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product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 1 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 features 384x series pin-to-pin compatible linearly decreasing pwm frequency burst-mode at low/zero load 5ua start-up current 5ma operating current vcc over voltage protection cycle-by-cycle current limiting zero cross-conduction slew rate controlled high current totem pole output fast current sense propagation delay under voltage lockout (uvlo) with hysteresis applications switching mode power supplies power converters description the sg348xg series of current-mode pwm controllers combines high performance with green-mode power saving features. sg348xg controllers are fully pin-to-pin compatible with bipolar uc384x devices, but they have improved features and functionality. sg384xg series controllers are compatible with the bicmos fabrication process, enabling the use of low start-up current and operating currents. this feature further improves power conversion efficiency. the minimal start-up current has been reduced to 5ua, and the minimum operating current has been reduced to 5ma. each sg384xg has a slew rate controlled high current totem pole output, ideally suited for driving a power mosfet while keeping emi low. the current-sense propagation delay is typically 50ns, resulting in significantly more effective constant power protection. during normal operation, a sg384xg controller acts as a fixed frequency pwm controller. the pwm frequency can be easily programmed by changing external r t and c t values. the sg384xg includes two green-mode functions that dramatically reduce power usage, helping the power supply comply with the latest international power saving guidelines. to cut power consumption under light load conditions, the controller?s green-mode function will linearly decrease the pwm frequency in response to decreases in the output load. under ultra light-load/zero-load conditions, the rt/ct pwm oscillator periodically shuts down, and enters into burst-mode. this causes the ic?s supply voltage to begin gradually dropping. just before the supply voltage drops below the uvlo voltage threshold, the rt/ct pwm oscillator turns back on, to prevent the supply voltage from going below the uvlo voltage. sg384xg controllers also come with over voltage protection (ovp). this shuts down pwm output if the supply voltage ever ex ceeds 27v. the sg 384xg series comes in 8-pin dip and sop packages. from auxiliary winding comp vref vfb o ut put s e nse g nd v c c sg384x r in 1.5m r41 100 r42 1k r s 0 .3 c25 100p c21 0.1u c t 3.3n rac 10k r t 10k from bridge rectifier 120~ 3 80vdc c in 10u oscillator frequency (fosc) vs comp voltage 0 10 20 30 40 50 60 1 1.5 2 2.5 3 comp voltage (v) fosc (khz) typical application green-mode operation oscillator frequency vs. comp
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 2 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 ordering information uvlo part number start threshold stop threshold maximum duty cycle package sg3842gad 8-pin dip sg3842gas 16v1v 10v1v 98% 8-pin sop sg3843gad 8-pin dip sg3843gas 8.9v0.5v 8.1v0.5v 98% 8-pin sop SG3844Gad 8-pin dip SG3844Gas 16v1v 10v1v 49% 8-pin sop sg3845gad 8-pin dip sg3845gas 8.9v0.5v 8.1v0.5v 49% 8-pin sop pin descriptions pin no. symbol function description 1 comp compensation output of the error amplifier and input to the pwm comparator. it is used for feedback loop compensation. 2 vfb feedback inverting input of the error amplifier. it is normally connected to the switching power supply output through a resistor divider. 3 sense current sense current sense comparator input. it is internally set to 1v maximum. a voltage proportional to the inductor current is connected to this input. 4 rt/ct oscillator control oscillator rc timing connection. connecting a resistor rt from this pin to vref, and a capacitor ct from this pin t o ground, programs the oscillator frequency and the maximum output duty cycle. 5 gnd ground this pin is the combined control circuit ground and power ground. 6 output output high-power, totem-pole driver output. this output drives the gate of a power mosfet. 7 vcc power supply supply voltage input. 8 vref reference voltage 5v-reference voltage output. marking information pin configuration 8 1 sg384 z g t a xxxxxxxyywwv z : 2, 3, 4, or 5 t : d = dip, s = sop xxxxxxx : wafer lot yy : year; ww : week v : assembly location rt/ct s ense vref vcc output gnd c omp v fb 3 1 2 5 6 8 7 4
