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description gm38c4x is fixed frequency, high performance, and cur- rent- mode pwm controllers. gamma's bicmos devices are pin compatible with standard 384x bipolar devices but with several improvements. undervoltage lockout circuitry allows the '42 and '44 ver- sions to start up at 14.5v and operate down to 9v, and the '43 and '45 versions start at 8.4v with operation down to 7.6v. all versions operate up to 16v. when compared to bipolar 384x devices operating from a 15v supply, start-up current has been reduced to 50a typi- cal and operating current has been reduced to 4.0 ma typi- cal. decreased output rise/fall times drive larger mosfet s, and rail-to-rail output capability increases efficiency, espe- cially at lower supply voltages. gm38c4x also features a trimmed oscillator discharge current and bandgap refer- ence. gm38c4x denotes 8-pin plastic dip and sop packages. application current-mode, off-line, switched-mode power supplies current-mode, dc-to-dc converters. step-down "buck" regulators g m 4 3 1 features 40ns output rise and 30ns output fall times -40 to +85 c temp. range same as standard uc284x low-power bicmos process very low start-up current (50a typical) low operating current (4ma typical) cmos outputs with rail-to-rail swing 500khz current-mode operation pin-for-pin compatible with uc3842/ 3843 / 3844/ 3845(a) trimmed oscillator discharge current uvlo with hysteresis low cross-conduction currents g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 www.gammamicro.com 1 step-up "boost" regulators flyback, isolated regulators forward converters synchronous fet converters v 0 . 1
marking information & pin configura tions (top view) a = assembly location y = y ear w w = weekly ordering number package shipping gm38c42s8t gm38c43s8t gm38c44s8t GM38C45S8T gm38c42s8r gm38c43s8r gm38c44s8r gm38c45s8r gm38c42d8t gm38c43d8t gm38c44d8t gm38c45d8t sop - 8 sop - 8 sop - 8 sop - 8 sop - 8 sop - 8 sop - 8 sop - 8 dip-8 dip-8 dip-8 dip-8 100 units/ tube 100 units/ tube 100 units/ tube 100 units/ tube 2,500 units/ t ape & reel 2,500 units/ t ape & reel 2,500 units/ t ape & reel 2,500 units/ t ape & reel 60 units/ tube 60 units/ tube 60 units/ tube 60 units/ tube v dd v ref out gnd r / c tt i sns 2 g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 ordering information * for detail ordering number identification, please see last page. dip - 8 1 2 3 4 5 6 7 8 comp fb gm38cxx ayww sop - 8 1 2 3 4 5 6 7 8 comp fb gm38cxx ayww v dd v ref out gnd r / c tt i sns
package pin description function function comp compensation: connect external compensation network to modify the error amplifier output. pin lead 1 fb feedback (input): error amplifier input .feedback is 2.5vat desired output voltage. 2 i sns current sense (input): current sense comparator input. connect to current sensing resistor or current transformer. 3 r / c tt timing resistor / timing capacitor: connect external rc network to select switching frequency. 4 5 gnd out ground: combined analog and power ground. power output: t otem - pole output. 6 v dd analog supply (input): controller circuitry supply input. return to analog ground (agnd). 5v reference (output): connect external rc network. v ref block diagram 7 8 g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 3 p ara met er sym bol v alu e uni t 30 ma i dd absolute maximum ratings supp ly v oltag e(no te 6) switc h su pply vo ltage curre nt se nse v oltag e feed back vo ltage outp ut cu rrent stora ge t empe ratur e 18 18 - 0.3 to + 5 .5 0.5 v v v v a c v dd v d v isns v fb i out t a - 0.3 to + 5 .5 - 50 to + 1 50 zene r cur rent oper ation at 16v may requ ire sp ecial prec autio ns(n ote6) v dd 7 v ref 8 r / c tt 4 fb 2 35v output 6 5v reference uvlo oscillator 2.5v 2r r s r + - - + q q t comp 1 gnd* 5 i sns 3 * * * 8 - lead versions only - + p ara met er sym bol v alu e uni t 150 t j operating ra tings junc tion t empe ratur e c
