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1 www.semtech.com sc4911 bias/primary side pwm controller with ultra low start-up current power management revision: april 5, 2006 description features applications typical application circuit ? programmable switching frequency up to 500khz ? line uvlo protection ? undervoltage lockout ? low startup current (45a) ? cycle by cycle current limit ? 8 pin msop. available in lead-free, fully weee and rohs compliant the sc4911 is a highly integrated bias/primary side pwm controller designed for off-line or isolated dc-dc convert- ers in telecommunication and data communication ap- plications. the high degree of integration minimizes the amount of discrete parts needed and leads to substan- tial cost and space saving converter designs. the circuitry of the sc4911 includes line voltage uvlo featuring startup current less than 50a and program- mable switching frequency. the device supply is derived from an auxiliary winding on the transformer. the auxil- iary winding could also provide output feedback informa- tion if an optocoupler is not used. vout r5 r9 c3 r1 r7 c6 d2 c2 d1 u1 sc4911 1 2 3 4 5 6 7 8 luvlo rt fb comp ilim gnd out vcc c4 r4 vin c7 c1 r8 r2 q1 r6 t1 c8 r3 c5 ? telecom isolated converters ? offline isolated power supplies ? instrumentation power supplies ? battery chargers
2 ? 2006 semtech corp. www.semtech.com sc4911 power management absolute maximum ratings electrical characteristics r e t e m a r a ps n o i t i d n o c t s e tn i mp y tx a mt i n u y l p p u s r e w o p e g a t l o v n o - n r u t c c v 0 . 60 . 7v t n e r r u c g n i t a r e p of s d a o l o n , z h k 0 0 2 =4 . 30 . 5a m t n e r r u c p u t r a t so l v u l=v 6 . 05 40 8a e g a t l o v t n u h s r e n e z c c vi c c a m 0 1 =5 16 17 1v o l v u e n i l d l o h s e r h t t u o k c o l 2 2 . 15 2 . 18 2 . 1v s i s e r e t s y h o l v u 0 7v m t n e r r u c s a i bv o l v u l v 5 2 . 1 <0 0 1a n r e i f i l p m a r o r r e e g a t l o v t u p n i k c a b d e e fv c c v 2 1 =4 4 . 20 5 . 26 5 . 2v n o i t a l u g e r e g a t l o v t u p n i k c a b d e e fv c c v 2 1 o t v 7 =5 2 4 . 25 7 5 . 2v t n e r r u c s a i b t u p n i 0 7 1a n e c n a t c u d n o c s n a r t r e i f i l p m a 0 0 0 1o h m t n e r r u c e c u o s r e i f i l p m a 0 0 5a t n e r r u c k n i s r e i f i l p m a 0 0 6a n i a g e g a t l o v p o o l n e p o 0 5b d r e t e m a r a pl o b m y sm u m i x a ms t i n u e g a t l o v y l p p u sv c c 8 1v t n e r r u c y l p p u si c c 0 2a m e g a t l o v o l v u e n i l v c c v p m o c d n a m i l i , b f 6 o t 3 . 0 -v k n i s r o e c r u o s t n e r r u c t u p t u o 0 5 2a m e g n a r e r u t a r e p m e t e g a r o t st g t s 0 5 1 + o t 0 6 -c e g n a r e r u t a r e p m e t n o i t c n u jt j 0 5 1 + o t 0 4 -c . c e s 0 1 ) g n i r e d l o s ( e r u t a r e p m e t d a e lt d a e l 0 6 2c ) l e d o m y d o b n a m u h ( g n i t a r d s ed s e2v k unless specified: t a = t j = -40c to +125c, v cc = 12v, r t = 100k ?, v fb = 2.4v, luvlo = 1.5v. exceeding the specifications below may result in permanent damage to the device, or device malfunction. operation outside of th e parameters specified in the electrical characteristics section is not implied.
3 ? 2006 semtech corp. www.semtech.com sc4911 power management electrical characteristics (cont.) r e t e m a r a ps n o i t i d n o c t s e tn i mp y tx a mt i n u r o t a l l i c s o e g n a r y c n e u q e r fr t k 0 0 2 = ? 0 0 1 z h k r t k 3 4 = ? 0 0 5 y c n e u q e r f 0 7 10 0 20 3 2z h k e l c y c y t u d e l c y c y t u d m u m i x a m 7 55 62 7% e l c y c y t u d m u m i n i mv b f v 3 =0% t i m i l t n e r r u c d l o h s e r h t t i m i l t n e r r u c 0 0 55 2 50 5 5v m e t a g o t y a l e d n o i t a g a p o r p 0 7s n t u p t u o e t a t s w o l e g a t l o v t u p t u oa m 5 k n i s1 . 05 . 0v e t a t s h g i h e g a t l o v t u p t u oa m 5 e c r u o s5 . 92 . 0 1v e m i t e s i rc t u o f p 0 0 1 =5 2s n e m i t l l a fc t u o f p 0 0 1 =0 1s n unless specified: t a = t j = -40c to +125c, v cc = 12v, r t = 100k ?, v fb = 2.4v, luvlo = 1.5v.
