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product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 1 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 features ? green-mode pwm ? supports the ?blue angel? standard ? low start-up current (10a) ? low operating current (2.5ma) ? leading-edge blanking ? constant output power limit ? universal input ? built-in synchronized slope compensation ? current-mode operation ? cycle-by-cycle current limiting ? under voltage lockout (uvlo) ? programmable pwm frequency ? v dd over-voltage protection (auto restart) ? gate output voltage clamped at 17v ? low cost ? few external components required ? small sot-26 and dip-8 packages applications general-purpose, switching-mode power supplies and flyback power converters, such as: ? battery chargers for cellular phones, cordless phones, pdas, digital cameras, and power tools ? power adapters for ink jet printers, video game consoles, and portable audio players ? open-frame smps for tv/dvd standby and auxiliary supplies, home appliances, and consumer electronics ? replacements for linear transformers and rcc smps ? pc 5v standby power description this highly integrated pwm controller provides several special enhancements designed to meet the low standby power needs of low-power smps. to minimize standby power consumption, the proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency under light-load conditions. this green-mode function enables the power supply to meet even the strictest power conservation requirements. the bicmos fabrication process enables reducing the start-up current to 10a and the operating current to 2.5ma. to further improve power conservation, a large start-up resistance can be used. built-in synchronized slope compensation ensures the stability of peak current mode control. proprietary internal compensation provides a constant output power limit over a universal ac input range (90v ac to 264v ac ). pulse-by-pulse current limiting ensures safe operation even during short-circuits. to protect the external power mosfet from being damaged by supply over-voltage events, the sg6858?s output driver is clamped at 17v. sg6858 controllers can be used to improve the performance and reduce the production cost of power supplies and can replace linear and rcc-mode power adapters. it is available in 8-pin dip and 6-pin sot-26 packages. typical application
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 2 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 marking diagrams pin configuration ordering information part number pb-free package sg6858tz 6-pin sot-26 SG6858DZ 8-pin dip-8 pin descriptions pin no. name dip-8 sot-26 type function gate 1 6 driver output the totem-pole output driver for driving the power mosfet. vdd 2 5 supply power supply. nc 3 no connection nc pin. sense 4 4 analog input current sense. this pin senses the voltage across a resistor. when the voltage reaches the internal threshold, pwm output is disabled. this activates over-current protection. this pin also provides current amplitude information for current-mode control. ri 5 3 analog input/output a resistor connected from the ri pin to ground generates a constant current source used to charge an internal capacitor and determines the switching frequency. increasing the resistance reduces the amplitude of the current source and reduce the switching frequency. a 95k ? resistor, r i , results in a 50a constant current i i and a 70khz switching frequency. nc 6 no connection nc pin. fb 7 2 analog input feedback. the fb pin provides the output voltage regulation signal. it provides feedback to the internal pwm comparator, so that the pwm comparator can control the duty cycle. gnd 8 1 supply ground. aai: sg6858 m : mask version w : week code a~z=w1~w26 a ~z =w27~w52 : lead free package sot-26 gnd fb ri gate vdd sense d : d=dip p: z=lead free null=regular package xxxxxxxx : wafer lot y : year; ww : week v : assembly location dip-8 ri nc fb gnd sense n c vdd gate aaimw xxxxxxxxywwv sg6858dp
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 3 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 block diagram
