ratings (note 1) ? supply input voltage -------------------------------- -------------------------------- -------------------------------- 40 v ? drain to source voltage, v ds , (RT8497b) -------------------------------- ------------------------------- ? 0.3v to 550 v ? drain to source voltage, v ds, (RT8497c) -------------------------------- ------------------------------ 550 v ? drain to source voltage, v ds, (RT8497, RT8497a) -------------------------------- ------------------ ? 0.3v to 500v ? drain current, i d @ t c = 25 ? c -------------------------------- -------------------------------- ---------------- 1.4a ? drain current, i d @ t c = 100 ? c -------------------------------- -------------------------------- -------------- 0.9a ? power dissipation, p d @ t a = 25 ? c sop - 8 -------------------------------- -------------------------------- -------------------------------- ------------------- ? 0.53 w ? package thermal resistance (note 2) sop - 8 , ? ja -------------------------------- -------------------------------- -------------------------------- ------------- ? 188 ? c/w ? lead temperature (soldering, 10 sec.) -------------------------------- -------------------------------- --------- ? 260 ? c ? junction temperature -------------------------------- -------------------------------- ------------------------------- ? 150 ? c ? storage temperature range -------------------------------- -------------------------------- ---------------------- ?? 65 ? c to 150 ? c ? esd susceptibility (note 3 ) hbm (human body model) -------------------------------- -------------------------------- ------------------------ ? 2 kv mm (machine mode l ) -------------------------------- -------------------------------- -------------------------------- ? 2 0 0v recommended operating conditions (note 4) ? supply input voltage -------------------------------- -------------------------------- -------------------------------- ? 10 v to 30 v ? ambient temperature range -------------------------------- -------------------------------- ---------------------- ?? 40 ? c to 85 ? c ? junction temperature range -------------------------------- -------------------------------- --------------------- ?? 40 ? c to 125 ? c electrical characteristics ( v cc = 24v, t a = 25 ? c , unless otherwise specified ) parameter symbol test conditions min typ max unit vcc uvlo on v uvlo_on 17 18 19 v vcc uvlo off v uvlo_off 6.4 7.2 8 v vcc shut down current i s h d n v cc = 1 5 v -- -- 1 ? a vcc quiescent current i q drain stands still -- 0.5 5 ma vcc operating current i cc by c gate = 1nf, freq. = 20 kh z -- 1 5 ma vcc ovp level v ovp -- 34 -- v current sense threshold v sense 242.5 250 257.5 mv and pin leakage current i and v and = 5v -- 1 2 ? a static drain - source on - resistance r ds ( on ) v gs = 1 2 v , i d = 100ma RT8497 -- 5.2 -- ? RT8497a -- 2 -- RT8497b -- 4.2 -- RT8497c -- 7 --
rt84 9 7 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8497 - 01 july 2015 4 parameter symbol test conditions min typ max unit drain - source leakage current i dss RT8497 , v ds = 500v -- -- 10 ? a RT8497a , v ds = 500v RT8497b , v ds = 600v RT8497c , v ds = 600v note 1. stresses beyond those listed absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and 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 may affect device reliabili ty. note 2. ? ja is measured at t a = 25 ? c on a high effective thermal conductivity four - layer test board per jedec 51 - 7. note 3. devices are esd sensitive. handling precaution recommended. note 4. the device is not guaranteed to function outside its operating conditions
rt84 9 7 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8497 - 01 july 2015 www.richtek.com 5 typical application circuit figure 1. typical application of buck type 3 2 1 8 4 e c 1 l 1 b o o t s t r a p d i o d e r 2 d 1 r 1 o p t i o n a l c i n a n d v c c s o u r c e s g n d v c c 2 d r a i n 5 , 6 c 1 + d 2 b r i d g e r e c t i f i e r + - r t 8 4 9 7 r 3 ( o p t i o n a l )
rt84 9 7 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8497 - 01 july 2015 6 typical operating characteristics operating current vs. supply voltage 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0 10 20 30 40 supply voltage (v) operating current (ma) gate with 1nf operating current vs. temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -50 0 50 100 150 temperature (c) operating current (ma) v cc = 24v, gate with 1nf ovp vs. temperature 30 31 32 33 34 35 36 37 38 39 40 -50 -30 -10 10 30 50 70 90 110 130 150 temperature (c) ovp (v) uvlo vs. temperature 0 2 4 6 8 10 12 14 16 18 20 -50 0 50 100 150 temperature (c) uvlo (v) uvlo_on uvlo_off sense threshold vs. supply voltage 0 50 100 150 200 250 300 350 400 450 500 0 10 20 30 40 supply voltage (v) sense threshold (mv) sense threshold vs. temperature 0 50 100 150 200 250 300 350 400 450 500 -50 0 50 100 150 temperature (c) sense threshold (mv) v cc = 24v
