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an-087e rev.1.0 april-2011 1 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ fuji switching power control ic FA5526/5527/5528 fa5536/5537/5538 application note april.-2011 fuji electric co., ltd. http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 2 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ 1. this data book contains the product specifications, characteristics, data, materials and structures as of april in 2011. the contents are subject to change without prior notice for specification changes or other reasons. when using a product listed in this data book, be sure to obtain the latest specifications and check the data. 2. all applications described in this data book give examples of applications of fuji electric?s products for your reference. no right or license, either express or implied, under any patent, copyright, trade secret or other intellectual property right owned by fuji electric co., ltd. shall be granted. 3. although fuji electric co., ltd. continually strives to enhance product quality and reliability, a small percentage of semiconductor products may become faulty. when using fuji electric semiconductor products in your equipment, be sure to take adequate safety measures such as redundant, flame-retardant and fail-safe design in order to prevent a semiconductor product failure from leading to a physical injury, property damage or other problems. 4. the products introduced in this data book are intended for use in the following electronic and electrical equipment which requires ordinary reliability: ? computers ? oa equipment ? communications equipment (terminal devices) ? measurement equipment ? machine tools ? audiovisual equipment ? electrical home appliances ? personal equipment ? industrial robots, etc. 5. if you need to use a semiconductor product in this data book for equipment requiring higher reliability than normal, such as listed below, be sure to contact fuji electric device technology co., ltd. to obtain prior approval. when using these products, take adequate safety measures such as a backup system to prevent the equipment from malfunctioning when a fuji electric?s product incorporated in the equipment becomes faulty. ? transportation equipment (mounted on vehicles and ships) ? trunk communications equipment ? traffic-signal control equipment ? gas leakage detectors with an auto-shutoff function ? disaster prevention / security equipment ? safety devices 6. do not use a product in this data book for equipment requiring extremely high reliability such as: ? space equipment ? airborne equipment ? atomic control equipment ? submarine repeater equipment ? medical equipment 7. all rights reserved. no part of this data book may be reproduced without permission in writing from fuji electric co., ltd. 8. if you have any question about any portion of this data book, ask fuji electric co., ltd. or its sales agencies. neither fuji electric co., ltd. nor its agencies shall be liable for any injury or damage caused by any use of the products not in accordance with instructions set forth herein. warning http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 3 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ contents 1 outline ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 4 2 features ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 4 3 external dimension diagram ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 4 4 block diagram ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 5 5 pin assignments ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 5 6 selection guide of FA5526/27/28/36/37/38 series ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 6 7 ratings and characteristics ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 6 to 9 8 characteristic curves ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 10 to 14 9 description of block circuits ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 15 to 24 10 design advice ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 25 to 32 11 examples of application circuits ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 33 note ? the contents of this data book are subject to change without prior notice for improvement or other reasons. ? application examples and parts constants listed in this data book are intended for design reference, without giving due consideration to unevenness in parts characteristics and usage conditions. when using, be sure to design the relevant circuit giving due consideration to unevenness in parts characteristics and usage conditions. http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 4 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ 1. outline FA5526/27/28/36/37/38 series are current-mode switching power control ics that can directly drive power mosfets. low-power dissipation is achieved due to adoption of high break-down voltage cmos process. in addition, stand-by power consumption can substantially be reduced due to a built-in start-up circuit. many functions are incorporated in an eight pin package, reducing the number of external parts and allowing compact and high cost performance power supply 2. features ? b u i l t - i n s t a r t - u p c i r c u i t o f 5 0 0 v b r e a k - d o w n v o l t a g e t h a t i s c u t o f f a f t e r s t a r t - u p ( i n p u t c u r r e n t a f t e r c u t o f f : 2 5 a ( t y p . ) ) ? l o w p o w e r d i s s i p a t i o n d u e t o a d o p t i o n o f h i g h b r e a k - d o w n v o l t a g e c m o s p r o c e s s supply current in operating mode : 1.4ma (typ.) ( for fa5528 and fa5538 ) ? b u i l t - i n f r e q u e n c y - d e c r e a s i n g f u n c t i o n a t l i g h t l o a d ? o s c i l l a t i n g f r e q u e n c y FA5526/5536 : 130khz(typ.), fa5527/5537 : 100khz(typ.), fa5528/5538 : 60khz(typ.) ? b u i l t - i n l a t c h - m o d e c u t o f f f u n c t i o n o f o v e r l o a d ( o v e r c u r r e n t ) f o r f a 5 5 2 6 / 5 5 2 7 / 5 5 2 8 ? b u i l t - i n a u t o - r e c o v e r y c u t o f f f u n c t i o n o f o v e r l o a d ( o v e r c u r r e n t ) f o r f a 5 5 3 6 / 5 5 3 7 / 5 5 3 8 ? b u i l t - i n l a t c h - m o d e c u t o f f f u n c t i o n o f o v e r - v o l t a g e f o r 2 8 v ( t y p . ) a t v c c p i n f o r f a 5 5 2 6 / 5 5 2 7 / 5 5 2 8 . ? b u i l t - i n a u t o - r e c o v e r y - m o d e c u t o f f f u n c t i o n o f o v e r - v o l t a g e f o r 2 8 v ( t y p . ) a t v c c p i n f o r f a 5 5 3 6 / 5 5 3 7 / 5 5 3 8 . ? b u i l t - i n u n d e r v o l t a g e l o c k - o u t f o r v c c p i n ( 1 5 v : o n , 9 v : o f f ) ? 8 p i n s p a c k a g e ( d i p / s o ) 3. external dimension diagram unit mm so-8 FA5526n/27n/28n/36n/37n/38n dip-8 FA5526p/27p/28p/36p/37p/38p 0.400.1 0 - 8 1.27 0 . 6 5 0 . 2 5 0 . 2 0 4.90.1 0 . 