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p roduction d ata s heet t he i nfinite p ower of i nnovation l in f inity m icroelectronics i nc . 11861 w estern a venue , g arden g rove , ca. 92841, 714-898-8121, f ax : 714-893-2570 1 copyright ? 2000 rev. 1.6c,2006-02-02 sg1844/sg1845 series c urrent m ode pwm c ontroller description the sg1844/45 family of control ics provides all the neces sary features to implement off-line fixed frequency, current- mode switching power supplies with a minimum number of external components. current-mode architecture demonstrates improved line regulation, improved load regulation, pulse-by pulse current limiting and inherent protection of the power supply output switch. the bandgap reference is trimmed to 1% over temperature. oscillator discharge current is trimmed to less than 10%. the sg1844/45 has undervoltage lockout, current-limiting circuitry and start-up current of less than 1ma. the totem-pole output is optimized to drive the gate of a power mosfet. the output is low in the off state to provi de direct interface to an n-channel device. bo th operate up to a maximum duty cycle range of zero to <50% due to an internal toggle flip-flop which blanks the output off every other clock cycle. the sg1844/45 is specified for operation over the full military ambient temperature range of -55c to 125c. the sg2844/45 is specified for the industrial range of -25c to 85c, and the sg3844/45 is designed for the co mmercial range of 0c to 70c. important: for the most current data, consult microsemi ?s website: http://www.microsemi.com product highlight ac input sg3844 r st i st v cc key features ? optimized for off-line control ? low start-up current (<1ma) ? automatic feed forward compensation ? trimmed oscillator discharge current ? pulse-by-pulse current limiting ? enhanced load response ? characteristics ? under-voltage lockout with 6v hysteresis (sg1844 only) ? double pulse suppression ? high-current totem-pole output ? internally trimmed bandgap reference ? 500khz operation ? undervoltage lockout sg1844 - 16 volts sg1845 - 8.4 volts ? low shoot-through current <75ma over temperature high reliability features ? available to mil-std-883b ? linfinity level "s" processing available package order info m plastic dip 8-pin n plastic dip 14-pin dm plastic soic 8-pin d plastic soic 14-pin y ceramic dip 8-pin j ceramic dip 14-pin f cer flatpack 10-pin l ceramic lcc 20-pin t a ( c) rohs compliant / pb-free transition dc: 0503 rohs compliant / pb-free transition dc:0440 sg3844m sg3844n sg3844dm sg3844d sg3844y sg3844j 0 to 70 sg3845m sg3845n sg3845dm sg3845d sg3845y sg3845j sg2844m sg28424n sg2844dm sg2842d sg2844y sg2844j -25 to 85 sg2845m sg2845n sg2845dm sg2845d sg2845y sg2845j sg1844y sg1844j sg1844l -55 to 125 sg1845y sg1845j sg1845l sg1842y/883b sg1844j/883b sg1844l/883b mil- std/883 sg1845y/883b sg1845j/883 sg1845l/883b desc sg1844y/desc sg1844j/desc sg1844f/desc sg1844l/desc note: available in tape & reel. append the lett ers ?tr? to the part number. (i.e. lxsg3844n-tr)
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 copyright ? 2000 rev. 1.6c 2 p roduction d ata s heet absolute maximum ratings (notes 1 & 2) supply voltage (i cc < 30ma) ............................................................... self limiting supply voltage (low impedance source) ........................................................ 30v output current (peak) ....................................................................................... 1a output current (continuous) ....................................................................... 350ma output energy (capacitive load) ....................................................................... 