4 ? 2006 semtech corp. www.semtech.com sc4911 power management pin configuration ordering information pin descriptions r e b m u n t r a pe g a k c a pt ( e g n a r . p m e t j ) r t s m i 1 1 9 4 c s 8 - p o s m ) 1 ( c 5 2 1 + o t c 0 4 - t r t s m i 1 1 9 4 c s ) 2 ( notes: (1) only available in tape and reel packaging. a reel contains 2500 devices. (2) lead free product. this product is fully weee and rohs compliant. ilim gnd out vcc comp fb rt luvlo # n i pe m a n n i pn o i t c n u f n i p 1o l v u l. t u o k c o l e g a t l o v r e d n u e n i l 2t r. y c n e u q e r f r o t a l l i c s o g n i m m a r g o r p r o f 3b f. k c a b d e e f 4p m o c. n o i t a s n e p m o c k c a b d e e f 5m i l i. e s n e s t i m i l t n e r r u c 6d n g. d n u o r g 7t u o. o l v u l r o o l v u g n i r u d w o l . t u p t u o e v i r d e t a g 8c c v. e g a t l o v y l p p u s (msop- 8 pin) top view part number code (example: aaxx) yyww = date code (example: 0012) xxxx = semtech lot no. (example: e901 xxxx 01-1) marking information
5 ? 2006 semtech corp. www.semtech.com sc4911 power management block diagram + - pwm compar ator fb + - log i c or g ate gnd oscillator er r or ampl i fi er bandgap output driver comp uvlo comp pwm latch & vt 0.5v rt star tup vcc il i m compar ator ilim + - out l- uvl o 0.525v
6 ? 2006 semtech corp. www.semtech.com sc4911 power management the sc4911 is a voltage mode controller designed mainly for the isolated or non-isolated flyback converters. as shown in the block diagram, it includes start-up circuit, bandgap, error amplifier, pwm comparator, logic and output stage. line undervoltage has dual functions of line voltage lockout and shutdown. when luvlo is pull down to ground, the sc4911 is disabled and the quies- cent current is reduced to typical 30a. when it is con- nected to a resistor voltage divider between input volt- age and ground, it monitors the line voltage. oscillator the switching frequency of the sc4911 is set by an ex- ternal resistor connected between rt and gnd. figure 1 shows the relationship between the resistance of the external resistor and the switching frequency. figure 1. timing resistor vs oscillator frequency timing resistor vs switching frequency 0 50 100 150 200 250 100 200 300 400 500 frequency ( khz ) resistance ( kohms ) line uvlo and vcc uvlo the line uvlo monitors the input line voltage and vcc uvlo monitors the supply voltage to the sc4911. if ei- ther input line or vcc is below the lockout threshold, the output is held low and the supply current to the chip is typically 30a. a resistor divider from the input line to gnd determines the desired undervoltage lockout level. to prevent noise coupling to affect proper uvlo operation, a small capaci- tor, one hundred to a few hundred pf, is recommended to be used from line uvlo pin to gnd. start-up as shown in typical applications circuit on the front page, when input voltage is applied, c1 is trickle charged through the start-up resistor r1 until the sc4911 vcc reaches the turn-on voltage. applications information the bias current consumed by the device during this pe- riod is only typical 30a. once vcc exceeds the turn-on voltage, out starts driving the mosfet, transferring en- ergy to the secondary and the bias output. if the bias output voltage builds to and is above the vcc turnoff voltage, the start-up is completed and normal operation begins. the size of the start-up resistor not only affects power supply start-up time, but also power supply efficiency. the resistor dissipates continuous power in normal op- eration. due to ultra low start-up current of the sc4911, large value resistor (several hundred kohm to 1mohm) could be used, particularly for off-line applications to improve efficiency considering reasonable start-up time. current limit the current sense resistor is selected by dividing the cur- rent sense threshold voltage 0.525v by the primary peak current at the desired current limit point, typically 120% of the primary peak current. pk sense i 2 . 1 v 525 . 0 r = care must be taken to ensure proper selection of sense resistor and good layout to prevent erratic operation. the non-inductive resistor must be used as the sense resis- tor. parasitic inductance in series with the sense resistor must be minimized. additional rc filter may be neces- sary to eliminate the narrow spike time on the leading edge of the primary current. the rc time constant can be chosen to be equal to the time constant of the sense resistor and the parasitic inductance. pcb layout long power supply and ground traces should be avoided. a 0.1 f ceramic capacitor closely placed between vcc and gnd is recommended. the timing resistor used to program switching frequency should be located close to pin rt and pin gnd in order to have a stable switching frequency. mosfet should be located near the device and a resistor in the range of several ohms could be used in series with the gate drive to damp the ringing if the trace between the drive output and mosfet is not short enough. star ground connection is recommended to avoid ground loops. the power path for input filter, mosfet and transformer should be separated from signal path for timing resistor and feedback resistor, and both should be brought to a single ground point.