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 3 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 block diagram _ + + _ _ + osc green mode controller clk q t-type s r q enb output internal bias vref enb vcc 5v sg3844 sg3845 only 4 3 2 rtct vfb sense 1 comp gnd 5 6 vcc 7 8 vref output comp r r vs (n-1)r r vh / vl 1v absolute maximum ratings symbol parameter test condition value unit vcc supply voltage low impedance source zener clamp 25 28 v iz zener current 10 ma v in fb/sense terminal input voltage fb, sense -0.3 to 5.5v v i sink error amplifier sink current 10 ma pd power dissipation at ta<50c dip sop 800 400 mw r j-a thermal resistance junction-air dip sop 82.5 141 c/w t j operating junction temperature - +150 c t a operating ambient temperature - -40 to 125 c tstg storage temperature range - -65 to +150 c t l lead temperature (soldering) 10 sec dip 20 sec sop 260 220 c esd capability, hbm model 3.0 kv esd capability, machine model 200 v
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 4 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 operating conditions symbol parameter min. max. unit vcc supply voltage - 20 v c t oscillation timing capacitor 0.47 10 nf r t oscillation timing resistor 2.0 100 k ? f osc oscillation frequency 10 500 khz t a operating ambient temperature -40 105 c electrical characteristics reference voltage section symbol parameter test condition min. typ. max. unit vref reference output voltage ta=25c, io=1ma 4.75 5.0 5.25 v line line regulation vcc=10 to 20v - 2 20 mv load load current regulation io=1ma to 20ma - 20 50 mv vtc temperature stability - - 0.5 - mv/c ios short-circuit output current - -30 -85 -180 ma vref total output variation line, load, temperature 4.75 5.0 5.25 v vn output noise voltage f=10hz to 10khz , ta=25c - 50 - uv s long term stability ta=125c for 1000 hours - 5 25 mv oscillator section (vfb=0v, sense=0v) symbol parameter test condition min. typ. max. unit sg3842g, sg3843g, sg3842g2, SG3844G2 49 52 55 khz fosc oscillator frequency SG3844G, sg3845g 24 26 28 khz f osc-g green-mode frequency (note 1) vsense=0v 8 12 16 khz sg3842g, SG3844G 2.60 v v comp,h comp voltage that initiates green-mode sg3842g2, sg3843g, SG3844G2, sg3845g 2.00 v sg3842g, SG3844G 1.40 v v comp,l comp voltage that shuts down pwm sg3842g2, sg3843g, SG3844G2, sg3845g 1.30 v fdv frequency change with vcc vcc=10 to 20v - 0.2 1 % fdt frequency change with temp. ta=-40 to 85c - 0.02 - %/c i dischg discharge current ta=25c 7 9 12 ma note 1: f osc-g is the last pwm frequency before completely turned off @ vcc=15v error amplifier section symbol parameter test condition min. typ. max. unit v fb input voltage comp=2.5v 2.45 2.5 2.55 v iib input bias current - - - 0.1 ua avol open-loop voltage gain - 45 55 - db bw unity gain bandwidth - 0.7 1.2 - mhz psrr power supply rejection ratio - 50 - - db isource output source current fb=2.3v,comp=0v -0.8 -1.8 -3 ma isink output sink current fb=2.7v,comp=1v 2 6.5 - ma v h comp output voltage fb=2.3v, r l =15k to gnd 6 6.6 - v v l comp output voltage fb=2.7v, r l =15k to vref - - 700 mv
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 5 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 current sense section symbol parameter test condition min. typ. max. unit sg3842g, SG3844G 4.60 5.00 5.40 v/v av current sense input voltage gain (n) sg3842g2, SG3844G2, sg3843g, sg3845g 2.76 3.00 3.24 v/v i ib input bias current - - -1 -5 ua t pd delay to output ta=25c - 50 150 ns v th(is) maximum input signal - 0.9 1.0 1.1 v output section symbol parameter test condition min. typ. max. unit vol output voltage low vcc=15v, io=20ma - - 0.5 v voh output voltage high vcc=15v, io=20ma 13 - - v tr rising time ta=25c, cl=1nf - 50 150 ns tf falling time ta=25c, cl=1nf - 50 150 ns under-voltage lockout section symbol parameter test condition min. typ. max. unit sg3842g, SG3844G 15 16 17 v v th(on) start threshold voltage sg3843g, sg3845g 8.4 8.9 9.4 v sg3842g, SG3844G 9 10 11 v v th(off) minimum operating voltage sg3843g, sg3845g 7.6 8.1 8.6 v pwm section symbol parameter test condition min. typ. max. unit sg3842g, sg3842g2, sg3843g 90 95 98 % dcy (max) maximum duty cycle SG3844G, SG3844G2, sg3845g 45 47 49 % dcy (min) minimum duty cycle fb=5v, comp=open - - 0 % total standby current section symbol parameter test condition min. typ. max. unit sg3842g, SG3844G vcc=15v - 5 15 ua i cc st start-up current sg3843g, sg3845g vcc=8v - 3 10 ua i cc op operating supply current fb=sense=0v, vdd=15v, cl=1000pf - 5.0 6.5 ma vz power supply zener voltage icc=10ma 25 28 - v v p power supply protection voltage 27 v