5j analog inputs (v fb , i sense ) ................................................................ -0.3v to +6.3v error amp output sink current ..................................................................... 10ma operating junction temperature hermetic (j, y, f, l packages) ................................................................... 150c plastic (n, m, d, dm packages) ................................................................ 150c storage temperature range .......................................................... -65c to +150c lead temperature (soldering, 10 seconds) .................................................. 300c package pin outs v ref v cc out ut gnd com v fb i sense r t /c t 1 8 27 36 45 m & y package (top view) dm package (top view) v ref v cc out ut gnd com v fb i sense r t /c t 1 8 27 36 45 v ref n.c. v cc v c out ut gnd wr gnd com n.c. v fb n.c. i sense n.c. r t /c t 1 14 213 312 411 510 69 78 d package (top view) m package: thermal resistance-junction to ambient, ja 95c/w n package: thermal resistance-junction to ambient, ja 65c/w dm package: thermal resistance-junction to ambient, ja 165c/w d package: thermal resistance-junction to ambient, ja 120c/w y package: thermal resistance-junction to ambient, ja 130c/w j package: thermal resistance-junction to ambient, ja 80c/w f package: thermal resistance-junction to case, jc 80c/w thermal resistance-junction to ambient, ja 145c/w l package: thermal resistance-junction to case, jc 35c/w thermal resistance-junction to ambient, ja 120c/w junction temperature calculation: t j = t a + (p d x ja ). the ja numbers are guidelines for the thermal performance of the device/pc-board system. all of the above assume no ambient airflow. thermal data note 1. exceeding these ratings could cause damage to the device. note 2. all voltages are with respect to pin 5. all currents are positive into the specified terminal. 1 14 213 312 411 510 69 78 j & n package (top view) com n.c. v fb n.c. i sense n.c. r t /c t v ref n.c. v cc v c out ut ground ower gnd f package (top view) 10.v ref 9. v cc 8. v c 7. out ut 6. gnd 1. com 2. v fb 3. i sense 4. r t /c t 5. ower gnd 1 10 29 38 47 56 l package (top view) 32 4 5 6 7 8 911 10 1. n.c. 2. n.c. 3. com . 4. n.c. 5. v fb 6. n.c. 7. i sense 8. r t /c t 9. n.c. 10. n.c. 12019 18 17 16 15 14 12 13 11. n.c. 12. wr gnd 13. gnd 14. n.c. 15. out ut 16. n.c. 17. v c 18. v cc 19. n.c. 20. v ref rohs / pb-free peak package solder reflow temp. (40 second max. exposure)............................... 260c (+0, -5) rohs / pb-free 100% matte tin lead finish rohs / pb-free 100% matte tin lead finish m package: rohs / pb-free 100% matte tin lead finish n package: rohs / pb-free 100% matte tin lead finish
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 3 copyright ? 2000 rev. 1.6c p roduction d ata s heet electrical characteristics (unless otherwise specified, these specifications apply over the operating ambient temperatures for sg1844/sg1845 with -55c t a 125c, sg2844/ sg2845 with -25c t a 85c, sg3844/sg3845 with 0c t a 70c, v cc = 15v (note 7), r t = 10k ? , and c t = 3.3nf. low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.) reference section parameter symbol test conditions output voltage t j = 25c, i o = 1ma line regulation 12 v in 25v load regulation 1 i o 20ma temperature stability (note 4) total output variation (note 4) line, load, temp. output noise voltage (note 4) v n 10hz f 10khz, t j = 25c long term stability (note 4) t a = 125c, 1000hrs output short circuit sg3844/45 units min. typ. max. min. typ. max. min. typ. max. sg2844/45 4.95 5.00 5.05 4.95 5.00 5.05 4.90 5.00 5.10 v 620 620 620 mv 625 625 625 mv 0.2 0.4 0.2 0.4 0.2 0.4 mv/c 