7 ? 2006 semtech corp. www.semtech.com sc4911 power management 48v to 12v flyback converter as auxiliary supply figure 2 shows a simple bias supply using the sc4911. this 36 - 72v input flyback power supply employs primary side regulation from the transformer bias winding, which eliminates the need of opto coupler and secondary reference error amplifier. this is best for low cost applications requiring isolation and narrow load variation range on the secondary. during the start-up, the input source trickle charges the capacitor c1 through start-up resistor r1. as long as voltage across c1 reaches the vcc turn-on threshold, the sc4911 turns on abruptly and start driving the gate of mosfet q1. after the sc4911 starts up the primary bias winding supplies the primary circuitry. typical applications the output of the t1 bias winding is rectified, filtered by c1 and is fed to the fb through feedback resistor r5 and r7. the output voltage on the secondary is proportional to the bias voltage by the turns ratio of the output to the bias winding. c7 and r9 are for frequency compensation. an additional small capacitor could be used from comp to gnd if it is needed. the luvlo pin monitors the input voltage via resistor r2 and r4 to determine turn-on and turn-off of the converter. capacitor c5 helps filter out the noise from the input line. figure 2. 48v to 12v flyback converter as auxiliary supply r1 100k c7 47nf vin = 48v vpri = 12v r4 100k r2 2.7meg c5 100pf r9 4.7k c8 1000pf d1 1n5819 vo = 12v q1 si2320ds u1 sc4911 1 2 3 4 5 6 7 8 luvlo rt fb comp ilim gnd out vcc t1 3 5 8 10 2 1 r8 1.00 c3 10uf d2 1n5819 r7 100k r5 383k r3 68 r6 51 c4 0.1uf c6 150pf c1 10uf c2 100uf r10 100k
8 ? 2006 semtech corp. www.semtech.com sc4911 power management typical applications (cont.) isolated feedback 48v to 12v application figure 3 gives an example of isolated feedback and low power flyback application of the sc4911. t1 is a three winding transformer. the winding 1-2 is a bias winding which supplies the primary circuitry after the sc4911 starts up. during the startup, the input source trickle charges the capacitor c1 through the start-up resistor r1. as long as voltage across c1 reaches the vcc turn- on threshold, the sc4911 turns on abruptly and start driving the gate of mosfet q1. as q1 starts switching, regenerative feedback from the bias winding will provide current via d1 to capacitor c1. in this configuration, the input voltage is in the range of 36v to 72v for telecom applications, and the luvlo pin monitors the input voltage via resistor r2 and r5 to determine turn-on and turn-off of the converter. capacitor c5 helps filter out the noise from the input line. timing resistor r13 sets switching frequency. r3 and c6 are used to suppress the voltage spikes across the switch due to leakage inductance of t1. r11 is current sense resistor to set current limit of the convertor. r10 and c9 filter spikes caused by parasitic capacitance during the turning on of q1. the u3 sc431 is shunt regulator integrating an accurate 2.5v bandgap reference, op amp and driver into a single device. it compares sensed output voltage divided by r7 and r9 to its internal reference and drives the amplified error signal to opto-coupler u1. c7 keeps ripple and noise from over driving