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 6 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 typical characteristics sg3842g start-up current (i cc,st ) vs temperature 1.0 1.5 2.0 2.5 3.0 3.5 4.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) i cc,st ( ua ) operating supply current (i cc,op ) vs temperature 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) i cc,op ( ma ) reference voltage (v ref ) vs temperature 4.80 4.85 4.90 4.95 5.00 5.05 5.10 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) v ref ( v ) error amp input voltage (v fb ) vs temperature 2.47 2.48 2.49 2.50 2.51 2.52 2.53 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) v fb ( v ) oscillator frequency (fosc) vs temperature 49.0 50.0 51.0 52.0 53.0 54.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) f osc ( khz ) maximum duty cycle (d max ) vs temperature 94.00 94.50 95.00 95.50 96.00 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) d max ( % ) vcc=14.0v vcc=15.0v vcc=15.0v vcc=15.0v vcc=15.0v vcc=15.0v
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 7 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 oscillator discharge current (i disch ) vs temperature 6.5 7.0 7.5 8.0 8.5 9.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) i disch ( ma ) start threshold voltage (v th ) vs temperature 14.00 14.50 15.00 15.50 16.00 16.50 17.00 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) v th ( v ) minimum operating voltage (vcc,min) vs temperature 9.0 9.2 9.4 9.6 9.8 10.0 10.2 10.4 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) vcc,min( v ) output voltage low @ 20ma (vol) vs temperature 0.000 0.050 0.100 0.150 0.200 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) vol( v ) output voltage high @ vcc=15v (voh) vs temperature 14.80 14.82 14.84 14.86 14.88 14.90 14.92 14.94 14.96 14.98 15.00 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) voh( v ) start-up current vs vcc supply voltage 0.0 1.0 2.0 3.0 4.0 0 2 4 6 8 10 12 14 16 vcc voltage (v) vcc current ( ua) vcc=15.0v vcc=15.0v t emperature=25
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 8 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 vcc current vs vcc supply voltage 0 1 2 3 4 5 6 0 3 6 9 12 15 18 21 24 27 vcc voltage (v) vcc current ( ma) fosc-g (green mode) vs vcc 0 10 20 30 40 50 9 1011121314 vcc voltage (v) fos c-g (khz) oscillator frequency (fosc) vs comp voltage 0 10 20 30 40 50 60 11.522.53 comp voltage (v) fosc (khz) temperature=25 temperature=25 comp=1.4v temperature=25 vcc=15v
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 9 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 sg3843g start-up current (i cc,st ) vs temperature 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) i cc,st (ua ) vcc=7.76v operating supply current (i cc, o p ) vs temperature 3.5 4.0 4.5 5.0 5.5 6.0 6.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) i cc,op (ma ) vcc=15.0v reference voltage (v ref ) vs temperature 4.75 4.80 4.85 4.90 4.95 5.00 5.05 5.10 5.15 5.20 5.25 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) v ref (v ) vcc=15.0v error amp input voltage (v fb ) vs temperature 2.47 2.48 2.49 2.50 2.51 2.52 2.53 -40-25-10 5 2035506580 95110125 temperature ( ) v fb (v) vcc=15.0v oscillator frequency (f osc ) vs temperature 45.0 47.0 49.0 51.0 53.0 55.0 57.0 59.0 61.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) f osc (khz) vcc=13.0v maximum duty cycle (d max ) vs temperature 94.00 94.50 95.00 95.50 96.00 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) d max (%) vcc=13.0v
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 10 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 oscill ator di scharge current (i disch ) vs temperature 6.5 7.0 7.5 8.0 8.5 9.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) i disch (ma) vcc=15.0v start threshold voltage (v th(on) ) vs temperature 8.20 8.30 8.40 8.50 8.60 8.70 8.80 8.90 9.00 9.10 9.20 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) v th(on) (v) mini mum operation voltage (v th(off) ) vs temperature 7.95 8.00 8.05 8.10 8.15 8.20 8.25 -40 -25 -10 5 20 35 50 65 80 95 110 125 temperature ( ) v th(off) (v) output voltage low @ 20ma (vol) vs temperature 0.00 0.05 0.10 0.15 0.20 -40 -25 -10 5 20 35 50 65 80 95 110 125 t emperature ( ) vol (v) output voltage high @ vcc=15v (voh) vs temperature 14.80 14.82 14.84 14.86 14.88 14.90 14.92 14.94 14.96 14.98 15.00 -40 -25 - 1 0 5 20 35 50 65 80 95 11 0 1 25 temperature ( ) voh (v) start-up current vs vcc supply voltage 0 1 2 3 4 5 6 7 012345678 vcc voltage (v) vcc current (ua) t emperature=25
