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RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8402 - 00 january 2017 www.richtek.com 1 phase - cut dimmable high side buck led driver with high power factor general description the RT8402 is a boundary mode controller that can provide good pfc and be suitable for wall dimmer. the RT8402 supports phase - cut dimmers, including leading - edge (triac) and trailing - edge dimmers. it is used for buck converter and can be compatible with triac dimmer. the external mosfet is switched by internal gate driver and the feedback circuit regulates output c urrent precisely. the RT8402 features a zcs detector which keeps system operating in bcm and obtaining excellent power efficiency, better emi performance. the robust dimming control method can adjust the output current following the triac turn on angle and avoid abnormal flicker. t his driver can use a cheap simple drum core inductor in the system instead of an ee core to obtain high efficiency. the RT8402 is housed in a tsot - 23 - 6 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. ? suitable for use in snpb or pb - free soldering processes features ? built - in power mosfet ? active power factor correlation ? programmable constant led current with high - precision current regulation ? excellent line and load regulation ? suit for high side buck low bom cost requirement ? unique dimming control method to be compatible with tr iac dimmer ? used in low input voltage range ? support low percentage dimming angle ? built - in over thermal protection ? output led string open protection ? output led string short protection ? over current protection applications ? e27, par, light bar, offline led lig hts pin configuration (top view) tsot - 23 - 6 marking information r t 8 4 0 2 p a c k a g e t y p e j 6 : t s o t - 2 3 - 6 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 ) v c c s g n d g a t e d i m v c s e n s e 4 2 3 5 6 2 q = d n n 2 q = : p r o d u c t c o d e d n n : d a t e c o d e
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8402 - 00 january 2017 2 simplified application circuit functional pin description pin no. pin name pin function 1 vcc supply voltage input of the chip . for good bypass, a ceramic capacitor near the vcc pin is required. 2 sgnd ground of the chip. 3 gate gate driver for external mosfet . 4 sense led current sense input. 5 vc close loop compensation node. 6 dim internal dimming function. r t 8 4 0 2 l 1 b o o t s t r a p d i o d e d 2 r 4 d 1 q 1 r 2 a c 1 r 1 r 2 b d i m v c c s e n s e g a t e s g n d v c c 3 r g c 2 r 3 z d 1 b r i d g e r e c t i f i e r c i n l i n e n e u t r l e c 1 +
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8402 - 00 january 2017 www.richtek.com 3 functional block diagram operation the RT8402 senses the average output current and regulates the current precisely. the vc pin is the stability compensation node in this close loop. to stabilize the system and achieve better pfc / thdi, proper selection of a compensation network is needed. by using boundary mode control, it provides good efficiency performance. the dimming characteristic can be optimized by adjusting the external setting of dim pin. g a t e r e g u l a t o r s g n d d i m 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 e n s e d u t y d e t e c t i o n
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8402 - 00 january 2017 4 absolute maximum ratings (note 1) ? vcc supply voltage, vcc -------------------------------- -------------------------------- ---------------------- 40v ? vc, dim, sense to sgnd voltage -------------------------------- -------------------------------- ----------- ? 0.3v to 6v ? power dissipation, p d @ t a = 25 ? c tsot - 23 - 6 -------------------------------- -------------------------------- -------------------------------- ------------ ? 0. 44 w ? package thermal resistance (note 2) tsot - 23 - 6 , ? ja -------------------------------- -------------------------------- -------------------------------- ------ ? 226.5 ? c/w tsot - 23 - 6 , ? jc -------------------------------- -------------------------------- -------------------------------- ------ ? 18.9 ? 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 recommended operating conditions (note 4) ? vcc supply 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_o ff 6 6.8 7.6 v vcc shutdown current i sd v cc = v uvlo_o n ? 3v -- -- 2 ? a vcc operating current i cc by cgate = 1nf, v cc =24v v c =1v, sense = 0v 1.1 1.8 2.5 ma vcc 30v operating current i cc by cgate = 1nf, v cc = 30v v c =1v, sense = 0v 2 2.7 3.4 ma vcc ovp level v ovp 34.5 37 39.5 v vcc clamp level v cc_clamp -- 29 -- v vcc clamp current i cc_c lamp -- 0.85 -- ma sense pin leakage current i sense v sense = 3v -- -- 2 ? a current sense threshold v sense 240 250 260 mv dim pin leakage current i dim v dim = 5v -- -- 1 ? a gate voltage high v gate_h i gate = 0ma 10 12.5 15 v i gate = 10ma 9 12 15