1 8 0 . 0 8 6 . 0 0 . 2 1 . 7 m a x 3 . 9 0 . 1 1 4 58 4 6 . 5 5 0 . 2 5 + 0 . 1 / - 0 . 0 5 7.6 1.50.3 8 1 1.00.3 0.50.1 4 . 5 m a x 3 m i n 3 . 4 0 - 1 5 2.54 9.4 2.543=7.62 http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 5 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ 4. block diagram FA5526 / fa5527 / fa5528 for timer latched ocp fa5536 / fa5537 / fa5538 for auto-recovery ocp 5. pin assignments pin symbol function description 1 cs soft start/latch-mode stop time setting of soft start and over current protection 2 fb feedback input input for controlling current comparator threshold voltage 3 is current sensor input input for monitoring mosfet current 4 gnd ground power supply ground 5 out output output for directly driving a mosfet 6 vcc power supply power supply for ics 7 (nc) no connection no connection 8 vh high voltage input input terminal for start-up circuit 11a/4a 1.3ma 8.5v/7.9v latch 5v enb vcc uvlo 4.0v/3.5v start off 5v reg gnd (4) vcc (6) vh (8) cs (1) ovp uvlo 28v 2.9v overload 4.8v 15v/9v 20k 60k 7.4k 3r r fb (2) is (3) trg clr 1 shot q blanking out (5) out put enb q q s r f.f. is comp. 0.52v 1meg 5pf x1 buf 30v vco q t osc 0.28v slope generator - + 0.68v 11a/4a 1.3ma 8.5v/7.9v auto-recovery 5v enb vcc uvlo 4.0v/3.5v start off 5v reg gnd (4) vcc (6) vh (8) cs (1) ovp uvlo 28v 2.9v overload 4.8v 15v/9v 20k 60k 7.4k 3r r fb (2) is (3) trg clr 1 shot q blanking out (5) out put enb q q s r f.f. is comp. 0.52v 1meg 5pf x1 buf 30v vco q t osc 0.28v slope generator - + 0.68v http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 6 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ 6. line-up of FA5526/27/28/36/37/38 series type switching frequency (khz) over current protection package FA5526p/n 130 (typ.) latch with adjustable delay time dip-8/so-8 fa5527p/n 100 (typ.) latch with adjustable delay time dip-8/so-8 fa5528p/n 60 (typ.) latch with adjustable delay time dip-8/so-8 fa5536p/n 130 (typ.) auto-recovery dip-8/so-8 fa5537p/n 100 (typ.) auto-recovery dip-8/so-8 fa5538p/n 60 (typ.) auto-recovery dip-8/so-8 7. ratings and characteristics in defining a current, ? ? represents a sink current and ? ? a source current. (1) absolute maximum ratings item symbol rating unit low impedance source (icc>15ma) v cc1 28 v supply voltage built-in zener clamp (icc<15ma) v cc2 self limiting v i oh -0.3 a out pin peak current i ol +0.6 a out pin voltage v out -0.3 to vcc+0.3 v fb/ is pin voltage v lt -0.3 to 5.0 v cs pin sink current i cs 2.0 ma cs pin minimum voltage v csl -0.3 v vh pin voltage v vh -0.3 to 500 v total power dissipation (ta=25 ) pd 800 (dip-8) 400 (so-8) mw ambient temperature ta -30 to +85 degree maximum junction temperature tj 125 degree storage temperature tstg -40 to +150 degree permissible power dissipation decreasing characteristics -30 25 85 125 400mw(so) 800mw(dip) 0 ambie nt temperature ta ( ?? ) p e r m i s s i b l e p o w e r d i s s i p a t i o n http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 7 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (2) recommended operating conditions item symbol min typ max unit supply voltage v cc 10 18 26 v dc voltage v vh(dc) 80 450 v (dc) vh pin voltage ac line voltage v vh(ac) 80 288 v (ac) vh pin series resistor r vh 2.2 47 k ohm cs pin capacitor c cs 0.01 1 f vcc pin capacitor c vcc 10 33 f (3) electrical characteristics (vcc=18v, tj=25 , unless otherwise specified) oscillator (fb pin) item symbol condition min typ max unit FA5526/36 117 130 143 fa5527/37 90 100 110 oscillating frequency fosc fb=3v fa5528/38 54 60 66 khz supply voltage stability fdv vcc = 10 to 26v -2 2 % temperature stability fdt ta = -30 to 85 ?? +0.025 %/ ?? fb pin voltage for starting frequency variation vfbm 0.95 1.05 1.15 v FA5526/36 310 fa5527/37 240 frequency reduction ratio kf ?? f/ ?? vfb at fb pin =0.8v to 0.9v fa5528/38 140 khz/v FA5526/36 1.1 fa5527/37 1.1 oscillating frequency at light load f06 fb pin =0.6v fa5528/38 1.1 khz minimum frequency *1 fmin 0.4 1.1 3.0 khz *1 the frequency become much smaller than 1.1khz when intermittent switching occurs at light load near no load. pulse width modulator (fb pin) item symbol condition min typ max unit maximum duty cycle d max fb pin = 3v, cs pin = 3v 76 80 84 % minimum duty cycle d min fb pin = 0v, cs pin = 3v 0 % fb voltage for pulse stop v thfb0 duty cycle = 0% 200 280 360 mv fb pin current i fb0 fb pin = 0v -620 -520 -420 ua http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 8 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ current sensor (is pin) item symbol condition min typ max unit voltage gain av is ?? vfb/ ?? vis 3.8 4.0 4.2 v/v maximum threshold voltage vth is1 fb pin = 4v, duty = 10% 470 520 570 mv FA5526/36 -24 fa5527/37 -17 slope compensation value slp fb pin=4v fa5528/38 -12 mv/us FA5526/36 0.3 fa5527/37 0.5 minimum on pulse width tmin fb pin=3v cs pin=0v is pin=1v fa5528/38 0.7 us FA5526/36 0.2 fa5527/37 0.4 blanking time tblank fa5528/38 0.6 us output delay time tpd is is pin to out pin 100 ns soft-start circuit (cs pin) item symbol condition min typ max unit charging current i cs0 cs pin = 0v -15 -11 -5 u a threshold voltage for changing charging current v thcs1 ics = -12 ? ? -4 a 3 v input threshold voltage v thcs0 out pin width = tmin, fb pin = 3v 0.68 v over current protection circuit (cs pin) : latch off for FA5526/27/28 and auto-recovery for fa5536/37/38 item symbol condition min typ max unit charging current i cs4 cs pin = 4v -6 -4 -2 ua sink current i sink cs pin = 6v 34 59 84 ua v thcsf on ? off 8.0 8.5 9.0 v cutoff threshold voltage v thcsn off ? on 7.4 7.9 8.4 v hysteresis width v thhys v thcsf - v thcsn 0.6 v clamp voltage at latch mode v cs2 fb pin : open 8.9 v cutoff circuit at overload (fb pin) item symbol condition min typ max unit detection threshold voltage v thfb 3.3 3.6 3.9 v cutoff circuit at overvoltage (vcc pin) item symbol condition min typ max unit threshold voltage v thvcc 26 28 30 v cs pin charging current i socs2 cs pin = 4v -1.3 ma http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 9 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ malfunction-protective circuit at low voltage (vcc pin) item symbol condition min typ max unit on threshold voltage v ccon 13.2 15.0 16.8 v off threshold voltage v ccoff 8.0 9.0 10.0 v hysteresis width v hys v ccon - v ccoff 4.5 6.0 7.5 v output section (out pin) item symbol condition min typ max unit low output voltage v ol i ol = 100ma 0.5 1.0 v high output voltage v oh i oh = -100ma, v cc = 18v 14.8 16.4 v rise time tr c(load) = 1nf 37 ns fall time tf c(load) = 1nf 59 ns high voltage input section (vh pin, vcc pin) item symbol condition min typ max unit ihrun vh pin = 450v, vcc> vccon 12 25 37 ua vh pin input current ihstb vh pin = 100v, vcc = 0v 7.0 ma vcc voltage in latch mode v ccl vh pin = 100v 23 v ipre1 vcc = 10v, vh pin = 100v at start-up or protection mode ( ocp, ovp ) -6.6 -4.0 ma vcc pin charging current ipre2 vcc = 13v, vh pin = 100v at start-up or protection mode ( ocp, ovp ) -6.5 -3.5 ma consumption current (vcc pin) item symbol condition min typ max unit FA5526/36 1.6 2.4 fa5527/37 1.5 2.2 i ccop1 duty cycle = d max , fb pin =3v, no load fa5528/38 1.4 2.0 ma supply current during operation i ccop2 duty cycle = 0 , fb pin = 0v 1.6 2.4 ma consumption current in latch mode i ccl fb pin, cs pin : open 290 400 ua zener voltage vz iz = 2ma 30 v http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 10 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ 8. characteristic curves ? unless otherwise specified, ta=25 , vcc=18v ? in defining a current, ?