4.90 5.10 4.90 5.10 4.82 5.18 v 50 50 50 v 525 525 525 mv -30 -100 -180 -30 -100 -180 -30 -100 -180 ma oscillator section initial accuracy (note 8) t j = 25c voltage stability 12v v cc 25v temperature stability (note 4) t min t a t max amplitude v rt/ct (peak to peak) discharge current t j = 25c t min t a t max error amp section input voltage v comp = 2.5v input bias current open loop gain a vol 2 v o 4v unity gain bandwidth (note 4) t j = 25c power supply rejection ratio psrr 12 v cc 25v output sink current v vfb = 2.7v, v comp = 1.1v output source current v vfb = 2.3v, v comp = 5v v out high v vfb = 2.3v, r l = 15k to gnd v out low v vfb = 2.7v, r l = 15k to v ref sg1844/45 47 52 57 47 52 57 47 52 57 khz .021 0.21 0.21 % 555% 1.7 1.7 1.7 v 7.8 8.3 9.1 7.5 8.4 9.3 7.5 8.4 9.3 ma 6.8 9.3 7.2 9.5 7.2 9.5 ma 2.45 2.50 2.55 2.45 2.50 2.55 2.42 2.50 2.58 v -0.3 -1 -0.3 1 -0.3 -2 a 65 90 65 90 65 90 db 0.7 1 0.7 1 0.7 1 mhz 60 70 60 70 60 70 db 26 26 26 ma -0.5 -0.8 -0.5 -0.8 -0.5 -0.8 ma 56 56 56 v 0.7 1.1 0.7 1.1 0.7 1.1 v supply voltage range output current (peak) output current (continuous) analog inputs (pin 2, pin 3) error amp output sink current oscillator frequency range oscillator timing resistor r t oscillator timing capacitor c t operating ambient temperature range: sg1844/45 sg2844/45 sg3844/45 recommended operating conditions (note 3) parameter symbol units recommended operating conditions min. typ. max. 30 v 1 a 200 ma 02.6v 5ma 0.1 500 khz 0.52 150 k ? 0.001 1.0 f -55 125 c -25 85 c 070c note 3. range over which the device is functional. (electrical characteristics continue next page.)
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 copyright ? 2000 rev. 1.6c 4 p roduction d ata s heet electrical characteristics (cont'd.) under-voltage lockout section parameter symbol test conditions start threshold 1844 1845 min. operation voltage after turn-on 1844 1845 pwm section maximum duty cycle minimum duty cycle power consumption section start-up current operating supply current v fb = v isense = 0v v cc zener voltage i cc = 25ma notes: 4. these parameters, although guaranteed, are not 100% tested in production. 5. parameter measured at trip point of latch with v vfb = 0. sg3844/45 units min. typ. max. min. typ. max. min. typ. max. sg2844/45 15 16 17 15 16 17 14.5 16 17.5 v 7.8 8.4 9.0 7.8 8.4 9.0 7.8 8.4 9.0 v 9 10 11 9 10 11 8.5 10 11.5 v 7.0 7.6 8.3 7.0 7.6 8.2 7.0 7.6 8.2 v sg1844/45 46 48 50 46 48 50 46 48 50 % 000% 0.5 1 0.5 1 0.5 1 ma 11 17 11 17 11 17 ma 34 34 34 v 6. gain defined as: a = ; 0 v isense 0.8v. 7. adjust v cc above the start threshold before setting at 15v. 8. output frequency equals one half of oscillator frequency. output low level i sink = 20ma i sink = 200ma output high level i source = 20ma i source = 200ma rise time (note 4) t j = 25c, c l = 1nf fall time (note 4) t j = 25c, c l = 1nf current sense section gain (notes 5 & 6) maximum input signal (note 5) v comp = 5v power supply rejection ratio (note 5) psrr 12 v cc 25v input bias current delay to output (note 4) output section 2.85 3 3.15 2.85 3 3.15 2.85 3 3.15 v/v 0.9 1 1.1 0.9 1 1.1 0.9 1 1.1 v 70 70 70 db -2 -10 -2 -10 -2 -10 a 150 300 150 300 150 300 ns 0.1 0.4 0.1 0.4 0.1 0.4 v 1.5 2.2 1.5 2.2 1.5 2.2 v 13 13.5 13 13.5 13 13.5 v 12 13.5 12 13.5 12 13.5 v 50 150 50 150 50 150 ns 50 150 50 150 50 150 ns ? v comp ? v isense
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 5 copyright ? 2000 rev. 1.6c p roduction d ata s heet block diagram * - v cc and v c are internally connected for 8-pin packages. ** - power ground and ground are internally connected for 8-pin packages. oscillator s r internal bias s / r 5v ref pwm latch current sense comparator 1v r 2r error amp uvlo 34v ground** v cc * r t /c t v fb t comp current sense power ground** output v c * v ref 5.0v 50ma 16v (1844) 8.4 (1845) 6v (1844) 0.8v (1845) 2.5v v ref good logic