the device. u1 delivers the isolated feedback signal to the sc4911. c8 and r12 are for compensation. an additional small capacitor could be used from comp to gnd if needed. d2 1n5819 c2 100uf d1 1n5819 c5 100pf q1 si2320ds r12 4.7k r7 10k c7 220pf r2 2.7meg r10 51 r5 100k r9 10k c1 10uf nec2501 u1 c9 1000pf vin = 48v c8 47nf r4 330 c4 0.1uf r11 1.00 r13 100k r3 68 r1 100k vo = 5v c3 10uf u3 sc431 c6 150pf r6 1k r8 1k u2 sc4911 1 2 3 4 5 6 7 8 luvlo rt fb comp ilim gnd out vcc t1 3 5 8 10 2 1 figure 3. isolated 48v to 12v flyback converter
9 ? 2006 semtech corp. www.semtech.com sc4911 power management non-isolated feedback 48v to 12v application figure 4 is an example of low cost, non-isolated feedback, low power application of the sc4911. t1 is a two winding transformer. the output voltage is directly fed to the primary circuitry. during the start-up, the input source trickle charges the capacitor c3 through start-up resistor r1. as long as the voltage across c3 reaches the vcc turn-on threshold, the sc4911 turns on abruptly and starts driving the gate of mosfet q1. after the sc4911 starts up the secondary winding supplies the primary circuitry. in this 36v to 72v telecom application, luvlo monitors the input voltage via resistor r2 and r4 to determine turn-on and turn-off of the converter. capacitor c4 helps filter out the noise from the input line. voltage feedback is directly brought from the output to the input error amplifier of sc4911 through r5 and r7. c6 and r9 are for frequency compensation. an additional small capacitor could be used from comp to gnd if needed. typical applications (cont.) vo = 12v c6 47nf c4 100pf d1 1n5819 q1 si2320ds c5 150pf u1 sc4911 1 2 3 4 5 6 7 8 luvlo rt fb comp ilim gnd out vcc c1 47uf r6 51 c3 10uf r7 100k t1 c7 1000pf r4 100k d2 1n5819 r8 1.00 c2 10uf r1 100k r9 4.7k r2 2.7meg r3 68 r5 383k vin = 48v r10 100k figure 4. non-isolated 48v to 12v flyback converter
10 ? 2006 semtech corp. www.semtech.com sc4911 power management typical applications (cont.) 48v to 12v flyback converter as battery charger figure 5 is another example of non-isolated feedback, low power and compact application of the sc4911 as a battery charger. battery charging rate is determined by current sense resistor r8. luvlo is used to not only turn on or turn off the charger by battery charge controller, but also monitors the input line voltage via resistor r2 and r5 to determine turn-on and turnoff of the converter. during the start-up, the input source trickle charges the capacitor c3 through start-up resistor r1. as long as voltage across c3 reaches the vcc turn-on threshold, the sc4911 turns on abruptly and starts driving the gate of mosfet q1. after the sc4911 starts up the secondary winding supplies the primary circuitry. q1 si2320ds c4 150pf r3 68 to battery charger controller u1 sc4911 1 2 3 4 5 6 7 8 luvlo rt fb comp ilim gnd out vcc c6 1000pf r7 100k r8 1.00 d1 1n5819 r2 2.7meg t1 r10 100k r6 51 vin = 48v c3 10uf r9 4.7k to 12v battery r4 619k d2 1n5819 c1 47uf r1 100k c2 10uf c5 47nf r5 100k figure 5. 48v to 12v flyback converter as battery charger in this application, voltage feedback is directly brought from the output to the input error amplifier of sc4911 through r4 and r7. c5 and r9 are for frequency compensation.