+? represents a sink current and ?-? a source current. ? the data stated in this chapter are intended for giving typical ic characteristics and not for guaranteeing performance. variation ratio of switching frequency (delta fosc) vs. vcc pin voltage (vcc) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 10 15 20 25 30 vcc (v) d e l t a f o s c ( % ) switching frequency (fosc) vs. fb pin voltage 0 20 40 60 80 100 120 140 0 0.5 1 1.5 2 2.5 3 vfb (v) f o s c ( k h z ) FA5526 / 36 fa5527 / 37 fa5528 / 38 maximum duty cycle (dmax) vs. junction temperature (tj) 79.0 79.5 80.0 80.5 81.0 -40 -20 0 20 40 60 80 100 120 140 tj ?i degree ?j d m a x ( % ) variation ratio of switching frequency (delta fosc) vs. junction temperature (tj) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -40 -20 0 20 40 60 80 100 120 140 tj (degree) d e l t a f o s c ( % ) minimum switching frequency (fmin) vs. junction temperature (tj) 0.0 0.5 1.0 1.5 2.0 -40 -20 0 20 40 60 80 100 120 140 tj ?i degree ?j f m i n ( k h z ) minimum on width (tmin) vs. junction temperature (tj) 200 300 400 500 600 700 800 -40 -20 0 20 40 60 80 100 120 140 tj ?i degree ?j t m i n ( n s ) fa5528 / 38 fa5527 / 37 FA5526 / 36 http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 11 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ cs pin source current (ics) vs. junction temperature (tj) -14 -13 -12 -11 -10 -9 -40 -20 0 20 40 60 80 100 120 140 tj ?i degree ?j i c s ( u a ) cs=0v cs pin current (ics) vs. cs pin voltage (vcs) -20 -10 0 10 20 30 40 50 60 70 80 0 2 4 6 8 10 12 vcs (v) i c s ( u a ) fb=open uvlo on threshold voltage (vccon) vs. junction temperature (tj) 14.0 14.2 14.4 14.6 14.8 15.0 15.2 15.4 15.6 15.8 16.0 -40 -20 0 20 40 60 80 100 120 140 tj (degree) v c c o n ( v ) cs pin source current (ics) vs. junction temperature (tj) -6 -5.5 -5 -4.5 -4 -3.5 -40 -20 0 20 40 60 80 100 120 140 tj degree) i c s ( u a ) cs=4v cs pin current (ics) vs. cs pin voltage (vcs) -20 -10 0 10 20 30 40 50 60 70 80 0 2 4 6 8 10 12 vcs (v) i c s ( u a ) fb=3v uvlo off threshold voltage (vccoff) vs. junction temperature (tj) 8.0 8.2 8.4 8.6 8.8 9.0 9.2 9.4 9.6 9.8 10.0 -40 -20 0 20 40 60 80 100 120 140 tj (degree) v c c o f f ( v ) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 12 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ out pin high output voltage (voh) vs. vcc pin voltage (vcc) 1 1.5 2 2.5 3 10 15 20 25 30 vcc (v) v c c - v o h ( v ) ioh = -100ma is pin maximum input threshold volatge(vthis1) vs. junction temerature (tj) 0.47 0.48 0.49 0.50 0.51 0.52 0.53 -40 -20 0 20 40 60 80 100 120 140 tj (degree) v t h i s 1 ( v ) fb pin source current (ifb) vs. fb pin voltage (vfb) -600 -500 -400 -300 -200 -100 0 0 1 2 3 4 5 vfb (v) i f b ( u a ) out pin low output voltage (vol) vs. vcc pin voltage (vcc) 0.3 0.4 0.5 0.6 0.7 0.8 10 15 20 25 30 vcc (v) v o l ( v ) iol = 100ma is pin input threshold voltage (vthis) vs. fb pin voltage (vfb) 0 0.1 0.2 0.3 0.4 0.5 0.6 0 1 2 3 4 vfb (v) v t h i s ( v ) duty cycle = 50% threshold voltage of over-voltage protection (vthvcc) vs. junction temperature (tj) 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 -40 -20 0 20 40 60 80 100 120 140 tj (degree) v t h v c c ( v ) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 13 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ start-up circuit vcc pin source current (ipre) vs. vcc pin voltage (vcc) -8.0 -7.5 -7.0 -6.5 -6.0 -5.5 -5.0 0 5 10 15 vcc (v) i p r e ( m a ) vvh = 100v start-up circuit vcc pin source current vs. vh pin voltage (vvh) -7.4 -7.2 -7 -6.8 -6.6 -6.4 -6.2 -6 0 100 200 300 400 500 vvh (v) i p r e ( m a ) vcc = 0v is pin threshold voltage (vthis) vs. duty cycle(d) at fb pin = 3v for fa5528/5538 0.30 0.35 0.40 0.45 0.50 0 10 20 30 40 50 60 70 80 d (%) v t h i s ( v ) fb=3v start-up circuit vcc pin source current (ipre) vs. junction temperature (tj) -8.0 -7.5 -7.0 -6.5 -6.0 -5.5 -40 -20 0 20 40 60 80 100 120 140 tj degree) i p r e ( m a ) vvh = 100v vcc = 0v is pin threshold voltage (vthis) vs. duty cycle at fb pin = 4v and cs pin = 4v 0.40 0.45 0.50 0.55 0.60 0 10 20 30 40 50 60 70 80 d (%) v t h i s ( v ) fb=4v cs=4v is pin threshold voltage (vthis) vs. dutycycle(d) at fb pin = 2v for fa5528/5538 0.10 0.15 0.20 0.25 0.30 0 10 20 30 40 50 60 70 80 d (%) v t h i s ( v ) fb=2v http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 14 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ operating mode supply current (iccop1) vs. junction temperature (tj) 1.3 1.4 1.5 1.6 1.7 -40 -20 0 20 40 60 80 100 120 140 tj (degree) i c c o p 1 ( m a ) FA5526 / 36 fa5527 / 37 fa5528 / 38 operating mode supply current vs. vcc pin voltage (vcc) 1.3 1.4 1.5 1.6 1.7 10 15 20 25 30 vcc (v) i c c o p 1 ( m a ) FA5526 / 36 fa5527 / 37 fa5528 / 38 http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 15 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ 9. description of block circuits (1) start-up circuit the FA5526/27/28/36/37/38 has built-in start-up circuits with maximum rated voltage of 500v. wiring is shown in figs.1 to 3 . when power is turned on, a current is supplied to the vcc pin from the start-up circuit, charging the capacitor, c2, connected to the vcc pin, increasing its voltage, activating the ic, and the power supply starts operation. the current supplied to the vcc pin from the vh pin is approximately 6.8ma at vcc=0v, decreases as vcc increases and becomes approximately 6.1ma at the start-up voltage. a resistor is connected in series to the vh pin to prevent the ic from being damaged due to surge in ac and other lines. fig.1 shows the commonest wiring, connecting the vh pin to half-wave rectified ac input voltage and taking the longest start-up time of the three ways of wiring. when ac input voltage is turned off after the circuit changed to a latch mode due to overload or overvoltage protection, the latch mode can be reset in a relatively short time of several seconds because a current is not supplied from the vh pin. in fig.2 , the vh pin is connected to full-wave rectified ac input