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product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 1 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 features green-mode pwm supports the ?blue angel? standard low start-up current (5ua) low operating current (2ma) 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 gate output voltage clamped at 15v low cost few external components required small sot-26 package 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 other 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 easily meet even the strictest power conservation requirements. the bicmos fabrication process enables reducing the start-up current to 5ua, and the operating current to 2ma. 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 (90vac to 264vac). 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, the sg6848?s output driver is clamped at 15v. sg6848 controllers can be used to improve the performance and reduce the production cost of power supplies. the sg6848 is the best choice for replacing linear and rcc-mode power adapters. it is available in 8-pin dip and 6-pin sot-26 packages. typical application from auxiliary winding fb o u tp u t sense r i gnd vdd sg6848 r in 1.5m r7 100 r s 4.7 c6 472p r9 95k from bridge rectifier 120~ 380vdc c in 10u
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 2 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 marking diagrams pin configuration ordering information part number pwm frequency package sg6848t 70khz 6-pin sot-26 sg6848d 70khz 8-pin dip-8 sg6848tz 70khz 6-pin sot-26 (lead free) SG6848DZ 70khz 8-pin dip-8 (lead free) 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 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 will generate a constant current source for the sg6848. this current is used to charge an internal capacitor, to determine the switching frequency. increasing the resistance will reduce the amplitude of the current source and reduce the switching frequency. a 95k ? resistor r i results in a 50ua constant current i i and a 70khz switching frequency. nc 6 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. m : mask version x: a=sg6848 d=sg6848 (lead free) y : year; ww : work week 1 2 3 4 5 6 sot-26 gnd fb ri gate vdd sense 1 mxyw w d : d=dip p : z =lead free null=regular package xxxxxxx : wafer lot yy : year; ww : week v : assembly location 8 1 sg6848dp xxxxxxxyywwv dip-8 ri nc fb gnd sense nc vdd gate 4 3 2 1 5 6 7 8
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 3 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 block diagram v dd 2 (5) ri uvlo 16.3v/11.7v internal bias _ + osc 5 (3) r q s ocp comp pwm comp slope compensation vlimit ramp green mode controller on/off driver 7 (2) 4.8v fb 1 (6) v dd sense 4 (4) gate blanking circuit 8 (1) gnd
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 4 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 absolute maximum ratings symbol parameter value unit v dd dc supply voltage * zener clamp zener current 25 26 10 v v ma v fb input voltage to fb pin -0.3 to 6 v v v sence input voltage to sense pin -0.3 to 6v v p d power dissipation 300 mw t j operating junction temperature 150 sot-26 208.4 c/w r ja thermal resistance (junction to air) dip-8 82.5 c/w t stg storage temperature range -55 to +150 t l lead temperature (soldering) 20 sec sot-26 10 sec dip-8 220 260 c esd capability, hbm model 3.0 kv esd capability, machine model 300 v * all voltage values, except differential voltages, are given with respect to the network ground terminal. operating conditions symbol parameter value unit v dd dc supply voltage Q 20 v t a operating ambient temperature -30 to +105 electrical characteristics (t a = 25 c , v dd =15v) feedback input section symbol parameter test condition min. typ. max. unit i oz zero duty cycle input current 1.3 2.0 ma v op open loop voltage 4.5 v current sense section symbol parameter test condition min. typ. max. unit z cs input impedance 10 k ? t pd delay to output 150 200 nsec v th,flt current limit flatten threshold voltage 1.0 v v th,valley current limit valley threshold voltage 0.80 0.85 0.90 v
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 5 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 oscillator section symbol parameter test condition min. typ. max. unit f osc frequency r i =95k ? 65 70 75 khz f osc-green green-mode frequency r i =95k ? 13 15 khz i g green-mode fb input current 1.16 ma i n green-mode start threshold fb input current i n = 0.3ma for a maximum duty cycle 1 ma s g green-mode modulation slope r i =95k ? 300 hz/ua f dy frequency variation versus v dd deviation v dd =12 to 20v 0.02 2 % f dt frequency variation versus temp. deviation t a =-30 to 105 2 % pwm section symbol parameter test condition min. typ. max. unit dc (max) maximum duty cycle 70 75 80 % dc (min) minimum duty cycle - 1 2 % b nk leading-edge blanking time 250 nsec output section symbol parameter test condition min. typ. max. unit v ol output voltage low v dd =15v, i o =20ma 1.5 v v oh output voltage high v dd =15v, i o =20ma 8 v t r rising time v dd =15v, c l =1nf 50 200 nsec t f falling time v dd =15v, c l =1nf 30 150 nsec v clamp output clamp voltage v dd =20v 15 17 v under voltage lockout section symbol parameter test condition min. typ. max. unit v th(on) start threshold voltage t a =25 c 15.3 16.3 17.3 v v dd(min) min. operating voltage t a =25 c 10.9 11.7 12.5 v total standby current section symbol parameter test condition min. typ. max. unit i dd st start-up current v dd =15v 5 30 ua i dd op operating supply current v dd =15v 2 5 ma
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 6 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 typical characteristics start-up threshold voltage (v th(on) ) vs temperature 14.5 15.0 15.5 16.0 16.5 17.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) v th(on) (v) min. operating voltage (v dd (min) ) vs temperature 10.6 10.8 11.0 11.2 11.4 11.6 11.8 12.0 12.2 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) v dd (min) (v) start-up crrent (i dd st ) vs tem perature 0 5 10 15 20 25 30 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) i dd st (ua) pwm oscillator frequency (f osc ) vs temperature 65.0 66.5 68.0 69.5 71.0 72.5 74.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) f osc (khz) frequency in green mode (f osc-green ) vs temperature 8 9 10 11 12 13 14 15 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) f osc-green (khz) max. duty cycle (dc (max) ) vs temperature 70 71 72 73 74 75 76 77 78 79 80 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) dc (max) (%)