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 11 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 start-up current vs vcc supply voltage 0 1 2 3 4 5 6 7 8 9 0 5 10 15 20 25 vcc volt age (v) vcc current (ma) t emperature=25 f osc-g (green-mode) vs vcc 0 5 10 15 20 25 30 7 8 9 10 11 12 13 14 vcc voltage (v) f osc-g (khz) comp=1.4v temperature=25 oscillator frequency (f osc ) vs comp voltage 0 10 20 30 40 50 60 11.522.53 comp voltage(v) f osc (k hz ) vcc=15v temperature=25
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 12 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 operation description sg384xg devices have many advantages over traditional 384x devices and are completely pin-to-pin compatible with them. the following descriptions highlight the advantages and the differences of the sg384xga designs. start-up current the required start-up current is typically only 5ua. this ultra-low start-up current allows designers to supply the start-up power required by the sg384xg using a high-resistance and a low-wattage start-up resistor. for example, an application using wide input range (100v ac ~240v ac ) ac-to-dc power adapter could work with a 1.5 m ? /0.25w resistor, and a 10uf/25v vcc hold-up capacitor. operating current the operating current has been reduced to 5.0ma. this low operating current results in higher efficiency and reduces the required vcc hold-up capacitance. oscillator operation the resistor r t and the capacitor c t , both connected to the pin rt/ct, determine the oscillation frequency. the capacitor c t is normally charged to 2.9v through the resistor r t, which is connected to a 5v reference voltage and discharged to 1.3v by a built-in constant current sink. the dead-time is generated during the discharge period. the SG3844G/45g both have an internal divide-by-two flip-flop driven by the oscillator, resulting in a 50% maximum duty cycle. thus, the output switching frequency is 1/2 of the oscillation frequency determined by r t and c t . () () [] f c k r khz f t t ? = 72 . 1 ) ( error amplifier the error amplifier?s inverting input is connected to the fb pin, and the output is connected to the comp pin. the comp output is available for external compensation, allowing designers to control the feedback-loop frequency-response. non-inverting input is not wired out to a pin, but it is internally biased to a fixed 2.5v 2% voltage. current sensing and pwm limiting the sg384xg current-sense input is designed for current-mode control. current-to-voltage conversion is done externally through the current-sense resistor rs. under normal operation, the comp voltage determines the peak-voltage across rs. v comp is the voltage at the pin comp and n is the current-sense input voltage gain. s comp pk r n v i ? = * 4 . 1 * n = is typically 5 (4.60 ~ 5.40) for the sg3842g and the SG3844G standard versions. n = 3 typically (2.76 ~ 3.24) for the sg3842g2 , SG3844G2 , sg3843g , and the sg3845g models. this feature is compatible with general 384x series products. a higher n value attenuates the feedback and ensures loop stability under light-load conditions. the inverting input to the sg384xg current-sense comparator is internally clamped to 1v. under voltage lockout (uvlo) the under voltage lockout (uvlo) function ensures the sg384xg?s supply voltage vcc will be sufficiently high before the output stage is enabled. the turn-on and turn-off threshold voltages are fixed internally at 16v/10v for the sg3842g/44g and at 8.9v/8.1v for the sg3843g/45g. the hysteresis voltage between turn-on and turn-off prevents vcc from being unstable during power on/off sequencing. at start-up, before the output