voltage, reducing start-up time to approximately half as compared to half-wave rectification circuit shown in fig.1 . the latch mode can be reset in a short time same as in fig.1 because ac input voltage is cut off. in fig.3 , the vh pin is connected to rectified and smoothed ac input voltage, resulting in the shortest start-up time of the three ways of wiring. in this way of wiring, it takes time for the latch mode to be reset because charged c1 voltage is applied to the vh pin even if the ic have changed to the latch mode. depending on usage conditions, in general it takes several minutes. when vcc pin voltage exceeds on threshold voltage of the low-voltage malfunction-protective circuit and the ic is activated, the start-up circuit is cut off and vh pin input current becomes 25ua (typ.). when ic enters to the latch mode due to any abnormal condition, the start-up circuit is activated again, the latch condition is maintained and vcc voltage is held at approximately 23v. here, FA5526/27/28 enters to the latch mode by overload or over-voltage, but fa5536/37/38 does not enter to the latch mode without an additional external circuit (see ?9.-(8)/(9) overload protection,? ?9.-(10)/(11) over-voltage protection.? ). fig.1 start-up circuit 1 (half wave) fig.2 start-up circuit 2 (full wave) fig.3 start-up circuit 3 (dc) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 16 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (2) oscillator the oscillator determines switching frequency. for steady operation at heavy load, the oscillating frequency is set at 130khz for FA5526/36, 100khz for fa5527/37 or 60khz for fa5528/38 inside the ic. in addition, the ic has a function to automatically decrease oscillating frequency at light load to reduce standby power dissipation. when fb pin voltage becomes 1.05v or less at light load, the frequency starts decreasing. at light load, as fb pin voltage drops, the frequency decreases almost linearly to the minimum operating frequency ( fig.4 ). the minimum operating frequency, fmin, is set at 1.1khz. the oscillator generates a trigger signal for determining the switching frequency, a pulse signal for determining the maximum duty cycle and a ramp signal for slope compensation. (3) current comparator and pwm latch FA5526/27/28/36/37/38 have current mode comparators. fig.5 shows a block diagram for basic operation and fig.6 a timing chart. a trigger signal is generated by the oscillator and input to the pwm latch (f.f.) as a set signal through a blanking circuit, increasing pmw latch output and also out pin voltage. on the other hand, the current comparator (is comp.) monitors a mosfet current and generates a reset signal when out pin voltage reaches the threshold voltage. then, pwm latch (f.f.) output and out pin voltage go into low state the output is controlled through varying is comparator threshold voltage due to a feedback signal. as shown in fig.7 , fb pin voltage and cs pin voltage are level-shifted and input to the current comparator (is comp.) as threshold voltage. in addition, the reference voltage of 0.52v is input to the ic to determine is pin maximum threshold voltage. the lowest of the three inputs is given a high priority. fig.4 oscillating frequency osc blanking s r q 5 3 is comp. f.f. rs is out c1 fig.5 current-mode basic operation circuit block blanking output signal (set pulse) flip flop ( f.f. ) q output ( out pin signal ) is comp. output (reset pulse) is pin voltage proportional to drain current of mosfet q1 is comp. minimum voltage among inverting input fig. 6 timing chart for current-mode basic operation http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 17 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ at start-up, soft start can be realized through gradually increasing the threshold voltage based on cs pin voltage. at steady operation, the threshold voltage is varied based on fb pin voltage to keep power supply output voltage constant. in addition, the maximum is pin threshold voltage as 520mv limits mosfet over-current when fb pin voltage is very high like 4v by overload etc. the oscillator generates a pulse to determine the maximum duty cycle of an out pulse and the maximum duty cycle is set at 80% (typ.) using this pulse.. for details, refer to ?9-(14) timing chart?. (4) blanking when mosfet turns on, a surge current is generated due to discharge current from the capacitor in the main circuit or gate drive current. if the surge current reaches the is pin threshold voltage, current comparator output could be inverted and normal pulses would not be generated from the out pin. to avoid this, a blanking function is incorporated into the current comparator. when a trigger signal is input from the oscillator, the blanking circuit outputs a certain-width pulse signal as a pwm latch (f.f.) set signal. since the set signal is given a high priority in pwm latch input signals, the output of pwm latch (f.f.) will not be inverted while the set signal is input from the blanking circuit, even if a rest signal is input from the current comparator (is comp.). as a result, the is pin input voltage is ignored for a blanking time (200ns for FA5526/36, 400ns for fa5527/37 and 600ns for fa5528/38) immediately after an output pulse has been generated from the out pin and does not respond to a surge current at turn-on. see fig.8. in general, the blanking circuit eliminates the need for a noise filter at the is pin. rs 2 1 3 buf x1 3r r20k 60k is comp. is cs fb 0.52v 11a 5v vcc cs fig.7 current comparator fig.8 blanking http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 18 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (5) minimum on pulse width as described in ?(4) blanking,? the input voltage at the is pin is ignored during a blanking period right after turn-on. consequently, the sum of blanking time and output delay time (100ns) is the minimum on pulse width at the out pin of the ic. the minimum on pulse width for FA5526/36, fa5527/37 and fa5528/38 are 300ns, 500ns and 700ns, respectively. in addition, a dedicated comparator is incorporated not to generate pulses at no load. when fb pin voltage is below 0.28v or cs pin voltage is below 0.68v, the output of the comparator is inverted and a clear signal ?clr? is input to the blanking circuit. then, the blanking circuit will not output a set signal and no set signals will be input to pmw latch (f.f.), keeping the output voltage low. (see ?9-(14) timing chart.?) (6) slope compensation in the current mode control, subharmonic oscillation may occur at a continuous current mode operation with a duty cycle of 50% or more. to avoid this, FA5526/36, fa5527/37 and fa5528/38 have built-in slope compensation circuits. for details of subharmonic oscillation phenomenon and slope compensation effect, see p.32. as shown in fig.9 , slope compensation is achieved by a input of fb pin voltage to the current comparator (is comp.), which subtracted ramp signal generated from oscillator passing through slope generator. therefore, the threshold voltage at the fb pin gradually decreases with time within each switching cycle as shown in fig.10 even when voltages at the fb pin and cs pin are constant. (see ?9-(14) timing chart.?) 