mic38c42a/43a/44a/45a micrel april 2002 1 mic38c42a/43a/44a/45a mic38c42a/43a/44a/45a bicmos current-mode pwm controllers final information general description the mic38c4xa are fixed frequency, high performance, current-mode pwm controllers. micrel? bicmos devices are pin compatible with 384x bipolar devices but feature several improvements. undervoltage lockout circuitry allows the ?2 and ?4 versions to start up at 14.5v and operate down to 9v, and the ?3 and ?5 versions start at 8.4v with operation down to 7.6v. all versions operate up to 20v. when compared to bipolar 384x devices operating from a 15v supply, start-up current has been reduced to 50 a typical and operating current has been reduced to 4.0ma typical. decreased output rise and fall times drive larger mosfets, and rail-to-rail output capability increases effi- ciency, especially at lower supply voltages. the mic38c4xa also features a trimmed oscillator discharge current and bandgap reference. the mic38c4xa family is available in 8-pin soic and msop- 8 (mm8) package options for fast rise and fall times and higher output drive, refer to the mic38hc4x. functional diagram features fast 40ns output rise and 30ns output fall times ?0 c to +85 c temperature range meets uc284x specifications high-performance, low-power bicmos process ultralow start-up current (100 a typical) low operating current (4ma typical) cmos outputs with rail-to-rail swing 500khz current-mode operation trimmed 5v bandgap reference pin-for-pin compatible with uc3842/3843/3844/3845 trimmed oscillator discharge current uvlo with hysteresis low cross-conduction currents applications current-mode, off-line, switched-mode power supplies current-mode, dc-to-dc converters. step-down ?uck?regulators step-up ?oost?regulators flyback, isolated regulators forward converters synchronous fet converters tq s r q r 2r oscillator uvlo 5v reference vdd 7 vref 8 rt/ct 4 fb 2 2.5v comp 1 gnd 5 isns 3 out 6 ? mic38c42a, mic38c43a (96% max. duty cycle) versions only mic38c44a, mic38c45a (50% max. duty cycle) versions only ? mm8 is a trademark of micrel, inc. micrel, inc. ?1849 fortune drive ?san jose, ca 95131 ?usa ?tel + 1 (408) 944-0800 ?fax + 1 (408) 944-0970 ?http://www.mic rel.com
mic38c42a/43a/44a/45a micrel mic38c42a/43a/44a/45a 2 april 2002 ordering information part number temperature range package mic38c42abm 40 c to +85 c 8-pin soic mic38c43abm 40 c to +85 c 8-pin soic mic38c44abm 40 c to +85 c 8-pin soic mic38c45abm 40 c to +85 c 8-pin soic mic38c42abmm 40 c to +85 c 8-pin mm8 mic38c43abmm 40 c to +85 c 8-pin mm8 mic38c44abmm 40 c to +85 c 8-pin mm8 mic38c45abmm 40 c to +85 c 8-pin mm8 uvlo thresholds startup 8.4v startup 14.5v duty cycle minimum operating 7.6v minimum operating 9v 0% to 96% mic38c43a mic38c42a 0% to 50% mic38c45a mic38c44a selection guide refer to the part number cross reference for a listings of micrel devices equivalent to uc284x and uc384x devices.
mic38c42a/43a/44a/45a micrel april 2002 3 mic38c42a/43a/44a/45a pin description pin number pin name pin function 1 comp compensation: connect external compensation network to modify the error amplifier output. 2 fb feedback (input): error amplifier input. feedback is 2.5v at desired output voltage. 3 isns current sense (input): current sense comparator input. connect to current sensing resistor or current transformer. 4 rt/ct timing resistor/timing capacitor: connect external rc network to select switching frequency. 5 gnd ground: combined analog and power ground. 6 out power output: totem-pole output. 7 vdd analog supply (input): controller circuitry supply input. return to analog ground (agnd). 8 vref 5v reference (output): connect external rc network. 1 2 3 4 8 7 6 5 comp fb isns rt/ct vref vdd out gnd mic38c4xa 8-lead soic (m) 8-lead mm8 (mm) pin configuration
mic38c42a/43a/44a/45a micrel mic38c42a/43a/44a/45a 4 april 2002 electrical characteristics v dd = 15v, note 4 ; r t = 11.0k; c t = 3.3nf; 40 c t a 85 c; unless noted parameter test conditions min typ max units reference section output voltage t a = 25 c, i o = 1ma 4.90 5.00 5.10 v line regulation 12v v dd 18v, i o = 5 a220mv load regulation 1 i o 20ma 1 25 mv temp. stability note 1 0.2 mv/ c total output variation line, load, temp., note 1 4.82 5.18 v output noise voltage 10hz f 10khz, t a = 25 c, note 1 50 v long term stability t a = 125 c, 1000 hrs., note 1 525mv output short circuit 30 80 180 ma oscillator section initial accuracy t a = 25 c, note 5 47 53 59 khz voltage stability 12 v dd 18v 0.2 1.0 % temp. stability t min t a t max , note 1 0.04 %/ c clock ramp t a = 25 c, v rt/ct = 2v, note 1 7.7 8.4 9.0 ma reset current amplitude v rt/ct peak to peak 1.9 vp-p error amp section input voltage v comp = 2.5v 2.4 2.50 2.58 v input bias current v fb = 5.0v 0.1 2 a a vol 2 v o 4v 65 90 db unity gain bandwidth note 1 0.7 1.0 mhz psrr 12 v dd 18v 60 db output sink current v fb = 2.7v, v comp = 1.1v 2 14 ma output source current v fb = 2.3v, v comp = 5v 0.3 1ma v out high v fb = 2.3v, r l = 15k to ground 5 6.8 v v out low v fb = 2.7v, r l = 15k to v ref 0.1 1.1 v absolute maximum ratings supply voltage (v dd ) .................................................... 20v switch supply voltage (v d ) .......................................... 20v current sense voltage (v isns ) ..................... 0.3v to 5.5v feedback voltage (v fb ) ................................ 0.3v to 5.5v output current (i out ) ................................................... 0.5a storage temperature (t a ) ....................... 65 c to +150 c operating ratings junction temperature (t j ) ........................................ 150 c package thermal resistance 8-pin mm8 ( ja ) ............................................. 250 c/w 8-pin soic ( ja ) ...............................................170 c/w