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 copyright ? 2000 rev. 1.6c 6 p roduction d ata s heet graph / curve index characteristic curves figure # 1. dropout voltage vs. temperature 2. oscillator temperature stability 3. current sense to output delay vs. temperature 4. start-up current vs. temperature 5. reference voltage vs. temperature 6. start-up voltage threshold vs. temperature 7. start-up voltage threshold vs. temperature 8. oscillator discharge current vs. temperature 9. output saturation voltage vs. output current and temperature (sink transistor) 10. current sense threshold vs. error amplifier output 11. output saturation voltage vs. output current and temperature (source transistor) figure index application information figure # 12. oscillator timing circuit 13. oscillator frequency vs. r t for various c t typical applications section figure # 14. current sense spike suppression 15. mosfet parasitic oscillations 16. bipolar transistor drive 17. isolated mosfet drive 18. adjustable buffered reduction of clamp level with softstart 19. external duty cycle clamp and multi-unit synchronization 20. oscillator connection 21. error amplifier connection
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 7 copyright ? 2000 rev. 1.6c p roduction d ata s heet characteristic curves figure 2. ? oscillator temperature stability figure 3. ? current sense to output delay vs. temperature figure 4. ? start-up current vs. temperature figure 1. ? dropout voltage vs. temperature junction temperature - ( c) frequency drift - (%) -10 -75 -50-25 0 255075100125 -8 -6 -4 -2 0 v in = 15v duty cycle = 50% 2 junction temperature - ( c) minimum operating voltage - (v) 8.0 -75 -50-25 0 255075100125 8.4 8.8 9.2 9.6 10.0 sg1844 sg1845 junction temperature - ( c) current sense delay - (ns) 120 -75 -50-25 0 255075100125 140 160 180 200 220 v pin3 = 1.1v junction temperature - ( c) start-up current - (ma) 0.2 -75 -50-25 0 255075100125 0.3 0.4 0.5 0.6 0.7 sg1844 sg1845
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 copyright ? 2000 rev. 1.6c 8 p roduction d ata s heet characteristic curves figure 6. ? start-up voltage threshold vs. temperature figure 7. ? start-up voltage threshold vs. temperature figure 8. ? oscillator discharge current vs. temperature figure 5. ? reference voltage vs. temperature junction temperature - ( c) reference voltage - (v) 8.18 -75 -50-25 0 255075100125 sg1845 8.22 8.26 8.30 8.32 8.20 8.24 8.28 junction temperature - ( c) reference voltage - (v) 4.98 -75 -50-25 0 255075100125 v cc = 15v 4.99 5.00 5.01 5.02 junction temperature - ( c) start up voltage - (v) 16.00 -75 -50-25 0 255075100125 sg1844 16.02 16.04 16.06 16.08 15.98 junction temperature - ( c) oscillator discharge current - (ma) 7.4 -75 -50-25 0 255075100125 7.6 7.8 8.0 8.2 7.2
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 9 copyright ? 2000 rev. 1.6c p roduction d ata s heet characteristic curves figure 10. ? current sense threshold vs. error amplifier output figure 11. ? output saturation voltage vs. output current & temperature figure 9. ? output saturation voltage vs. output current & temperature error amp output voltage - (v) current sense threshold - (v) 0.2 1.0 2.0 3.0 4.0 5.0 0.4 0.6 0.8 1.0 0 0.1 0.3 0.5 0.7 0.9 125c 25c -55c output current - (ma) saturation voltage - (v) 0.5 100 200 300 400 500 1.0 1.5 2.0 2.5 0 -55 c +25 c +125 c v in = 15v duty cycle < 5% output current - (ma) saturation voltage - (v) 1.0 100 200 300 400 500 2.0 3.0 4.0 0 v in = 15v duty cycle < 5% -55 c +25 c +125 c +125 c +25 c