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8402 - 00 january 2017 www.richtek.com 5 parameter symbol test conditions min typ max unit gate driver rising time t r c l = 1nf -- 80 -- ns falling time t f c l = 1nf -- 50 -- 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 reliability. note 2. ? ja is measured under natural convection (still air) at t a = 25 ? c with the component mounted on a low effective - thermal - conductivity two - layer test board on a jedec thermal measurement standard. ? jc is measured at the exposed pad of the package. note 3. devices are e sd sensitive. handling precaution recommended. note 4. the device is not guaranteed to function outside its operating conditions
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8402 - 00 january 2017 6 typical application circuit figure 1. typical application of buck type r t 8 4 0 2 6 5 2 1 4 3 e c 1 l 1 b o o t s t r a p d i o d e d 2 r 4 d 1 q 1 r 2 a c 1 r 1 b r i d g e r e c t i f i e r r 2 b d i m v c c s e n s e g a t e s g n d v c c 3 r g c 2 + z d 2 ( o p t i o n ) r 3 z d 1 + e c 2 r 5 l i n e n e u t r l r 6 c i n
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8402 - 00 january 2017 www.richtek.com 7 typical operating characteristics quiescent 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 5 10 15 20 25 30 35 40 supply voltage (v) quiescent current (ma) v c = 0v quiescent 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 -25 0 25 50 75 100 125 temperature (c) quiescent current (ma) v c = 0v, v cc = 24v operating current vs. supply voltage 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 0 5 10 15 20 25 30 35 40 supply voltage (v) operating current (ma) gate with 1nf, v c = 2v, sense = 0v 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 -25 0 25 50 75 100 125 temperature (c) operating current (ma) gate with 1nf, v c = 2v, sense = 0v, v cc = 24v vcc clamp current vs. temperature 0.70 0.75 0.80 0.85 0.90 0.95 1.00 -50 -25 0 25 50 75 100 125 temperature (c) vcc clamp currrent ( ma) ovp vs. temperature 30 31 32 33 34 35 36 37 38 39 40 -50 -25 0 25 50 75 100 125 temperature (c) vcc ovp ( v)
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8402 - 00 january 2017 8 uvlo vs. temperature 0 2 4 6 8 10 12 14 16 18 20 -50 -25 0 25 50 75 100 125 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 5 10 15 20 25 30 35 40 supply voltage (v) sense threshold (mv) sense threshold vs. temperature 0 50 100 150 200 250 300 350 400 450 500 -50 -25 0 25 50 75 100 125 temperature (c) sense threshold (mv)
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8402 - 00 january 2017 www.richtek.com 9 application information the RT8402 is a boundary mode, high efficiency constant current controller with internal high side driver, 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 f actor and low input current thd, while minimizing external component count. the small sot23 - 6 package keeps application footprint small, and makes the RT8402 a cost effective solution for off - line led drivers. the RT8402 can achieve high accuracy led outpu t 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 about seven times of the sense voltage threshold. under voltage lockout (uvlo) the RT8402 includes a uvlo function with 11.2v hysteresis. for system start up, the vin must rise over 18v (typ.) to turn on the i nternal mosfet. the internal mosfet will turn off if vin falls below 6.8v (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 sgnd and sense pins. the relationship between output current, iout, and rs 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 RT8402 may latch off and the system will never start. the start - up current equals (for 110vac regions), and equals (for 220vac regions). the typica l required minimum start - up current is 100 ? a. the typical t otal start up resistance (r1 ) 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, vbr, 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 voltage 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 RT8402 operates the converter 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 inductor 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 ? ? ? 2 180v / r1 ? ? ? 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 ?