5v reg. 20k 60k 7.4k 3 is comp. 0.52v 1meg 5pf vco q osc slope generator - + ( cs pin voltage ) / 4 ramp signal 2 fb is rs fig.9 slope compensation circuit fig.10 slope compensation http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 19 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (7) soft start circuit the cs pin is connected to a built-in constant current source. the current for soft start is 11ua. the capacitor externally connected to the cs pin is charged by the constant current source, gradually increasing cs pin voltage. mosfet current gradually increases at start-up because cs pin voltage is input to the current comparator (is comp.), realizing soft start. as a guide for soft start time, the time tss taken until cs pin voltage increases from 0v to 3v is given by the following equation. tss [ s ] = 0.27 * cs [ uf ] ( typical value ) here, cs is a capacitance connected to cs pin [ uf ]. in steady operation, cs pin voltage is clamped at approximately 4v by a zener diode in the ic. the cs pin is provided with a built-in circuit to stop pulses when cs pin voltage is 0.68v or less, same as fb pin. (see ?9-(14) timing chart.?) (8) overload protection of FA5526/27/28 FA5526, fa5527 and fa5528 have built-in time-latch type overload protection. fig.12 shows its block diagram and fig.13 its timing chart. in steady operation, fb pin voltage is 3v or less and cs pin voltage is clamped at 4v by a zener diode in the ic. when power supply voltage drops on account of overload or short-circuit on the load side, fb pin voltage increases. if fb pin voltage exceeds the 3.6v threshold voltage for overload protection, output voltage of a comparator for overload detection (overload) is inverted and 4v clamp of the cs pin is canceled, increasing cs pin voltage again due to a built-in constant current source. the current supplied from the cs pin becomes 4a. if the power supply voltage continues to decrease and cs pin voltage reaches the threshold voltage (8.5v) of the comparator (latch), the output of the comparator (latch) is inverted, turning off a 5v circuit in the ic and forcing out pin voltage to be low. this status is the latch mode of the ic. in the latch mode, the start-up circuit resumes operation to supply current to vcc and to hold the latch mode. 2 1 3 buf x1 3r r20k 60k is comp. is cs fb 0.52v 11a 5v vcc cs fig.11 soft start circuit enb 5v vcc 5v reg. uvlo 5v reg. enb uvlo qs r f.f. 1 11ua/4ua 8.5v/7.7v 5 6 2 4.8v 2.8v out vcc cs fb overload latch cs fig.12 overload protection circuit http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 20 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ when the output voltage momentarily drops due to abrupt load change and fb pin voltage restores to the voltage at steady state before cs pin voltage reaches 8.5v, the 4v clamp circuit restarts, producing no latch mode. the latch mode can be reset through cutting off input voltage or through forcibly decreasing cs pin voltage to 7.4v or less. cutting off the input voltage decreases vh pin voltage, supplying no current to the vcc pin. thereafter, the latch mode is reset when vcc drops below the off threshold voltage, 8.0vmin. in addition, when cs pin voltage is forcibly decreased, the latch mode comparator is re-inverted and the ic re-starts switching operation. in the case of typical ic, delay time td (olp), the time from overload detection to the latch mode, is given by the following equation. td1 (olp) [ s ] = 0.93 * cs [ uf ] ( typical value ) here, cs is a capacitance connected to cs pin [ uf ]. delay time td (olp) is inversely proportional to cs charging current and proportional to the difference between cs pin clamp voltage ?4v? at steady condition and latch-mode threshold voltage ?8.5v?. pay attention to variations in delay time resulting from variations in numerical values. in addition, be aware that when the vh pin is connected after rectification, it takes rather long time, approximately several minutes, before the latch mode is reset. (see ?9-(1) start-up circuit.?) (9) overload protection of fa5536/37/38 fa5536, fa5537 and fa5538 have built-in auto-recovery type overload protection. fig.14 shows vcc pin voltage and the drain voltage of power mosfet ?q1? in the circuit on page 33 at ?6a? overload when 90vac input is applied and fig.15 shows same parameters mentioned above at ?7a? overload when 264vac input is applied. switching period after the overload occurs and stop period are calculated as follows. steady state to overload : td2 (olp) [ s ] = td1 (olp) , after overload starts : td2 (olp) [ s ] = 1.65* cs [ uf ], stop period t (stop) [ s ] = cvcc [ uf ] * [ vcc(sw/ol) ? vccoff ] / ( i ccl ) here, vcc(sw/ol) : vcc in switching period at overload [ v ] vccoff : off threshold voltage of u.v.l.o ( 9v (typ.)) i ccl : consumption current in latch mode ( 290ua (typ.)) out pin voltage 3.6v 8.5v 8.8v short time overload overload latch off secondary side dc output voltage cs pin voltage fb pin voltage fig.13 overload protection timing chart fig.14 overload protection waveform of fa5538 as auto-recovery ( 90vac ) fig.15 overload protection waveform of fa5538 as auto-recovery ( 264vac ) vcc (20v /div) vds (100v /div) vcc (20v /div) vds (100v /div) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 21 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (10) over-voltage protection of FA5526/27/28 FA5526, fa5527 and fa5528 have built-in over-voltage protection circuits to monitor vcc voltage. fig.16 shows its block diagram and fig.17 its timing chart. when vcc voltage increases and exceeds comparator (ovp) reference voltage, 28v, an internal 1.3ma constant current source is tuned on. since sink capability of the zener diode which clamps the cs pin at 4v is 55ua, cs pin voltage quickly increases when the 1ma constant current source is turned on. when cs voltage exceeds comparator (latch) reference voltage, 8.5v, the ic changes to the latch mode. the delay time td (ovp), the time from over-voltage detection to the latch mode, is given as follows. td (ovp) [ ms ] = 2.85 * cs [ uf ] ( typical value ) here, cs is a capacitance connected to cs pin [ uf ]. in the latch mode, an internal power supply source, 5v ?reg? circuit, is turned off and out pin voltage is held to be low., and the current form the cs pin changes to 5a. the latch mode can be reset through decreasing vcc voltage due to cutting off of input voltage or through