rt84 9 7 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8497 - 01 july 2015 www.richtek.com 7 efficiency vs. input voltage 75 80 85 90 95 100 85 105 125 145 165 185 205 225 245 265 input voltage (v) efficiency (%) v in_ac = 90v to 264v i out = 320ma, led 16pcs, l = 470h RT8497a output current vs. input voltage 270 280 290 300 310 320 330 340 350 360 370 85 105 125 145 165 185 205 225 245 265 input voltage (v) output current (ma) v in_ac = 90v to 264v i out = 320ma, led 16pcs, l = 470h RT8497a power factor vs. input voltage 0.70 0.75 0.80 0.85 0.90 0.95 1.00 85 105 125 145 165 185 205 225 245 265 input voltage (v) power factor v in_ac = 90v to 264v i out = 320ma, led 16pcs, l = 470h RT8497a v in_ac = 264v input and output current time (5ms/ div ) v in (500v/ div ) v out (50v/ div ) i in (200ma/ div ) i out (500ma/ div ) i out = 320ma , led 16pcs , l = 470h power on time (100ms/ div ) v in (500v/ div ) v out (20v/ div ) i out (200ma/ div ) v in_ac = 264v i out = 320ma , led 16pcs , l = 470h power off time (100ms/ div ) v in (500v/ div v out (20v/ div ) i out (200ma/ div ) v in_ac = 264v i out = 320ma , led 16pcs , l = 470h
RT8497 preliminary copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8497 - 01 july 2015 8 total harmonic distortion 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 class c measured v in_ac = 115v i out = 320ma, led 16pcs, l = 470h total harmonic distortion 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 class c measured v in_ac = 230v i out = 320ma, led 16pcs, l = 470h
preliminary RT8497 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8497 - 01 july 2015 www.richtek.com 9 application information RT8497 is a boundary mode convertor, which can be used in buck configuration, to provide a constant output current to the (led) load. it contains special circuitry for achieving high power factor and low input current thd, while minimizing external compone nt count. the RT8497 integrates a power mosfet and housed in a sop - 8 package. thus, the components in the whole led driver system can be made very compact . the RT8497 can achieve high accuracy led output current via the average current feedback loop control. the internal sense voltage (250mv typ.) is used to set the average output current. the average current is set by the external resistor, rs. the sense voltage is also used for over current protection (ocp) function. the typical ocp threshold is abo ut seven times of the sense voltage threshold. under voltage lockout (uvlo) the RT8497 includes a uvlo function with 10.8v hysteresis. for system start up, the vin must rise over 18v (typ.) to turn on the internal mosfet. the internal mosfet will turn off if vin falls below 7.2v (typ.) setting average output current the output current that flows through the led string is set by an external resistor, rs, which is connected between the gnd and source pins. the relationship between output current, i out , and r s is shown below : start - up resistor the start - up resistor should be chosen to set the start up current exceeds certain minimum value. otherwise, the RT8497 may latch off and the system will never start. the start - up current equals (for 110vac regions), and equals (for 220vac regions). the typical required minimum start - up current is 100 ? a. the typical total start up resistance (r1+ r2) is around 1m ohm for universal inputs. input diode bridge rectifier selection the current rating of the input bridge rectifier is dependent on the v out /v in conversion ratio and out led current. the voltage rating of the input bridge rectifier, v br , on the other hand, is only dependent on the input voltage. thus, the vbr rating is calculated as below : where v ac(max) is the maximum input voltage (rms) and the parameter 1.2 is used for safety margin. for this example : if the input source is universal, v br will reach 448v. in this case, a 600v, 0.5a bridge rectifier can be chosen. input capacitor selection for high power factor application, the input capacitor cin should use a small value capacitance to achieve line volt age sine - wave. the voltage rating of the input filter capacitor, v cin , should be large enough to handle the input voltage. v cin (1.2 2 v ac(max) ) = (1.2 2 264) = 448v thus, a 0.1 ? f / 500v film capacitor can be chosen in this case. inductor selection for high power factor application, the RT8497 operates the co nverter in bcm (boundary - condition mode). the inductance range is defined by peak current of inductor maximum and minimum value of switching on time and off time, for ensuring the induc tor operates in bcm. the peak current of inductor is showed as below : and the inductance range is showed as below : ? ? out s 250 i = ma r ? ? ? ? 2 90v / r1 +r2 ? ? ? ? ? 2 180v / r1 +r2 ? ? ? br ac(max) v = 1.2 2 v ?? ? ? ? ? br ac(max) v = 1.2 2 v = 1.2 2 264 = 448v ? ? ? ? ? ? peak peak 2pin i = v f a out peak v where a = v ? ? ? ? 4 3 2 f a -0.411a +0.296a -0.312a +0.638a-0.0000846 , a|0~0.7 ?