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 4 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 absolute maximum ratings symbol parameter value unit v vdd dc supply voltage* 30 v v fb input voltage to fb pin -0.3 to 7.0 v v sense input voltage to sense pin -0.3 to 7.0 v t j operating junction temperature -40 to +125 c sot 208.4 c/w r ja thermal resistance (junction-to-air) dip 82.5 c/w t stg storage temperature range -55 to +150 c t l lead temperature (wave soldering or infrared, 10 seconds) 260 c v esd-hbm electrostatic discharge capability, human body model 3.0 kv v esd-mm electrostatic discharge capability, machine model 200 v * all voltage values, except differential voltages, are given with respect to gnd pin. * stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. recommended operating conditions symbol parameter value unit v dd dc supply voltage Q 22 v t a operating ambient temperature -20 to +85 c * for proper operation. electrical characteristics v dd =15v, t a = 25 c, unless otherwise noted. v dd section symbol parameter test condition min. typ. max. unit v dd-op continuously operation voltage 22 v v dd-on turn-on threshold voltage 15.5 16.5 17.5 v v dd-off turn-off threshold voltage 10.5 11.5 12.5 v i dd-st start-up current v dd =v dd-on ? 0.1v 10 15 a i dd-op operating supply current v dd =15v, gate with 1nf to gnd 2.5 3.5 ma v dd-ovp v dd over-voltage protection level 24 25 26 v t d-vddovp v dd over-voltage protection debounce 50 125 200 s v dd-g off v dd low threshold voltage to exit green-off mode v dd-off + 0.95 v dd-off + 1.10 v dd-off + 1.25 v
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 5 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 feedback input section symbol parameter test condition min. typ. max. unit a v fb input to current comparator attenuation 2/5 v/v z fb input impedance 5 k ? v fb-open fb output high voltage 4.5 5.0 5.5 v v fb-n green-mode entry fb voltage 2.85 v v fb-g green-mode ending fb voltage 2.20 v s g green-mode modulation slope r i =95k ? 75 hz/mv current-sense section symbol parameter test condition min. typ. max. unit z sense input impedance 10 k ? t pd delay to output 60 100 ns v sthfl flat threshold voltage for current limit 0.96 v v sthva valley threshold voltage for current limit 0.75 0.80 0.85 v t leb leading-edge blanking time 250 300 350 ns dcy saw duty cycle of saw limit max. duty cycle 45 % oscillator section symbol parameter test condition min. typ. max. unit f osc frequency r i =95k ? 65 70 75 khz f osc-g green-mode frequency r i =95k ? 22 khz f dv frequency variation vs. v dd deviation v dd =13.5v to 22v 0 0.02 2.00 % f dt frequency variation vs. temperature deviation t a = -20 to 85 c 2 % output section symbol parameter test condition min. typ. max. unit dcy max maximum duty cycle 70 75 80 % v gate-l output voltage low v dd =15v, i o =20ma 1.5 v v gate-h output voltage high v dd =13.5v, i o =-20ma 8 v t r rising time v dd =15v, c l =1nf 150 200 250 ns t f falling time v dd =15v, c l =1nf 35 55 75 ns v gate-clamp output clamp voltage v dd =22v 16 17 18 v
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 6 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 typical characteristics turn-on threashold voltage (v dd-on ) vs temperature 15.5 16.0 16.5 17.0 17.5 -40-25-10 5 203550658095110125 temperature () v dd-on (v) turn-off threshold voltage (v dd-off ) vs temperature 10.5 10.9 11.3 11.7 12.1 12.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature () v dd-off (v) startup current(i dd-st ) vs temperature 0 5 10 15 20 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature () i dd-st (ua) operating supply current (i dd-op ) vs temperature 1.5 2.0 2.5 3.0 3.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature () i dd-op (ma) frequency (f osc ) vs temperature 65 67 69 71 73 75 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature () f osc (khz) maximum duty cycle (dcy max ) vs temperature 70 72 74 76 78 80 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature () dcy ma x (%) v dd =15v v dd =15v v dd =15v v dd =15v
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 7 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 green-mode entry fb voltage(v fb-n ) vs temperature 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature () v fb-n (v) green-mode ending fb voltage (v fb-g ) vs temperature 1.90 2.00 2.10 2.20 2.30 2.40 2.50 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature () v fb-g (v) leading-edge blanking time (t leb ) vs temperature 250 270 290 310 330 350 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature () t leb (nsec) operation current (i dd-op ) vs vdd voltage 1.5 2.0 2.5 3.0 3.5 12 13 14 15 16 17 18 19 20 21 22 23 24 vdd voltage (v) i dd-op (ma) v dd =15v v dd =15v v dd =15v
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 8 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 operation description sg6858 devices integrate many useful designs into one controller for low-power switch-mode power supplies. the following descriptions highlight some of the features of the sg6858 series. start-up current the start-up current is only 10a, which allows a start-up resistor with a high resistance and a low-wattage to supply the start-up power for the controller. a 1.5m ? , 0.25w, start-up resistor and a 10f/25v v dd hold-up capacitor are sufficient for an ac-to-dc power adapter with a wide input range (100v ac to 240v ac ). operating current the operating current has been reduced to 2.5ma. the low operating current results in higher