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cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 1 general description features the cm3842/43 are fixed frequency current-mode pwm controllers specially designed for off-line switching power supply and dc-to-dc converters with a minimum number of external components. these devices feature a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator, and high current totem pole output which is suitable for driving mosfets. the under voltage lock-out (u.v.l.o.) is designed to operated with 200 a typ. start-up current, allowing an efficient bootstrap supply voltage design. the u.v.l.o. thresholds for the cm3842 are 16v (on) and 10v (off) which are ideal for off-line applications. the corresponding typical threshold for the CM3843 are 8.4v (on) and 7.6v (off). the cm3842/43 can operated within 100% duty cycle. low start-up current ( typ. 200 a) optimized for off-line and dc-to-dc converters maximum duty cycle u.v.l.o. with hysteresis operating frequency up to 500khz internal trimmed bandgap reference high current totem pole output error amplifier with low output resistance available in 8-pin plastic dip and surface mount 8-pin s.o.i.c. applications pin configuration off-line flyback or forward converters. dc-to-dc buck or boost converter. monitor power supply 8-pin pdip (top view) available options device start-up voltage hysteresis max. duty cycle cm3842 16v 6v < 100% CM3843 8.4v 0.8v < 100% 8-pin s.o.i.c. (top view) comp v f b i sense v ref gnd output v cc r t /c t comp v f b i sense v ref gnd output v cc r t /c t
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 2 ordering information part number temperature range package cm3842/43cp 0 to 70 8-pin pdip(p08) cm3842/43cs 0 to 70 8-pin soic(s08) block diagram note 1 :v cc and pwr v c are internally connected for 8 pin packages. note 2 :pwr gnd and gnd are internally connected for 8 pin packages. note 3 :u.v.l.o. is 16v for 3842 and 8.4v for 3843. note 4 :hysteresis is 6v for 3842 and 0.8v for 3843. v ref internal bias 36v 2r en 5v v ref u.v.l.o. v ref good logic error amp current sense c oscillator r 1 v r s pwm latch v fb current sense r t /c t pwr gnd output pwr v c gnd v cc comp t 1 2 3 4 8 5 6 7 5 7
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 3 absolute maximum ratings supply voltage, v cc 35v output current, i o 1a analog inputs, v i -0.3v to 6.3v error amp output sink current, i sink(ea) 10ma power dissipation (t a = 25 o c), p d 1w maximum junction temperature t j 150 o c storage temperature range -65 o c to 150 o c lead temperature (soldiering, 10 seconds) 260 o c note 5: exceeding these ratings could cause damage to the device. all voltages are with respect to ground. currents are positive into, negative out of the specified terminal. thermal data pdip package : thermal resistance-junction to ambient, ja 95 o c/w soic package : thermal resistance-junction to ambient, ja 165 o c/w junction temperature calculation: t j = t a + (p d ja ). the ja numbers are guidelines for the thermal performance of the device/pc-board system. all of the above assume no ambient airflow.
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 4 recommended operating conditions recommended operating parameter symbol min. typ. max. units supp l y v o l tage v cc / v c 30 v v i , r t /c t input voltage v i , i sense / v fb 0 5.5 v out p ut volta g e v o , out p ut 0 30 v su pp l y current i cc 25 ma avera g e out p ut current i o 200 ma reference out p ut current i o(ref) -20 ma timin g ca p acitor c t 1 nf oscillator fre q uenc y f osc 100 500 khz o p eratin g free-air tem p erature t a 0 70 o c electrical characteristics unless otherwise specified, these specifications apply over the operating ambient temperature for cm384x with 0 o c t a 70 o c; v cc = 15v(note 7); r t = 10k;c t = 3.3nf. low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature. cm384x parameter symbol test conditions min. typ. max. units reference section reference output voltage v ref t j = 25 o c, i ref = 1ma 4.9 5.0 5.1 v line regulation 12v v cc 25v,t j = 25 o c 6 20 mv load regulation 1ma i ref 20ma 6 25 mv short ciruit output current i sc t j = 25 o c - 30 - 100 - 180 ma oscillator section oscillation frequency f t j = 25 o c 47 52 57 khz fre q uenc y chan g e with volta g e 12v v cc 25v 0.2 1.0 % frequency change with temperature (note 8) t min t a t max 5 % peak-to-peak amplitude at r t /c t v osc 1.7 v current sense section gain (note 9 & 10) a vol 2.85 3.00 3.15 v/v maximum input signal (note 9) v i(max) comp = 5v 0.9 1.0 1.1 v power supply rejection ratio (note 9) psrr 12v v cc 25v (note 9) 70 db input bias current i bias - 3.0 - 10 a