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 copyright ? 2000 rev. 1.6c 10 p roduction d ata s heet application information oscillator the oscillator of the 1844/45 family of pwm's is programmed by the external timing components (rt, ct) as shown in figure 13. figure 12 ? oscillator timing circuit v ref r t /c t gnd r t c t figure 13 ? oscillator frequency vs. r t for various c t 100k 1k 100 10k r t - ( ) oscillator frequency - (hz) 100k 1k 10k 1m 100nf 47nf 22nf 10nf 4.7nf 2.2nf 1nf f where r t 5k ? 1.86 r t c t
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 11 copyright ? 2000 rev. 1.6c p roduction d ata s heet typical application circuits figure 17. ? isolated mosfet drive figure 16. ? bipolar transistor drive current transformers can be used where isolation is required between pwm and primary ground. a drive transformer is then necessary to interface the pwm output with the mosfet. the 1844/45 output stage can provide negative base current to remove base charge of power transistor (q 1 ) for faster turn off. this is accomplished by adding a capacitor (c 1 ) in parallel with a resistor (r 1 ). the resistor (r 1 ) is to limit the base current during turn on. pin numbers referenced are for 8-pin package and pin numbers in parenthesis are for 14-pin package. figure 14. ? current sense spike suppression figure 15. ? mosfet parasitic oscillations a resistor (r 1 ) in series with the mosfet gate reduce overshoot and ringing caused by the mosfet input capacitance and any inductance in series with the gate drive. (note: it is very important to have a low inductance ground path to insure correct operation of the i.c. this can be done by making the ground paths as short and as wide as possible.) the rc low-pass filter will eliminate the leading edge current spike caused by parasitics of power mosfet. v cc v in 7 (12) 7 (11) 6 (10) 5 (8) 3 (5) r c r s q1 i pk i pk(max) = 1.0v r s sg1844/45 v cc v in 7 (12) 7 (11) 6 (10) 5 (8) r s q1 sg1844/45 3 (5) r 1 sg1844/45 3 (5) 5 (8) 6 (10) 7 (11) r s q1 v c1 c 1 r 1 r 2 v in v c i b + v c r 2 v c1 r 1 || r 2 _ v cc v in 7 (12) 7 (11) 6 (10) 5 (8) 3 (5) sg1844/45 isolation boundary c r r s n s n p q1 v gs waveforms + _ 0 + _ 0 50% dc 25% dc i pk = v (pin 1) - 1.4 3r s n p n s ? ? ? ? ? ?
c urrent -m ode pwm c ontroller sg1844/sg1845 series product databook 1996/1997 copyright ? 2000 rev. 1.6c 12 p roduction d ata s heet typical application circuits (continued) figure 19. ? external duty cycle clamp and multi-unit synchronization figure 18. ? adjustable buffered reduction of clamp level with softstart precision duty cycle limiting for a duty cycle of <50%, as well as synchronizing several 1844/45's is possible with the above circuitry. softstart and adjustable peak current can be done with the external circuitry shown above. i pk = where: 0 v 1 1.0v t softstart = -ln 1 - c 7 (12) 6 (10) 7 (11) 5 (8) 3 (5) sg1844/45 v cc v in q1 r s 5 (9) 8 (14) 4 (7) 2 (3) 1 (1) 2n2907 r 2 r 1 1n4148 c 2 6 r b r a 1 84 3 555 timer 4 (7) 5 (9) 8 (14) sg1844/45 to other sg1844/45 c figure 21. ? error amplifier connection figure 20. ? oscillator connection 7 (11) 6 (10) 5v c t 2.8v 1.1v sg1844/45 discharge current i d = 8.2ma r t 1 (1) r f r i 2 (3) r f 10k 2.5v sg1844/45 0.5m a the oscillator is programmed by the values selected for the timing components r t and c t . refer to application information for calculation of the component values. error amplifier is capable of sourcing and sinking current up to 0.5ma. f = (r a + 2r b )c 1.44 f = r a + 2r b r b v 1 r s r 1 r 2 r 1 +r 2 1.43 - 0.23 1+ ? ? ? ? ? ? v c v 2 and v 1 = where: v 2 = r 1 r 2 r 1 r 2 0.5 1+ r 1 r 2

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