RT8497 preliminary copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8497 - 01 july 2015 10 where 0.5 ? s ? t on ? 35 ? s and 2 ? s ? t off ? 30 ? s the frequency at the top of the sine wave can be calculated : (t delay is determined by the resistor connected to and pin , see turn on delay time) turn on delay time after the inductor current has reached zero, a resonance will occur between the inductor and the mosfet drain - source capacitance. in order to minimize the mosfet switching losses, RT8497 provides the flexibility to adjust the delay time of next switch - on cycle in order to switch - on at the maximum point of the resonance, which corresponds to the minimum drain - source voltage value. the delay time from zero current point to the maximum of the switch resonance which can be calculated from : where c sw is the capacitance at the switch node, mostly determined by the mosfet drain - source capacitance. the delay time t delay from zero current detection point to next mosfet switch - on cycle can be adjusted by the resistor value r3b connected between and pin and ic gnd t delay ( s ) = ( - 0.4 x r3b 2 +3500 x r3b+407500 ) x 10 - 6 r3 b resister value in k ? . forward diode selection when the power switch turns off, the path for the current is through the diode connected between the switch output and ground. this forward biased diode must have minimum voltage drop and recovery time. the reverse voltage rating of the diode should be greater than the maximum input voltage and the current rating should be greater than the maximum loa d current. the peak voltage stress of diode is : the input source is universal (v in = 85v to 264v), v d will reach 448v. thermal protection (otp) a thermal protection feature is included to protect the RT8497 from excessive heat damage. when the junction temperature exceeds a threshold of 150c, the thermal protection otp will be triggered and the internal mosfet will be turned off. thermal consider ations 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 te mperature. 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. for recommended operating condition specifications, the maximum junction temperature is 125 ? c. the junction to ambient thermal resistance, ? ja , is layout dependent. for sop - 8 package, the thermal resistance, ? ja , is 188 ? 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) / (188 ? c/w) = 0.53w for sop - 8 package the maximum power dissipation depends on the operating ambient tempe rature for fixed t j(max) and thermal resistance, ? ja . the derating curve in figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. ? ? peak out on out off peak peak v v t vt l = = ii ? sw on off delay 1 f = t + t + t resonance sw t = l1 c ? ? ? ? ? ? d ac(max) v 1.2 2 v = 1.2 2 264 = 448v ? ? ? ? ?
preliminary RT8497 copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8497 - 01 july 2015 www.richtek.com 11 figure 2 . derating curve of maximum power dissipation layout cons iderations for best performance of the RT8497, the following layout guidelines should be strictly followed. the hold up capacitor, c 1, must be placed as close as possible to the vcc pin. the compensation capacitor, c2, and delay resistor, r3b, must be pla ced as close as possible to the vc and the and pin. the ic source pin are high frequency switching nodes. the traces must be as wide and short as possible. keep the main traces with switching current as short and wide as possible. place c in , l1, rs, c out , and d1 as close to each other as possible. figure 3 . pcb layout guide p l a c e t h e c a p a c i t o r c 1 a s c l o s e a s p o s s i b l e t o t h e v c c p i n v m a i n c i n p o w e r g n d l 1 l e d - l e d + r s c 1 c o u t d 1 a n a l o g g n d d 2 r b r 1 p l a c e t h e c o m p e n s a t i o n c o m p o n e n t s c 2 a n d r 3 b a s c l o s e a s p o s s i b l e t o t h e i c a n a l o g g n d r 2 c 2 r 3 b v c c n a r r o w t r a c e f r o m m a i n c i r c u i t t o t h e i c t o a v o i d t h e s w i t c h i n g n o i s e z d ( o p t i o n ) p l a c e t h e d i o d e d 1 a n d t h e r e s i s t o r r s a s c l o s e a s p o s s i b l e t o t h e s o u r c e p i n r t 8 4 9 7 1 2 3 4 5 6 7 8 g n d v c a n d s o u r c e d r a i n d r a i n n c v c c k e l v i n s e n s e f r o m t h e s e n s e r e s i s t o r d i r e c t l y f r o m t h e b o t t o m e n d o f t h e s e n s e r e s i s t o r i s n e c e s s a r y t o a v o i d t h e s e n s e t h r e s h o l d s e t t i n g e r r o r b y t h e p a r a s i t i c p c b t r a c e r e s i s t a n c e . 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 25 50 75 100 125 ambient temperature (c) maximum power dissipation (w) 1 four-layer pcb
RT8497 preliminary copyright ? 2015 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8497 - 01 july 2015 12 outline dimension symbol dimensions in millimeters dimensions in inches min max min max a 4.801 5.004 0.189 0.197 b 3.810 3.988 0.150 0.157 c 1.346 1.753 0.053 0.069 d 0.330 0.508 0.013 0.020 f 1.194 1.346 0.047 0.053 h 0.170 0.254 0.007 0.010 i 0.050 0.254 0.002 0.010 j 5.791 6.200 0.228 0.244 m 0.400 1.270 0.016 0.050 8 - lead sop plastic packag e richtek technology corporation 14f, no. 8, tai yuen 1 st street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 richtek products are sold by description only. richtek reserves the right to change the circuitry and/or specifications without notice at any time. customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is curre nt and complete. ric htek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a richtek product. information furnished by richtek is believed to be accurate and reliable. however, no responsibility is assumed by richtek or its subsid iaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of richtek or its su bsidiaries.

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