11 ? 2006 semtech corp. www.semtech.com sc4911 power management r6 0 u1 sc4911 1 2 3 4 5 6 7 8 luvlo rt fb comp ilim gnd out vcc c6 470pf r9 1.00 c8 47nf t1 31414r 3 4 5 8 2 1 d1 1n5819hw j3 vb=12v 1 2 c4 10uf/100v r4 100k r5 383k c7 150pf/100v r3 68 c1 47uf c9 1000pf c5 10uf c2 47uf j2 vin=48v 1 2 q1 si2320ds r8 100k r11 100k r7 51 j1 vo=12v 1 2 c3 47uf d2 b150 c10 470pf r10 4.99k r1 100k r2 2.7meg d3 1n5819hw evaluation board schematic
12 ? 2006 semtech corp. www.semtech.com sc4911 power management m e t iy t i t n a u qe c n e r e f e rn o i t p i r c s e d / t r a p# r e r u t c a f u n a mt n i r p t o o f 13 3 c , 2 c , 1 cf u 7 4m 7 4 b p t 6 13 4 3 7 t c / m s 214 cv 0 0 1 / f u 0 10 0 1 a 2 c f - u e e1 3 0 . / 0 0 1 . s l / 0 5 2 . d / l y c 315 cf u 0 1l 1 3 c k 6 0 1 c 1 6 r e 2 3 m r g0 1 2 1 c / m s 416 cf p 0 7 45 0 8 0 c / m s 617 cv 0 0 1 / f p 0 5 15 0 8 0 c / m s 62 0 1 c , 8 cf n 7 45 0 8 0 c / m s 719 cf p 0 0 0 15 0 8 0 c / m s 82 3 d , 1 dw h 9 1 8 5 n 13 2 1 d o s 912 d3 1 - 0 5 1 ba m s / m s 0 111 qs d 0 2 3 2 i s1 t - s d 0 2 3 2 i s3 2 - t o s 1 14 1 1 r , 8 r , 4 r , 1 rk 0 0 15 0 8 0 r / m s 2 112 rg e m 7 . 25 0 8 0 r / m s 3 113 r8 65 0 8 0 r / m s 4 115 rk 3 8 35 0 8 0 r / m s 5 116 r0 5 0 8 0 r / m s 6 117 r1 55 0 8 0 r / m s 7 119 r1 5 0 8 0 r / m s 8 110 1 rk 9 9 . 45 0 8 0 r / m s 9 111 tr 4 1 4 1 3m o c d i mr 4 1 4 1 3 0 211 ur t s m i 1 1 9 4 c s . p r o c h c e t m e s 1 1 1 2 - 8 9 4 - 5 0 8 8 - p o s m evaluation board schematic- bom
13 ? 2006 semtech corp. www.semtech.com sc4911 power management typical characteristics vcc turn-on voltage vs temperature 5.10 5.20 5.30 5.40 5.50 5.60 5.70 5.80 -40 -20 0 20 40 60 80 100 120 temperature (c) turn on voltage (v) line uvlo lockout threshold vs temperature 1.236 1.237 1.238 1.239 1.240 1.241 1.242 1.243 1.244 1.245 -40 -20 0 20 40 60 80 100 120 temperature (c) lockout thre shold (v) error amplifier feedback voltage vs temperature 2.490 2.495 2.500 2.505 2.510 2.515 2.520 2.525 -40 -20 0 20 40 60 80 100 120 temperature (c) feedback input voltage (v) oscillator frequency vs temperature 190.00 191.00 192.00 193.00 194.00 195.00 196.00 197.00 198.00 199.00 200.00 -40 -20 0 20 40 60 80 100 120 temperature (c) frequency (khz) rt = 100k max. duty cycle vs temperature 63.00 63.50 64.00 64.50 65.00 65.50 66.00 66.50 -40-200 20406080100120 temperature (c) max. duty cycle (%) current limit threshold vs temperature 520 521 522 523 524 525 526 527 528 -40-200 20406080100120 temperature (c) threshold (mv) vcc zener shunt voltage vs temperature 15.90 15.92 15.94 15.96 15.98 16.00 16.02 16.04 -40-200 20406080100120 temperature (c) zener shunt voltage (v)
14 ? 2006 semtech corp. www.semtech.com sc4911 power management outline drawing - msop-8 semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805)498-2111 fax (805)498-3804 contact information land pattern - msop-8 0 .010 .004 - .016 .003 .024 (.037) - .000 .030 - - - - 0.25 0.10 8 0 - 8 0.60 (.95) .032 .009 0.40 0.08 .043 .006 .037 0.75 0.00 - 0.80 0.23 - 0.95 1.10 0.15 - - - 3. dimensions "e1" and "d" do not include mold flash, protrusions or gate burrs. -b- controlling dimensions are in millimeters (angles in degrees). datums and to be determined at datum plane notes: 1. 2. -a- -h- side view a b c e h e/2 d plane detail .193 bsc .026 bsc aaa c seating ccc c 2x n/2 tips indicator e/2 pin 1 2x 8 bbb c a-b d see detail a1 a a2 bxn d 0.25 a plane gage .005 e1 12 n .114 .114 .118 .118 .009 - 8 01 c (l1) l a 0.13 3.00 3.00 4.90 bsc 0.65 bsc .122 .122 2.90 2.90 .015 0.22 3.10 3.10 0.38 - reference jedec std mo-187, variation aa. 4. dim ccc a1 e bbb aaa 01 l1 n l d e1 e a2 b c a millimeters nom dimensions inches min nom max min max e this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. p x (c) y z g .224 .063 .016 .026 (.161) .098 (4.10) 5.70 1.60 0.40 0.65 2.50 millimeters dimensions dim inches x z y c p g

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