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8402 - 00 january 2017 10 where 0.5 ? s ? t on ? 35 ? s ( typ. ) and 5 ? s ? t off ? 35 ? s ( typ. ) . the frequency at the top of the sine wave can be calculated : t delay is about 0.6 ? s ( typ. ) . 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 gre ater than the maximum input voltage and the current rating should be greater than the maximum load current. the peak voltage stress of diode is : the input source is universal (v in = 85v to 264v), v d will reach 448v. mosfet selection the peak current through this mosfet will be over the maximum output current. this component current rating should be greater than 1.2 times the maximum load current and the reverse voltage rating of the mosfet should be greater than 1.2 times the maximum input voltage, assuming a 20% output current ripple. the peak voltage rating of the mosfet is : the largest peak current will occur at the highest vin. the current rating of mosfet is determined by the ocp threshold which is about seven times of the sense voltage threshold. thermal protection (otp) a thermal protection feature is included to protect the RT8402 from excessive heat damage. when the junction temperature exceeds a threshold of 150 c (typ.), the thermal protection otp will be triggered and the internal mosfet will be turned off. thermal protection (otp) a thermal protection feature is included to protect the rt 8402 from excessive heat damage. when the junction temperature exceeds a threshold of 150c (typ.), the thermal protection otp will be triggered and the internal mosfet will be turned off. thermal considerations the junction temperature should never exceed the absolute maximum junction temperature t j(max) , listed under absolute maximum rat ings, to avoid permanent damage to the device. the maximum allowable power dissipation depends on the thermal resistance of the ic package, the pcb layout, the rate of surrounding airflow, and the difference between the junction and ambient temperatures. t he maximum power dissipation can be calculated using 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 continu ous operation, the maximum operating junction temperature indicated under recommended operating conditions is 125 ? c. the junction - to - ambient thermal resistance, ?? ja , is highly package dependent. for a tsot - 23 - 6 package, the thermal resistance, ? ja , is 226.5 ? c/w on a standard jedec low effective - thermal - conductivity two - layer test board. the maximum power dissipation at t a = 25 ? c can be calculated as below : p d(max) = (125 ? c ? 25 ? c) / ( 226.5 ? c/w) = 0. 44 w for a tsot - 23 - 6 package. the maximum power dissipation depends on the operating ambient temperature for the fixed t j(max) and the thermal resistance, ? ja . the derating curves 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 ? ? ? ? d ac(max) v 1.2 2 v = 1.2 2 264 = 448v ? ? ? ? ? q1 ac(max) v = 1.2 ( 2 v ) = 1.2 ( 2 264) = 448v ? ? ? ?
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8402 - 00 january 2017 www.richtek.com 11 figure 2 . derating curve of maximum power dissipation layout considerations for best performan ce of the RT8402, the following layout guidelines should be strictly followed. the hold up capacitor, c1, must be placed as close as possible to the vcc pin. the comp ensation capacitor, c2, and c3 , must be placed as close as possible to the dim and the vc pin. the ic gate and gnd pin are high frequency switching nodes. both 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, q1, r 4 , ec1 , 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 4 q 1 c 1 r g e c 1 d 1 a n a l o g g n d 1 v c c v c s g n d d i m s e n s e g a t e 5 2 3 6 4 r 3 r 1 r t 8 4 0 2 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 c 3 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 c 3 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 s e n s e z d 1 p l a c e t h e m o s f e t q 1 , 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 4 a s c l o s e a s p o s s i b l e t o t h e e a c h o t h e r 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 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 . + r 2 a r 2 b c 2 e c 2 + z d 2 ( o p t i o n ) b o o t s t r a p d i o d e d 2 r 5 r 6 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 two-layer pcb
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. www.richtek.com ds8402 - 00 january 2017 12 outline dimension symbol dimensions in millimeters dimensions in inches min max min max a 0.700 1.000 0.028 0.039 a1 0.000 0.100 0.000 0.004 b 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 c 2.591 3.000 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024 tsot - 23 - 6 surface mount package
RT8402 copyright ? 2017 richtek technology corporation. all rights reserved. is a registered trademark of richtek technology corporation. ds8402 - 00 january 2017 www.richtek.com 13 footprint information package number of pin footprint dimension (mm) tolerance p1 a b c d m tsot - 26/tsot - 26(fc)/sot - 26 6 0.95 3.60 1.60 1.00 0.70 2.60 0.10 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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