forcibly decreasing cs pin voltage to 7.4v or less. moreover, pay attention to the relationship between wiring at the vh pin and reset time in the latch mode. see ?9-(1) start-up circuit.? (11) over-voltage protection of fa5536/37/38 fa5536, fa5537 and fa5538 have built-in over-voltage protection ( ovp ) circuits to monitor vcc voltage similar to FA5526/27/28. however, the ovp of fa5536/37/38 is auto-recovery mode . therefore, when you need the ovp as latch mode, the additional external circuit is necessary as mentioned on page 28 to 29 ( see ?10-(4)? ). (12) u nder-v oltage l ock-o ut circuit the ic has a built-in undervoltage lockout circuit to prevent malfunction when vcc voltage drops. when vcc voltage increases from 0v, the ic starts operation at vcc = 15v (typ.). as the supply voltage decreases, the ic stops operation at vcc = 9v(typ.). when the undervoltage lockout circuits operates and the ic stops operation, out pin and cs pin voltage are forced to be low, resetting soft start, and overload and overvoltage timer latch protection. enb 5v vcc 5v reg. uvlo 5v reg. enb uvlo qs r f.f. 1 1.3ma 8.5v/7.7v 5 6 2 4.8v 2.8v out vcc cs fb overload latch 28v ovp cs fig.16 over voltage protection circuit ( only for FA5526 / 5527 / 5528 ) fig.17 over-voltage protection timing chart ( only for FA5526 / 5527 / 5528 ) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 22 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (13) output circuit the output circuit consists of push-pull configuration, capable of directly driving a mosfet. the maximum peak currents at the out pin are 0.25a for source current and 0.5a for sink current. if the ic stops operation when the under-voltage lockout circuit operates or in the latch mode, out pin voltage is forced to be low to shut down the mosfet. (14) timing chart oscillator (osc) trigger (t) output blanking clr signal blanking output signal (set pulse) fb pin voltage is pin voltage is comp. output (reset pulse) ff q output osc q output out pin output voltage blanking time fig.18 timing chart at steady operation http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 23 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ oscillator (osc) trigger (t) output blanking clr signal blanking output signal (set pulse) fb pin voltage is pin voltage is comp. output (reset pulse) ff q output osc q output out pin output voltage 0.36v oscillator (osc) trigger (t) output blanking clr signal blanking output signal (set pulse) fb pin voltage is pin voltage is comp. output (reset pulse) ff q output osc q output out pin output voltage fig.19 timing chart at maximum duty cycle operation fig.20 timing chart at fb pin < 0.36v http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 24 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ minimum on width ( the sum of blanking time and delay time to out pin ) blanking time oscillator (osc) trigger (t) output blanking clr signal blanking output signal (set pulse) fb pin voltage is pin voltage is comp. output (reset pulse) ff q output osc q output out pin output voltage cs pin voltage ( cs pin voltage ) / 4 ( cs pin voltage ) / 4 determines on width as high voltage period of out pin fig.21 timing chart at start-up (soft start) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 25 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ 10 design advice (1) start-up and stop to properly start up and stop the power supply, optimum values shall be set for capacitors connected to the cs pin and vcc pin. (1-1) at start-up (1) it takes certain time until the output voltage reaches to the set voltage after the ic has been activated. during this period, fb pin voltage reaches its maximum voltage and the 4v clamp circuit does not operate. as a result, with proper cs pin capacitance and proper start-up, cs pin voltage waveform during start-up will be as shown in fig.22 . on the other hand, when cs pin capacitance is too small, cs pin voltage may reach the threshold voltage of the latch mode as shown in fig.23 before the output voltage increases to the set value. the ic changes into a latch mode and the power supply cannot start properly. in cases like this, increase cs pin capacitance. (1-2) at start-up (2) fig.24 shows vcc voltage at start-up when proper capacitance is connected. when input power is turned on, the vcc capacitor is charged by the current supplied from the start-up circuit and its voltage increases. then, when vcc reaches the on threshold voltage, the ic starts operation. in steady operation, the ic operates at the voltage supplied from an auxiliary winding. right after ic start-up, however, vcc drops until the auxiliary voltage increases sufficiently. determine the capacitance connected to vcc pin so that vcc does not drop to the off threshold voltage in any condition. we recommend that you choose the capacitance connected to vcc pin so that the bottom of vcc becomes larger than 11v as the result of typical experiment. secondary side dc output voltage cs pin voltage fb pin voltage 8.5v start-up of ic 4v a) after cs pin exceeds 4v, fb pin voltage drops. start-up of ic 3v b) before cs pin exceeds 4v, fb pin voltage drops. fig.22 cs pin voltage waveform at start-up (1) ( normal start ) 8.5v latch mode secondary side dc output voltage cs pin voltage fb pin voltage start-up of ic dc output set voltage fig.23 cs pin voltage waveform at start-up (2) when the power supply can not start up fig.24 vcc waveform at start-up (1) at normal start-up http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 26 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ when vcc capacitance is too small, vcc drops to the off threshold voltage as shown in fig.25 before the auxiliary winding voltage increases sufficiently. in this case, vcc repeatedly goes up and down between the on and off threshold voltages, and the power supply can not start up. (1-3) at stopping when the power supply is turned off by shutdown of input voltage, output voltage remains low for certain period of time before the ic stops operation. during this period, fb pin voltage increases and the cs pin clamp circuit is cancelled because output voltage remains low. as a result, cs pin voltage increases as shown in fig.26 . cs pin voltage shall not reach the threshold voltage of the latch mode. as shown in fig.27 , if cs pin voltage reaches the threshold voltage, the latch mode is held for a period of time until vcc capacitor voltage drops to off threshold voltage. as a result, the power supply cannot be re-started even if input voltage is turned on again. in such a case, the following measures shall be taken: ? reduce the time taken until the ic stops operation after the output voltage has dropped through reducing vcc capacitance. ? suppress cs pin voltage rise through increasing cs pin capacitance. (2) hold