power management g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 4 electrical characteristics (t = -40c to 85 , note 4, v = 15v, c =3.3 nf, r =10k w , unless otherwise noted ) a dd t t c characteristics test conditions min typ max unit output voltage line regulation reference section t = 25c, i = 1ma ao 4.9 5.0 2 v mv 5.1 20 12v v 16v, i = 5a, (note 6) dd o load regulation 1 mv 25 1 i 20ma o temp. stability 0.2 mv / c (note 1) total output v ariation line, load, t emp.,note 1 4.82 5.18 v output noise voltage 50 v 10hz f 10khz, t = 25c, (note 1) a long term stability 5 mv t = 125c, 1000hrs., (note 1) a 25 output short circuit -80 ma -180 -30 oscillator section initial accuracy 52 khz 55 49 t = 25c, (note 5) a voltage stability 0.2 % 1.0 12 v 16v, (note 6) dd temp. stability 0.04 % / c t t t , (note 1) min a max clock ramp reset current t t t min a max t = 25c, v = 2v, a rt/ct 7.7 7.2 8.4 8.4 9.0 9.5 ma amplitude 1.9 vp-p v (peak to peak) rt/ct error amplifier section input current -0.1 a v = 5v fb -2 input voltage 2.5 v v = 2.5v comp 2.58 2.42 open loop voltage gain db 65 2v v 4v o power supply rejection ratio 60 12v v 16v dd db output sink current 14 2 v = 2.7v, v = 1.1v fb comp ma output source current -1 -0.5 v = 2.3v, v = 5v fb comp ma high output voltage 6.6 5.0 v = 2.3v, r = 15k to gnd fb l v low output voltage 0.1 v = 2.7v, r = 15k to v fb l ref v 1.1 1.0 (note 1) mhz current sense section gain note 2 and 3 maximum threshold 1.0 v v = 5v, (note 2) comp 1.1 2.85 psrr 70 db 0.9 input bias current -1.0 12v v 16v, (note 2) dd delay to output 120 a -2 250 ns 0.7 3.0 3.15 v / v unity gain bandwidth 90
g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 5 electrical characteristics (t = -40c to 85c, note 4, v = 15v, c =3.3 nf, r =11k w , unless otherwise noted ) a dd t t test conditions typ max unit characteristics test conditions min output section undervoltage lockout section pwm section total standby current r high ds(on) r low ds(on) start threshold maximum duty cycle start - up current minimum operating voltage rise time fall time i = 200ma source gm38c42, gm38c44 v = 13v for gm38c42, gm38c44 dd v = 7.5v for gm38c43, gm38c45 dd i = 200ma sink t = 25c, c = 1nf al t = 25c, c = 1nf al 20 14.5 96 50 9 11 8.4 50 7.6 40 30 80 60 w a ns ns minimum duty cycle operating supply current zener voltage (v ) dd v = v = 0v fb isns i = 25 ma, note 6 dd 4 37 0 6 % ma v gm38c43, gm38c45 gm38c42, gm38c44 gm38c43, gm38c45 13.5 8 7.8 7.0 15.5 10 9.0 8.2 v v gm38c42, gm38c43 gm38c44, gm38c45 94 46 % 200 30 note 1: these parameters, although guaranteed, are not 100% tested in production. note 2: parameter measured at trip point of latch with v = 0. ea note 3: gain defined as: a = ; 0 v (i ) 0.8v th sns note 4: adjust v above the start threshold before setting at 15v. dd note 5: output frequency equals oscillator frequency for the gm38c42 and gm38c43. output frequency for the gm38c44, and gm38c45 equals one half the oscillator frequency. note 6: on 8-pin version, 18v is maximum input on pin 7, as this is also the supply pin for the output stage. d v pin1 v (i ) th sns
6 g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 typical performance characteristics 100 10 1 4 5 5 1x10 1x10 5x10 oscillator frequency (hz) r r e s i s t a n c e ( k w ) t 200pf 470pf 1nf 1.8nf 4.7nf 10nf v = 15v dd figure 1. oscillator frequency configuration 100 10 1 4 5 6 1x10 1x10 1x10 frequency (hz) o u t p u t d e a d t i m e ( % ) 200pf 470pf 1nf 18nf 4.7nf 10nf v = 15v dd figure 2. gm38c42, gm38c43 output dead time vs. oscillator frequency 9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0 -60 -30 0 30 60 90 120 150 temperature (c) o s c . d i s c h a r g e c u r r e n t ( m a ) figure 3. oscillator discharge current vs. temperature v = 15v dd v = 2v osc 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 2 4 6 8 error amplifier output (v) c u r r e n t s e n s e a m p t h r e s h o l d ( v ) 125c -50c 25 c figure 4. current sense amplifier vs. error amplifier output 120 100 80 60 40 20 0 -60 -30 0 30 60 90 120 150 temperature (c) v s h o r t c u r c u i t c u r r e n t ( m a ) r e f figure 5. short - circuit reference current vs. temperature v = 15v dd 25 20 15 10 5 0 -5 -10 -15 0.0 0.2 0.4 0.6 0.8 1.0 time (s) o u t p u t v o l t a g e ( v ) figure 6. gm38c4x output waveform v = 15v d c = 1nf l
g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 7 application information familiarity with 384x converter designs is assumed. gm38c4x has been designed to be compatible with 384xa series controllers. gm38c4x advantages start-up current start-up current has been reduced to an ultra-low 50a(typical) permitting higher-valued, lower-wattage, and start-up resistors (power controller during power supply start-up). the reduced resistor wattage reduces cost and printed circuit space. operating current operating current has been reduced to 4ma compared to 1 1ma for a typical bipolar controller . the controller runs cooler and the v hold-up capacitance required during start-up may be reduced. dd