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 13 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 switch is enabled, the vcc hold-up capacitor c in must be charged up to 16v (sg3842g/44g) through the start-up resistor r in, the ultra-small start-up current of 5ua allows very large resistance values for the resistor r in to be used, even with low input voltages. for example, if v ac = 90vrms, r in can be as large as 1.5 m ? and still charge the hold-up capacitor c in . the power dissipation from this larger resistance r in would then be less than 70mw (0.07w), even under high line conditions (v ac = 240vrms). after the ic starts-up and begins normal operation, one of the transformer?s auxiliary windings generates the supply voltage vcc, which supplies the operating current of the sg384xg controller. slew rate controlled output driver the bicmos output stage directly drives the external power mosfet up to the full supply voltage. the output driver, with a low on-resistance and high current-driving capability, can easily drive an external capacitive load larger than 1000pf. if operating under recommended conditions, the switching frequency can go up to 500khz. the output stage is designed to ensure zero cross- conduction current. this minimizes heat dissipation, increases efficiency, and enhances reliability. the output driver is also slew-rate controlled to minimize emi. green-mode: linearly decreasing frequency and burst-mode system general?s patented green-mode function reduces the switching frequency under light-load and zero-load conditions. modulation of the pwm frequency can reduce power consumption under light-load and zero-load conditions, because the power loss is directly proportional to the switching frequency. most of the power loss in a power supply occurs due to the switching loss of the transistor, the core loss of the transformer and inductors, and the power loss of the snubber. these sources of power loss all lose power in proportion to the switching frequency. the controller uses the output of the error amplifier as a feedback voltage to calculate load conditions. when the feedback voltage goes below the green-mode threshold voltage, the switching frequency will be reduced. under normal-load and high-load conditions, the pwm operates as usual, and the frequency modulation feature does not affect its operation. there are two factors that determine the pwm frequency: 1. the resistor r t and the capacitor c t determine the rc charge and discharge times, and therefore, the circuit frequency. they are both connected to the pin rt/ct. 2. internal comparator threshold voltages. under normal-load conditions, the internal comparator threshold voltages are fixed at 1.3v (v comp,l ) and 2.9v (v comp,h ). under light-load conditions, the v comp,h internal threshold voltage gradually increases. this will increase the rc charging/discharging time, therefore decreasing the frequency. under ultra-light or zero-load conditions, the v comp,h voltage is increased to 4.6v. this will put the circuit into the lowest frequency it can operate at. assuming r t = 10k and c t = 3.3nf, this is about 12khz. the frequency vs. comp voltage (feedback from the output load) is shown in fig.1. fig.1 oscillator frequency vs. comp voltage if 12khz is not low enough to meet stand-by power conservation requirements, a shunt resistor r c can be connected in parallel with the capacitor c t between rt/ct and gnd. this will allow the sg384xg to enter into burst-mode. oscillator frequency (fosc) vs comp voltage 0 10 20 30 40 50 60 11.522.53 comp voltage (v) fosc (khz) temperature=25 vcc=15v
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 14 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 for example, assuming r t = 10k ? and r c = 47k ? , the peak rt/ct voltage would only be: () v v 12 . 4 47 10 47 5 = + since 4.12v is less than the internal v comp,h 4.6v voltage under light-load conditions, the rt/ct oscillator would take a long time to charge up to 4.6v. in this situation, the rt/ct oscillator will stop oscillating. when oscillation stops, there is no pwm output. consequently, the energy required to supply the sg384xg from the auxiliary winding also gets cut off. this causes the supply voltage vcc to start dropping. if the supply voltage vcc drops below the uvlo voltage, it will take the sg384xg several hundred milliseconds to start-up. this delay will cause too much fluctuation to the output voltage. to avoid this, the sg384xg will automatically reduce the internal v comp,h voltage, turning the rt/ct oscillator back on when the vcc supply voltage falls within 1.5v of the uvlo voltage. in burst-mode, the pwm frequency is burst between 0hz and the light-load tens of