time of vcc in some cases, vcc pin capacitance shall be increased to hold vcc above the off threshold voltage at abrupt load change after the power supply has started up. however, when vcc pin capacitance becomes larger, start-up time gets longer. in such a case, the circuit shown in fig.28 is effective. reducing c2 shortens start-up time, and hold time can be kept long because power is supplied via c4 after start-up. fig.28 vcc circuit fig.25 vcc waveform at start-up (2) when the power supply can not start up vcc pin voltage 8.5v secondary side dc output voltage cs pin voltage fb pin voltage off threshold voltage ( 9v ) fig.26 waveform at stopping (1) 8.5v latch mode ( the period when ic can not re-start ) vcc pin voltage secondary side dc output voltage cs pin voltage fb pin voltage off threshold voltage ( 9v ) fig.27 waveform at stopping (2) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 27 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (3) protection using cs pin for FA5526/27/28 in steady operation, the cs pin voltage is clamped by a 4v zener diode. externally forcing cs pin voltage to increase to the threshold voltage, 8.5v, for the latch mode allows the ic to stop its operation for protection. in this case, a current of more than the sink capacity of 4v zener diode, 84ua, shall be applied to the cs pin. set the input current to the cs pin at 1ma or less as a guide. the following shows examples of overvoltage protection at an arbitrary voltage using the cs pin. (3-1) overvoltage detection on the secondary side fig.29 shows an example of an overload detection circuit on the secondary side to change the ic into the latch mode. (3-2) detection of vcc (1) fig.30 shows a circuit where the ic is stopped in the latch mode upon detecting vcc overvoltage. in this case, vcc voltage is latched at approximately zd+8.5v. use a zd whose voltage is larger than the on threshold voltage of the low-voltage malfunction preventive circuit. otherwise, the ic cannot start. (3-3) detection of vcc (2) fig.31 shows another circuit to detect vcc overvoltage. in this case, vcc voltage is latched approximately at zd voltage. use a zd whose voltage is larger than the on threshold voltage of the low-voltage malfunction preventive circuit. otherwise, the ic cannot start. (4) protection using cs pin for fa5536/37/38 fa5536/37/38 does not include any latch function. therefore, the external latch circuit is necessary for o ver-v oltage p rotection as latch mode. fig.32 shows the ovp latch circuit by primary side detection at vcc pin and fig.33 shows the ovp latch circuit by secondary side detection through a optocoupler ?pc?. when cs pin voltage is pulled down below 0.68v ( typ. ), the switching is shut-down. once the npn transistor ?q2? and ?q3? turn-on when the diode ?zd1? or optocoupler ?pc? supplies the current to resistor ?r1? by detection of over-voltage, pnp transistor ?q1? turns-on and ?q2? and ?q3? are maintained in on-state. then, cs pin voltage is maintained at low level until the current of a diode zd2 is cut vcc pin voltage decreases below off threshold ( 9v ) . fig.29 over voltage protection (1) for FA5526/27/28 fig.30 over voltage protection (2) for FA5526/27/28 fig.31 over voltage protection (3) for FA5526/27/28 fig.32 over voltage protection (1) for fa5536/37/38 http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 28 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (5) when not using an overload protection function as shown in fig.34 , connect a resistor r3 of 18k ohm between fb pin and gnd. as a result, fb pin voltage does not increase to the threshold voltage for overload protection and the ic does not change to the latch mode even at overload. in this case, the latch protection for over-voltage is also available. (6) correction of overload detection current ( line conversation ) if the power supply output becomes overload, the current of the mosfet is limited by the maximum threshold voltage of the is pin and power supply voltage drops. if the state continues as it is, an overload protection function operates to stop the ic in the latch mode. for details of an overload protection function, see ?9-(8) overload protection function.? when the overload protection operates, the output current of the power supply varies depending on the input voltage; and the higher the input voltage is, the larger the output current. in such a case, connect r4 between the current detection resistor rs and is pin, and add a correction resistor r5 as shown in fig.35 . the typical resistance of r5 is several hundreds of k ohm to several meg ohm. note that the above correction slightly decreases the value of overload current limit to stop the ic in the latch mode even if input voltage is low. fig.33 over voltage protection (2) for fa5536/37/38 fig.34 when not using overload protection fig.35 correction of overload detection current ( line conversation ) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 29 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (7) improvement of input power at light load this ic is provided with a function to lower switching frequency at light load in order to reduce power dissipation. however, depending on the circuit used, switching frequency cannot be sufficiently reduced, leading to insufficient reduction of power dissipation at light load. in such a case, connect r6 between the auxiliary winding and the is pin as shown in fig.36 . when r4 is 1k ohm, r6 is several hundreds of k ohm to 1meg ohm. the smaller the r6 is, the lower the switching frequency at light load. however, negative voltage is applied to the is pin due to r6 for some time while mosfet is on. be aware that the negative voltage shall not be lower than absolute maximum rationg,-0.3v. in addition, when switching frequency is set too low at light load, transformer or other apparatus may produce noise. (8) prevention of malfunction caused by noise this ic is an analog ic, and noise applied to anyone of the pins may cause malfunction. if malfunction is detected, use the ic through referring to the following description and fully checking a power supply unit. in addition, arrange the capacitors connected to pins as close to the ic as possible and take great care of wiring, for effective noise suppression. (8-1) fb pin the fb pin sets the threshold voltage of the current comparator. any noise applied to the fb pin may disturb output pulses. usually the capacitor c5 is connected as shown in fig.37 to suppress noise. (8-2) is pin as described in ?9.