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 7 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 pwm oscillator frequency (fosc) vs. fb 0 10 20 30 40 50 60 70 80 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 fb (ma) f osc (khz)
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 8 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 operation description sg6848 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 sg6848 series. start-up current the start-up current is only 5ua. low start-up current allows a start-up resistor with a high resistance and a low-wattage to supply the start-up power for the controller. a 1.5 m ? , 0.25w, start-up resistor and a 10uf/25v v dd hold-up capacitor would be 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 2ma. the low operating current results in higher efficiency and reduces the v cc 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 sg6848 can easily meet even the strictest regulations regarding standby power consumption. oscillator operation a resistor connected from the ri pin to ground will generate a constant current source for the sg6848. this current is used to charge an internal capacitor. the charge-time determines the internal clock speed and the switching frequency. increasing the resistance will reduce the amplitude of the input current and reduce the switching frequency. a 95k ? resistor r i results in a 50ua 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 ? = the range of the oscillation frequency is designed to be within 50khz ~ 100khz. leading-edge blanking each time the power mosfet is switched on, a turn-on spike will inevitably occur at the sense-resistor. to avoid premature termination of the switching pulse, a 250 nsec 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 it 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 1.0v), the output gate drive will be turned off following a short propagation delay t d . this propagation delay will introduce an additional current proportional to t d *v in /l p . the propagation delay is nearly constant regardless of the input line voltage v in . higher input line voltages will result in larger additional currents. at high input line voltages, the output power limit will be 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. this ramp signal rises from 0.85v to 1.0v, and then flattens out at 1.0v. 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 (90vac to 264vac).
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 9 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 under voltage lockout (uvlo) the turn-on and turn-off thresholds of the sg6848 are fixed internally at 16.3v/11.7v. during start-up, the hold-up capacitor must be charged to 16.3v through the start-up resistor, so that the sg6848 will be enabled. the hold-up capacitor will continue to supply v dd until power can be delivered from the auxiliary winding of the main transformer. v dd must not drop below 11.7v during this start-up process. this uvlo hysteresis window ensures that hold-up capacitor will be adequate to supply v dd during start-up. gate output the sg6848 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 15v zener diode in order 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 will improve stability and prevent sub-harmonic oscillations due to peak-current mode control. the sg6848 has a synchronized, positively-sloped ramp built-in at each switching cycle. the slope of the ramp is: (max) 33 . 0 duty duty 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 sg6848, and increasing the power mos gate resistance is advised.
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 10 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 reference circuit circuit vo gnd r13 c10 r12 + c9 u3 3 1 2 r1 d5 2 1 d1 2 1 r8 q1 1 2 3 c3 u1 1 2 3 4 5 6 gnd fb ri sense vdd gate + c2 f1 l1 1 2 d4 2 1 r11 c1 r4 u2 1 2 4 3 cx1 r7 -+ bd1 1 4 3 2 r5 t1 8 5 7 3,4 1,2 10 9 l2 1 2 c6 r9 + c4 r10 r6 r3 d2 2 1 + c8 cy1 c7 r14 r2 l n bom reference component reference component bd1 bd 1a/500v l2 10uh 6mm cx1 (optional ) yc 472p/400v (y1) q1 mosfet 1a/600v cy1 (optional ) yc 102p/400v (y1) r1,r2 r 750k ? 1206 c2 ec 10uf/400v 105 r4,r3 r 47k ? 1206 c1 cc 103p/500v r5 r 47 ? 1206 c3 cc 1000p/500v r6 r 4.7 ? 1206 c4 ec 10u/50v r7 r 100 ? 0805 c6 cc 472p 0805 r8 r 10 ? 1206 c7 (optional ) cc 102p/100v 1206 r10 (optional) r 10 ? 1206 c8 ec 470u/10v 105 r9 r 100k ? 0805 c9 ec 220u/10v 105 r11 r 100 ? 1/8w c10 cc 222p 0805 r12 r 33k ? 0805 d1 diode fri07 r13 r 33k ? 1/8w d2 diode fr102 r14 r 4.7k ? 0805 d4 diode sb360 t1 ee-16 d5 (optional ) zd 6.8v 0.5w u1 ic sg6848 (green pwm ic) f1 r 1 ? /0.5w u2 pc817 l1 20mh 6*8mm u3 tl431
product specification low cost green-mode pwm controller for flyback converters sg6848 ? system general corp. - 11 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 package information 8 pins -- dip (d) 4 1 85 d e1 e e b a1 a2 a b b1 l e 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 sg6848 ? system general corp. - 12 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 sot-26 (s) 1 3 64 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 sg6848 ? system general corp. - 13 - www.sg.com.tw version 1.4(iro33.0010.b2) apr.08, 2004 disclaimers life support system general?s products are not designed to be used as components in devices intended to support or sustain human life. use of system general?s products in components intended for surgical implant into the body, or other applications in which failure of system general?s products could create a situation where personal death or injury may occur, is not authorized without the express written approval of system general?s chief executive officer. system general will not be held liable for any damages or claims resulting from the use of its products in medical applications. military system general's products are not designed for use in military applications. use of system general?s products in military applications is not authorized without the express written approval of system general?s chief executive officer. system general will not be held liable for any damages or claims resulting from the use of its products in military applications. right to make changes system general reserves the right to change this document and/or this product without notice. customers are advised to consult their system general sales representative before ordering.

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