khz region, not over the full frequency range. fig.2 shows the green-mode frequency vs. the supply voltage vcc. the green-mode frequency is fixed at 12khz when vcc is above 11v. when vcc is below 11v and approaching uvlo, the pwm frequency is gradually increased. this increases the energy supplied to vcc, and pulls up the vcc supply voltage to prevent it from dropping below uvlo. these techniques help achieve optimal power savings. the sg384xg can linearly decrease the pwm frequency under light-load conditions, and enter into burst-mode under ultra-light load and zero-load conditions. linear frequency reduction and burst-mode enable the sg384xg to deliver excellent power savings and load regulation. fosc-g (green mode) vs vcc 0 10 20 30 40 50 9 1011121314 vcc voltage (v) fos c-g (khz) vcc over voltage protection (ovp) when the sg384xg?s supply voltage increases to 27v due to abnormal conditions, such as an open loop from the photo-coupler, or a short circuit on the output side, the sg384xg will stop pwm output, to protect the entire power supply from being damaged. noise immunity noise from the current-sense or the control signal can cause significant pulse-width jitter, particularly under continuous-mode operation. slope compensation partially alleviates this problem, but the designer should be aware of its presence. the 384x has a single ground pin. high sink current in the output therefore cannot be returned separately. ceramic bypass capacitors (0.1uf) from vcc and vref to ground will provide low-impedance paths for high-frequency transients. for best results, good high-frequency and rf layout practices should be followed. the designer should avoid long pcb traces and component leads. the oscillator, compensation, and filter components should be located near the 384x. in order to minimize noise interference to the oscillator, it is recommended that c t should never be less than 1000pf. noise caused by the output (pin 6) also causes problems sometimes. this is because the pin is being pulled below ground at turn-off by the external parasitic. this is comp=1.4v temperature=25 d rop below uvlo fig.2 green-mode frequency vs. supply voltage vcc
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 15 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 particularly true when driving a mosfet. a resistor series connected from the output (pin 6) to the gate of the mosfet will prevent such output noise.
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 16 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 reference circuit universal input, 12v/5a dc output bom symbol components symbol components bd1 bd 1a/600v r1,3 470k 1/4w c1 r2 c2 ec 68u/400v r4 1m 1/4w c3 cc 102p/1kv r5 43 1/2w c4 yc 222p r6 4.7k 1/4w c5 ec 1200u/16v r13 0.5 1w c6 ec 680u/16v r14 10 1/8w c12 ec 10u/25v r17 100 1/8w d1 led tr2 sck054 d2 t1 ei28 d3 zd 15v u1 sg384xg d4 1n4148 u2 4n35d f1 2a/250v u3 tl431 l1 uu10.5 vz1 vz l2 xc1 xc 0.22u q2 mos 2a/600v vo + vi n vr vb vb vo + vr xc 1 vz1 1 2 p1 r3 r1 + c6 bd1 2 1 3 4 + c2 r6 f1 + c12 d3 2 1 d1 2 1 q2 1 2 3 c4 u1 sg3842g 3 5 6 7 2 1 8 4 is gnd o/p vcc fb com vre r/c r13 r8 r10 c8 c11 r16 c10 r12 c7 r4 r2 p2 l2 1 2 r9 r11 r17 r19 r20 c13 r18 u3 3 1 2 u2 1 2 3 4 tr2 1 2 l 1 2 3 4 r7 d4 2 1 d2 2 1 1,2 3 4 5 6,7 8,9 1,2 3 4 56,7 8,9 + c5 q1 1 3 2 c3 r5 c1 c01 r14 d5 do7 2 1
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 17 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 package information 8 dip outline dimensions 4 1 85 d e1 e e b a1 a2 a b b1 l e dimensions millimeter inch 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 bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 18 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 8 sop outline dimensions 1 4 85 h e e b a a1 d c f l dimensions millimeter inch symbol min. typ. max. min. typ. max. a 1.346 1.752 0.053 0.069 a1 0.101 0.254 0.004 0.010 b 0.406 0.016 c 0.203 0.008 d 4.648 4.978 0.183 0.196 e 0.381 3.987 0.150 0.157 e 1.270 0.050 f 0.381x45 ? ?? ? ? ?? ? ? ?? ? 0 ? ?? ? 8 ? ?? ? 0 ? ?? ? 8 ? ?? ?
product specification bicmos green-mode pwm controllers sg3842g/ 3843g/ 3844g/ 3845g ? system general corp. - 19 - www.sg.com.tw version d.2 ( iro33.0007.b1) apr.22,2003 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 in other applications in which failure of the 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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