-(4) blanking,? this ic has a blanking function, and malfunction caused by a surge current produced at turn-on of the mosfet is hard to occur. a malfunction, however, may occur when a surge current is excessively large or when any noise is externally applied at other than turn-off. in such a case, add a cr filter to the is pin as shown in fig.38 . (8-3) vcc pin relatively large noise may occur at the vcc pin because a large current flows from the vcc pin at the instant of driving the mosfet. if noise is excessively large, a malfunction may occur of the ic. pay full attention to capacitance and characteristics of the capacitor between the vcc pin and gnd to reduce noise as much as possible. fig.36 input power improvement circuit at light load fig.37 prevention of malfunction caused by noise (fb pin) fig.38 prevention of malfunction caused by noise (is pin) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 30 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (9) over temperature protection as latch mode for FA5526 / 27 / 28 over temperature protection as latch mode can be achieved by the circuit shown in fig.39 for FA5526/27/28. here, a diode d1 connected to separated line from vcc pin, because the start-up time of ic may become too long when the circuit including a thermistor is connected to vcc pin of ic directly. please note that the circuit shown in fig. 39 can not be used for fa5536/37/38, because fa5536/37/38 does not include any latch function. (10) prevention of malfunction caused by negative voltage applied to pins when a large negative voltage is applied to a pin, a parasitic element in the ic may operate and cause a malfunction. be sure that voltage applied to a pin shall not be -0.3v or less. voltage oscillation generated at turn-off of the mosfet may be applied to the out pin via the parasitic capacitance of the mosfet, resulting in the negative voltage applied to the out pin. in such a case, connect a shottky diode between each pin and gnd. forward voltage of the shottky diode can suppress negative voltage at each pin. use a shottky diode with low forward voltage. fig.40 shows an example of a circuit with a shottky diode connected to the out pin. (11) gate circuit configuration a resistor is generally inserted between the gate terminal of the mosfet and the out pin of the ic for adjustment of switching speed, suppression of voltage oscillation at the gate terminal and other purposes. sometimes, the drive currents for turning-on and -off must independently determined. in such a case, connect the gate terminal of the mosfet and out pin of the ic as shown in fig.41 or fig.42 . in fig.41 , the driving current is limited by rg1 + rg2 at turn-on and by only rg2 at turn-off in fig.42 the driving current is limited by only rg1 at turn-on and by parallel-connected rg1 and rg2 at turn-off. fig. 39 o ver t emperature p rotection by latch mode for FA5526 / 5527 /5528 note : otp latch by fa5536 / 5537 / 5538 can not be achieved by above circuit. fa5536 / 5537 / 5538 may need very complicated circuit for otp latch. fig.40 negative voltage prevention circuit fig.41 gate circuit (1) fig.42 gate circuit (2) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 31 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (12) loss calculation ic loss shall be determined to use the ic within its rating. since it is hard to directly measure ic loss, an example of calculating approximate ic loss is given below. total ic loss, pd, is obtained by the following equation: pd = vcc * ( iccop1 + qg * f ) + v vh * ihrun where vcc is the supply voltage to the ic, iccop1 is consumption current of the ic, qg is total gate charge of the mosfet, f is switching frequency, v vh is vh pin voltage and ihrun is a current flowing into the vh pin when the ic operates. this equation gives an approximate value of pd, which is a little greater than the actual loss. take into consideration variation and temperature characteristics of each value (example) when the vh pin is connected to half-wave rectification waveform at power supply of 264vac, the average vh pin voltage is approximately 119v. under above condition, let us suppose vcc = 18v and qg = 80nc at tj = 25 degree. when using fa5528 or fa5538, according to the specifications ihrun = 25ua = 0.025ma ( typ. ), iccop1 = 1.4ma ( typ. ) and f = 60khz = 0.06mhz ( typ.). thus, typical ic loss pd: pd = 18v * ( 1.4ma + 80nc * 0.06mhz ) + 119v * 0.025ma = 115mw ( typ. ) http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 32 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ (reference) sub-harmonic oscillation and slope compensation in a peak-value-control current mode, when the converter operates in an inductor-current continuous mode and at duty cycle of 50% or more, the current may oscillate at an integral multiple of switching frequency. this oscillation is called subharmonic oscillation. fig. 43 shows an example of inductor current waveform when a subharmonic oscillation occurs. it is found that on and off periods vary while the peak value of an inductor current, switching cycle and current slopes during on and off periods remain unchanged. the harmonic oscillation may increase ripple voltage contained in the output voltage or cause an unusual noise. the subharmonic oscillation can be prevented by giving a certain gradient to the threshold of the peak current as shown in fig. 44 . this is called slope compensation. generally, the gradient of slope compensation required for preventing a subharmonic oscillation is given by the following relational expression: 2 luld kc ? ? here, lu gradient of an inductor current during the on period ld gradient of an inductor current during the off period kc gradient of slope compensation the above parameters are shown in fig.45 . fig.43 inductor current without slope compensation fig.44 inductor current with slope compensation fig.45 inductor current without slope compensation http://www..net/ datasheet pdf - http://www..net/
an-087e rev.1.0 april-2011 33 FA5526/5527/5528/5536/5537/5538 fuji electric co., ltd. http://www.fujielectric.co.jp/products/semiconductor/ 11. example of an application circuit the following circuit is common to both of fa5528 and fa5538 . FA5526/27/28/36/37/38 can be used for same topology except the protection circuit and the transformer design which depends on switching frequency. note : the example of an application circuit is intended to be used only for reference and not to guarantee performance or characteristics. input power at no-load 0 50 100 150 200 250 50 100 150 200 250 300 line voltage (vac) i n p u t p o w e r ( m w ) efficiency (io=5a) 81 82 83 84 85 86 87 88 89 90 50 100 150 200 250 300 line voltage (vac) e f f i c i e n c y ( % ) switching frequency at no-load 0 5 10 15 20 25 50 100 150 200 250 300 line voltage (vac) f s w ( k h z ) over current protection vs. ac line voltage 4.0 4.5 5.0 5.5 6.0 6.5 7.0 80 100 120 140 160 180 200 220 240 260 280 ac line voltage ( v) d c o u t p u t c u r r e n t a t o c p http://www..net/ datasheet pdf - http://www..net/

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