ac/dc current mode pwm power management controller absolute maxim ratings item symbol typical unit power supply vdd 9 12 v fb start voltage vs 5 v fb under-voltage threshold vu 3.5 v fb clamp voltage vo 5.5 v fb input current i fb <1 ma switching frequency fs 65 khz maximum duty cycle d max 75 fb sw current gain g f 0.3 a/v current limit i lim 400 ma sw break down voltage vsw >400 v stand by current p s <0.3w w system efficiency (full load) >70 % ? 65khz switching frequency ? emitter drive of internal power transistor ? over-current protection, over and under-voltage protection ? current mode pwm ? low power for green environments protection, as lower as 0.3w ? lowest total cost solution z etc. z offline power generator z power adapter the LR2257 ac?dc is a high efficiency current-mode pwm power supply controller that drives an internal npn transistor for high voltage switching. apply with bicmos technology, the device consist of bandgap reference voltage, oscillator, high voltage switching transistor and build in safety features of over current and over voltage protection mechanisms delivering up to 3w yet consumes, the typical application of the device will include: z battery charger, such as handset phone LR2257 1/8 leshan radio company, ltd.
pin name 1 2/9 leshan radio company, ltd. LR2257
working principle block diagram sw s gnd driver + - reference voltage r r2 fb q r3 r1 t2 oscillator + + - protection t1 gate vdd circuit starter 1 2 pc817a lo - hi 1n5817 1 2 hi 10uf 10v 2% t=114 100uf 10v hv dc 22uf 35v 3 fb d6 5.1v 1 2 + 5 lo 1m ic2 1 2 vdd gnd 6.2v dc 7 1n4148 6 sw t=24 8 1n4148 t=8 1 2 LR2257 4 3/8 leshan radio company, ltd. LR2257
electrical characteristics test condition t a =25c,v fb 4v parameter symbol test condition min typ max unit power supply v dd 8.5 12 v fb start voltage vs 5 v fb under-voltage threshold vu 3.25 3.5 3.65 fb clamp voltage vo 10ma 5.2 5.5 5.8 v fb input current i fb - - 0.7 1 ma switching frequency fs - - 70 - khz maximum duty cycle d max v fb =4v, i sw =10ma 70 75 80 % minimum duty cycle d min v fb =4.6v, i sw =100ma 3.5 5.5 % current limit i lim v fb =v uv +0.1v - 400 - ma fb to sw current gain g fb - -0.29 - a/v fb dynamic impedance r fb /v fb - 9 - k sw break down voltage vsw >400 v stand by power p s <0.3 w system efficiency (full load) 74 % 4/8 leshan radio company, ltd. LR2257
application c13 r8d 6. 2 220 r6 800m a r7 l2 c10 10nf d c + 1 1n4007 d5 8 85-265v ac t=8 330uf/10v 7 2 tl431 d10 hi 2.5m h l1 l3 1k r18 c4 f1 1uf c11 4 220 r9 10nf c6 1k r1 5.6k r14 rt1 15 3 pc817a 1n4148 ac1 fr107 d6 c5 hi 65u 200k r16 r5 100k 10k r12 6 6u -+ 4700pf/1kv 220 10uf/50v 1m r3 hi d c - 4.7uf/400v c2 500pf c7 5.1k r13 t=24 r8a 6. 2 c3 10uf/50v r10 390 ic2 c5 680uf/10v d7 4.7uf/400v c1 ac2 1n5817 100 r5a 5 q1 t=114 hi 510 r4 LR2257 5/8 leshan radio company, ltd. LR2257
characteristics curve (vac= 110v) 0% 10% 20% 30% 40% 50% 60% 70% 80% 0123456 w ? cv cc (vac =220v) 0% 10% 20% 30% 40% 50% 60% 70% 80% 0123456 ?w ? cc cv po (w) (%) vs po (vac=220v) po (w) (%) vs po (vac=110v) 6/8 leshan radio company, ltd. LR2257
en55022a 150khz 30mhz 10mhz 1mhz 20 10 30 40 50 70 60 80 dbuv emi recommended pcb layout 7/8 leshan radio company, ltd. LR2257
so-8 dimension *typical inch mm inch mm dim min. max. min. max. dim min. max. min. max. a 0.1909 0.2007 4.85 5.10 i 0.0019 0.0078 0.05 0.20 b 0.1515 0.1555 3.85 3.95 j 0.0118 0.0275 0.30 0.70 c 0.2283 0.2441 5.80 6.20 k 0.0074 0.0098 0.19 0.25 d 0.0480 0.0519 1.22 1.32 l 0.0145 0.0204 0.37 0.52 e 0.0145 0.0185 0.37 0.47 m 0.0118 0.0197 0.30 0.50 f 0.1472 0.1527 3.74 3.88 n 0.0031 0.0051 0.08 0.13 g 0.0570 0.0649 1.45 1.65 o 0.0000 0.0059 0.00 0.15 h 0.1889 0.2007 4.80 5.10 top view a b front view f c d e g i h j k l part a o m right side view part a n 1 2 3 4 d2257 8 7 6 5 8/8 leshan radio company, ltd. LR2257
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