efficiency and reduces the v dd hold-up capacitance requirement. green-mode operation the proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency under light-load conditions. on-time is limited to provide stronger protection against brownouts and other abnormal conditions. the feedback current, which is sampled from the voltage feedback loop, is taken as the reference. once the feedback current exceeds the threshold current, the switching frequency starts to decrease. this green-mode function dramatically reduces power consumption under light-load and zero-load conditions. power supplies using the sg6858 can meet even the strictest regulations regarding standby power consumption. oscillator operation a resistor connected from the ri pin to ground generates a constant current source used to charge an internal capacitor. the charge-time determines the internal clock speed and the switching frequency. increasing the resistance reduces the amplitude of the input current and the switching frequency. a 95k ? resistor, r i , results in a 50a constant current, i i , and a 70khz switching frequency. the relationship between r i and the switching frequency is: ) ( khz ) (k r 6650 i pwm f = (1) leading-edge blanking each time the power mosfet is switched on, a turn-on spike occurs at the sense-resistor. to avoid premature termination of the switching pulse, a 300ns leading-edge blanking time is built in. conventional rc filtering can therefore be omitted. during this blanking period, the current-limit comparator is disabled and cannot switch off the gate driver. constant output power limit when the sense voltage across the sense resistor, r s , reaches the threshold voltage (around 0.96v), the output gate drive is turned off following a short propagation delay t pd . this propagation delay introduces additional current proportional to t pd ?v in /l p . the propagation delay is nearly constant regardless of the input line voltage v in . higher input line voltages result in larger additional currents. at high input line voltages, the output power limit is higher than at low input line voltages. to compensate for this output power limit variation across a wide ac input range, the threshold voltage is adjusted by adding a positive ramp (v limit_ramp ). this ramp signal rises from 0.80v to 0.96v, then flattens out at 0.96v. a smaller threshold voltage forces the output gate drive to terminate earlier. this reduces the total pwm turn-on time and makes the output power equal to that of low line input. this proprietary internal compensation ensures a constant output power limit for a wide ac input voltage range (90v ac to 264v ac ).
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 9 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 under-voltage lockout (uvlo) the turn-on and turn-off thresholds of the sg6858 are fixed internally at 16.5v/11.5v. during start-up, the hold-up capacitor must be charged to 16.5v through the start-up resistor to enable sg6858. the hold-up capacitor continues to supply v dd until power can be delivered from the auxiliary winding of the main transformer. v dd must not drop below 11.5v during this start-up process. this uvlo hysteresis window ensures that hold-up capacitor is adequate to supply v dd during start-up. v dd over-voltage protection v dd over-voltage protection has been built in to prevent damage due to over-voltage conditions. when the voltage v dd exceeds the internal threshold due to abnormal conditions, pwm output is turned off until the v dd voltage drops below the uvlo, then starts up again. over-voltage conditions are usually caused by open-feedback loops. gate output the bicmos output stage is a fast totem pole gate driver. cross conduction has been avoided to minimize heat dissipation, increase efficiency, and enhance reliability. the output driver is clamped by an internal 17v zener diode to protect power mosfet transistors against undesired over-voltage gate signals. built-in slope compensation the sensed voltage across the current sense resistor is used for current-mode control and pulse-by-pulse current limiting. built-in slope compensation improves stability and prevents sub-harmonic oscillations due to peak-current mode control. the sg6858 has a synchronized, positively-sloped ramp built-in at each switching cycle. the slope of the ramp is: .) (max duty duty 36 . 0 (2) noise immunity noise from the current sense or the control signal can cause significant pulse width jitter, particularly in continuous-conduction mode. while slope compensation helps alleviate these problems, further precautions should still be taken. good placement and layout practices should be followed. avoiding long pcb traces and component leads, locating compensation and filter components near the sg6858, and increasing the power mos gate resistance improves performance.