output driver complementary internal p-and n-channel mosfet s produce rail-to-rail output voltages for better performance driving external power mosfet s. the driver transistor's low on resistance and high peak current capability can drive gate capacitances of greater than 1000pf . the value of output capacitance which can be driven is determined only by the rise/fall time requirements. within the restrictions of output capacity and controller power dissipation, maximum switching frequency can approach 500khz. design precautions when operating near 20v, circuit transients can easily exceed 20v absolute maximum rating and permanently damaging the controller's cmos construction. t o reduce transients, use a 0.1f low-esr capacitor to next to the controller's supply v (or v for '-1' versions)and ground connections. dd d film type capacitors, such as wima mks2, are recommended. when designing high -frequency converters, avoid capacitive and inductive coupling of the switching waveform into high impedance circuitry such as the error amplifier, oscillator , and current sense amplifier. avoid long printed-circuit traces and component leads. locate oscillator and compensation circuitry neat the ic. use high frequency decoupling capacitors on v , and if necessary, on v . return high di/dt currents directly to their erf dd source and use large ground planes. buck converter refer to figure 7. when at lest 26v is applied to the input, c5 is charged through r2 until the voltage v is dd greater than 14.5v(the undervoltage lockout value of the gm38c42), output switching begins when q1is turned on by the gate drive transformer t1 and charging the output filter capacitor c3 through l1. d5 supplies a regulated +12v to v once the circuit is running. dd current sense transformer ct1 provides current feedback to isns for current-mode operation and cycle-by-cycle current limiting. this is more efficient than a high- power sense resistor and provides the required ground- referenced level shift. when q1 turns off, current flow continues from ground through d1 and l1 until q1 is turned on again. the 100v schottky diode d1 reduces the forward voltage drop in the main current path, resulting in higher efficiency than could be accomplished by using an ultra-fast recovery diode. r1 and c2 suppress parasitic oscillations from d1. using a high-value inductance for l1 and a low-esr capacitor for c3 permits small capacitance with minimum output ripple. this inductance value also improves circuit efficiency by reducing the flux swing in l1. magnetic components are carefully chosen for minimal loss at 500khz.
8 g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 v in 26v to 40v r2 68k d2 m17z105 1/4w 0.22f 6.8k 100k r4 18 gm38c42 1 2 3 4 8 7 6 5 c7 200pf r5 16k 0.1f comp fb i sns r/ c tt v ref v dd out gnd ct1 0.1f* mks2 c5 4.7 f q1 irf820 d4 1n765b t1 c8 0.1 f r1 10 1/2w c2 1000pf d5 1n4001 6.19k 1% 1.62k 1% c3 3.3 f c4 0.1 f v out 12v, 2a d3 mbr030 4.7 w l1 48 h 31dq10 d1 figure 7. 500khz, 25w, buck converter test conditions results line regulation load regulation efficiency output ripple v = 26v to 80v, i = 2a in o v = 48v, i = 0.2a to 2a in o v = 48v, i = 2a in o v = 48v, i = 2a (20mhz bw) in o 0.5% 0.6% 90% 100mv 0.1 f + * locate near gm38c42 supply pins
g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 9 0.275 7.0 0.155 4.0 0.060 1.52 0.050 1.270 0.024 0.6 inches mm ( ) pad layout sop-8 p ackage outline dimensions 0.236 0.008 0.050 nom 1.270 nom +0.21 -0.20 5.990 3.91 0.1 +0.003 -0.004 0.154 pin indent 1.600 0.130 0.063 0.005 0.057 nom 1.450 nom 0.175 0.075 0.007 0.003 +0.004 -0.003 0.016 +0.10 -0.08 0.410 +0.0018 -0.0005 0.008 +0.05 -0.01 0.200 +0.013 -0.022 0.028 +0.33 -0.56 0.710 +0.002 -0.004 0.191 +0.05 -0.10 4.850 inches mm ( ) 0 ~ 8 dip-8 p ackage outline dimensions 0.015 min 0.380 min 0.26 0.006 +0.15 -0.16 6.60 0.36 0.01 +0.25 -0.26 9.14 0.180 max 4.570 max 0.125 min 3.180 min +0.002 -0.006 0.13 +0.05 -0.15 3.30 0.018 0.004 0.46 0.10 0.039 0.07 0.99 0.18 0.06 0.01 +0.26 -0.25 1.52 0.100 nom 2.540 nom 0.021 0.005 +0.12 -0.13 0.53 +0.010 -0.015 0.30 +0.25 -0.38 7.62 +0.002 -0.003 0.01 +0.05 -0.08 0.25 0.365 0.02 9.27 0.51 inches mm ( )
10 g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 ordering number gm 38 4x c s8 r gamma micro. circuit type bicoms process package s8: sop-8 d8: dip-8 shipping t : tube r: t ape & reel
g m 3 8 c 4 2 , g m 3 8 c 4 3 , g m 3 8 c 4 4 , g m 3 8 c 4 5 11

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