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 5 electrical characteristics (continued) error amplifier section input bias current i bias - 0.1 - 2 a input voltage v i(ea) comp = 2.5v 2.42 2.50 2.58 v open loop voltage gain g vo 2v v o 4v 65 90 db unity gain bandwidth (note 8) ugbw t j = 25 o c 0.7 1 mhz power supply rejection ratio psrr 12v v cc 25v 60 70 db output sink current i sink v fb = 2.7v, comp = 1.1v 2 7 ma output source current i source v fb = 2.3v, comp = 5.0v - 0.5 - 1.0 ma high output voltage v oh v fb = 2.3v, r l = 15k ? to gnd 5 6 v low output voltage v ol v fb = 2.7v, rl = 15k ? to v ref 0.7 1.1 v output section i sink = 20ma 0.1 0.4 output low level v ol i sink = 200ma 1.4 2.2 v i source = 20ma 13 13.5 output high level v oh i source = 200ma 12 13.0 v rise time (note 8) t r t j = 25 o c, c l = 1nf 50 150 ns fall time (note 8) t f t j = 25 o c, c l = 1nf 50 150 ns under - voltage lockout section cm3842 14.5 16.0 17.5 start threshold v th(st) CM3843 7.8 8.4 9.0 v cm3842 8.5 10 11.5 min. operating voltage CM3843 7.0 7.6 8.2 v pwm section cm3842/43 94 97 100 maximum duty cycle % minimum duty cycle 0 % total standby current cm3842 0.2 0.35 startup current CM3843 0.5 1.0 ma operating supply current i cc v fb = i sense = 0v 14 17 ma zener voltage v z i cc = 25ma 30 35 v note 7: adjust v cc above the start threshold before setting at 15v note 8: these parameters, although guaranteed, are not 100% tested in production prior to shipment note 9: parameters are measured at trip point of latch with v fb = 2v note 10: gain is measured between i sense and comp with the input changing from 0v to 0.8v
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 6 application information fig. 1. current sense circuit peak current (i s ) is set by: i s(max) = 1v/r s fig. 3. oscillator section 1.72 fig. 2. error amplifier configuration - the amplifier can source or sink up to 0.5ma for r t < 5k, f = r t c t fig. 4. open-loop laboratory test fixture: careful grounding techniques are necessary for high peak currents associated with capacitive loads. timing and bypass c apacitors should be connected to gnd pin in a single point ground. the transistor and 5k potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to the i sense pin gnd i sense comp error am p r s r f c f r 2r 1v current sense comparator 4.7k 1 k error amp ad j ust 4.7k 2n2222 100k 5 k i sense adjust comp v fb i sense r t /c t gnd v re f v cc output 0.1 f output 1k, 1w v cc v ref 0.1 f gnd c t r t 2.5v z f z i 0.5ma v fb comp error am p gnd r t /c t v ref c t r t
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 7 application information (continued) fig. 5. shutdown techniques - there are two ways to shutdown the pwm controller: 1) raise the voltage at i sense above 1v or, 2) pull the comp below a voltage two diodes above ground. fig 6. slop compensation ? to achieve duty cycles over 50% for some applications , the above slope compensation technique is suggested by resistively summing a fraction of the oscillator ramp with the current sense signal. i sense shutdown v ref 500 ? ? ? ? to current sense resistor 330 ? ? ? ? 1k shutdown comp v ref r t /c t i sense r t c t 0.1 f c r 2 r 1 i sense r sense
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 8 typical characteristics oscillator frequency and frequemcy variation 1 0 1 00 1 ,000 1 0,000 1 00,000 1 ,000,000 11 0 1 00 1 000 rt-timing resistance (unit: k ohm) f-oscillator frequency and frequency variation 1 uf 0. 1 uf 0.0 1 uf 0.00 1 uf
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 9 8-pin plastic dip inches millimeters min typ max min typ max a 0.355 0.365 0.400 9.02 9.27 10.16 b 0.240 0.250 0.280 6.10 6.35 7.11 c - - 0.210 - - 5.33 d - 0.018 - - 0.46 - f - 0.060 - - 1.52 - g - 0.100 - - 2.54 - h 0.050 - 0.090 1.27 - 2.29 j 0.008 - 0.015 0.20 - 0.38 k 0.115 0.130 0.150 2.92 3.30 3.81 l 0.300 bsc. 7.62 bsc. 1 b 5 4 8 c k f h g d a l m j m - 7o 15o - 7o 15o 8-pin plastic s.o.i.c inches millimeters min typ max min typ max a 0.183 - 0.202 4.65 - 5.13 b 0.144 - 0.163 3.66 - 4.14 c 0.068 - 0.074 1.73 - 1.88 d 0.010 - 0.020 0.25 - 0.51 f 0.015 - 0.035 0.38 - 0.89 g 0.050 bsc 0.050 bsc j 0.007 - 0.010 0.19 - 0.25 k 0.005 - 0.010 0.13 - 0.25 l 0.189 - 0.205 4.80 - 5.21 m - - 8o - - 8o p 0.228 - 0.244 5.79 - 6.20 . seating plan a d f p b k c m l j g
cm3842/3843 c urrent m ode pwm c ontroller 2001/06/27 advanced champion microelectronic corporation page 10 8-pin plastic s.o.i.c. carrier dimensions millimeters a 330 1 dd 1.55 0.1 b 100 1 d1 1.5 0.25 +0.5 c 13.0 -1.0 po 4.0 0.1 d 2.2 1 p1 2.0 0.1 t1 12.5 0.5 ao 6.4 0.1 t2 2.0 0.2 bo 5.2 0.1 +0.3 wc 12.0 -0.1 ko 2.1 0.1 wt 9.3 typ. t 0.30 0.013 p 8.0 0.1 e 1.75 0.1 f 5.5 0.1 t2 t1 c d d1 b a e f wc p po dd ao p1 ko wt t bo
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