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 10 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 reference circuit bom reference component reference component bd1 bd 1a/500v l2 inductor 10h 6mm cx1 (optional) xc 0.1f q1 mosfet 1a/600v cy1 (optional) yc 1000pf/400v (y1) r1,r2 r 750k ? 1206 c1 cc 10nf/500v r4,r3 r 47k ? 1206 c2 ec 10f/400v 105 r5 r 47 ? 1206 c3 cc 1000pf/500v r6 r 4.7 ? 1206 c4 ec 10f/50v r7 r 100 ? 0805 c6 cc 1000pf 0805 r8 r 10 ? 1206 c7 (optional) cc 1000pf/100v 1206 r9 r 100k ? 0805 c8 ec 470f/10v 105 r10 (optional) r 10 ? 1206 c9 ec 220f/10v 105 r11 r 100 ? 1/8w c10 cc 2200pf 0805 r12 r 33k ? 0805 c11 n.c. r13 r 33k ? 1/8w d1 diode fri07 r14 r 4.7k ? 0805 d2 diode fr102 r15 r 0 ? 0805 d4 diode sb360 t1 transformer ee-16 d5 (optional) zd 6.8v 0.5w u1 ic sg6858 f1 r 1 ? /0.5w u2 ic pc817 l1 inductor 20mh 6x8mm u3 ic tl431 f1 r7 r6 r3 r1 r5 r4 r9 r10 r11 r13 r12 r14 r8 r2 c3 c7 cy1 c10 c1 cx1 c2 c9 c4 c8 c6 1 2 l1 10 5 7 3,4 1,2 8 9 t1 2 1 d1 1 2 3 q1 gnd 1 fb 2 ri 3 sense 4 vdd 5 gate 6 u1 2 1 d2 1 2 3 4 u2 2 1 d4 2 1 d5 1 2 l2 2 3 1 u3 1 4 3 2 bd1 vo gnd l n r15 c11
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 11 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 package information 8 pins - dip (d) 4 1 8 5 d e1 e e b a1 a2 a b b1 l e x dimensions millimeters inches symbol min. typ. max. min. typ. max. a 5.334 0.210 a1 0.381 0.015 a2 3.175 3.302 3.429 0.125 0.130 0.135 b 1.524 0.060 b1 0.457 0.018 d 9.017 9.271 10.160 0.355 0.365 0.400 e 7.620 0.300 e1 6.223 6.350 6.477 0.245 0.250 0.255 e 2.540 0.100 l 2.921 3.302 3.810 0.115 0.130 0.150 e b 8.509 9.017 9.525 0.335 0.355 0.375 ? 0 ? 7 ? 15 ? 0 ? 7 ? 15 ?
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 12 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007 6 pins - sot (t) 1 3 6 4 e e1 e1 e d b a2 a1 a r 1 r l2 l1 l detail a detail a c 1 1 dimensions millimeters inches symbol min. typ. max. min. typ. max. a 1.45 0.057 a1 0.15 0.006 a2 0.90 1.15 1.30 0.036 0.045 0.051 b 0.30 0.50 0.011 0.020 c 0.08 0.22 0.003 0.009 d 2.90 0.114 e 2.80 0.110 e1 1.60 0.063 e 0.95 0.037 e1 1.90 0.075 l 0.30 0.45 0.60 0.020 0.018 0.024 l1 0.60 0.024 l2 0.25 0.010 r 0.10 0.004 r1 0.10 0.25 0.004 0.010 ? 0 4 8 0 4 8 1 5 10 15 5 10 15
product specification low-cost, green-mode pwm controller for flyback converters sg6858 ? system general corp. - 13 - www.sg.com.tw ? www.fairchildsemi.com version 1.2.1 (iao33.0045.b2) september 25, 2007

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