mic38c42a/43a/44a/45a micrel april 2002 5 mic38c42a/43a/44a/45a parameter test conditions min typ max units current sense gain notes 2, 3 2.85 3.0 3.15 v/v maximumthreshold v comp = 5v, note 2 0.9 1 1.1 v psrr 12 v dd 18v, note 2 70 db input bias current 0.1 2 a delay to output 120 250 ns output r ds(on) high i source = 200ma 20 ? r ds(on) low i sink = 200ma 11 ? rise time t a = 25 c, c l = 1nf 40 80 ns fall time t a = 25 c, c l = 1nf 30 60 ns undervoltage lockout start threshold mic38c42a/4a 13.5 14.5 15.5 v mic38c43a/5a 7.8 8.4 9.0 v minimum operating voltage mic38c42a/4a 8 9 10 v mic38c43a/5a 7.0 7.6 8.2 v pulse width modulator maximum duty cycle mic38c42a/3a 94 96 % mic38c44a/5a 46 50 % minimum duty cycle 0% total standby current start-up current v dd = 13v for mic38c42a/44a 100 230 a v dd = 7.5v for mic38c43a/45a operating supply current v fb = v isns = 0v 4.0 6.0 ma note 1: these parameters, although guaranteed, are not 100% tested in production. note 2: parameter measured at trip point of latch with v ea = 0. note 3: gain defined as: note 4: adjust v dd above the start threshold before setting at 15v. note 5: output frequency equals oscillator frequency for the mic38c42 and mic38c43. output frequency for the mic38c44a, and mic38c45a equals one half the oscillator frequency.
mic38c42a/43a/44a/45a micrel mic38c42a/43a/44a/45a 6 april 2002 typical characteristics 1 10 100 1x10 4 1x10 5 5x10 5 r t resistance (k ? ) oscillator frequency (hz) oscillator frequency configuration 10nf 4.7nf 1nf 470pf 200pf 1.8nf v dd = 15v 1 10 100 1x10 4 1x10 5 1x10 6 output dead time (%) frequency (hz) mic38c42/43 output dead time vs. oscillator frequency v dd = 15v 10nf 4.7nf 200pf 470pf 18nf 1nf 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8 9.0 -60 -30 0 30 60 90 120 150 osc. discharge current (ma) temperature ( c) oscillator discharge current vs. temperature v dd = 15v v osc = 2v 0.0 0.2 0.4 0.6 0.8 1.0 1.2 02468 current sense amp threshold (v) error amplifier output (v) current sense amplifier vs. error amplifier output -50 c 25 c 125 c 0 20 40 60 80 100 120 -60 -30 0 30 60 90 120 150 v ref short curcuit current (ma) temperature ( c) short-circuit reference current vs. temperature v dd = 15v -15 -10 -5 0 5 10 15 20 25 0.0 0.2 0.4 0.6 0.8 1.0 output voltage (v) time ( s) mic38c4x output waveform v d = 15v c l = 1nf
mic38c42a/43a/44a/45a micrel april 2002 7 mic38c42a/43a/44a/45a mended. 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 cir- cuitry near the ic. use high frequency decoupling capacitors on v ref , and if necessary, on v dd . return high d i/ d t currents directly to their source and use large area ground planes. buck converter refer to figure 1. when at least 26v is applied to the input, c5 is charged through r2 until the voltage v dd is greater than 14.5v (the undervoltage lockout value of the mic38c42). output switching begins when q1 is turned on by the gate drive transformer t1, charging the output filter capacitor c3 through l1. d5 supplies a regulated +12v to v dd once the circuit is running. 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 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 capaci- tor for c3 permits small capacitance with minimum output ripple. this inductance value also improves circuit efficiency by reducing the flux swing in l1. application information familiarity with 384x converter designs is assumed. mic38c4x advantages start-up current start-up current has been reduced to an ultra-low 50 a (typical) permitting higher-valued, lower-wattage, start-up resistors (powers 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 11ma for a typical bipolar controller. the controller runs cooler and the v dd hold-up capacitance required during start-up may be reduced. output driver complementary internal p- and n-channel mosfets pro- duce rail-to-rail output voltages for better performance driving external power mosfets. 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 switch- ing frequency can approach 500khz. design precautions when operating near 20v, circuit transients can easily ex- ceed the 20v absolute maximum rating, permanently damag- ing the controller s cmos construction. to reduce tran- sients, use a 0.1 f low-esr capacitor to next to the controller s supply v dd (or v d for -1 versions) and ground connections. film type capacitors, such as wima mks2, are recom- figure 1. 500khz, 25w, buck converter v out 12v, 2a comp fb isns rt/ct gnd out vdd vref c2 1000pf r1 10 1/2w 31dq10 d1 l1 48 h c3 3.3 f c4 0.1 f 6.19k 1% 1.62k 1% r4 18 c7 200pf r5 16k 0.1 f d3 mbr030 c8 0.1 f t1 6.8k 0.22 f 100k q1 irf820 0.1 f c5 4.7 f r2 68k d2 m17z105 1/4w d5 1n4001 d4 1n765b v in 26v to 40v ct1 4.7 ? mic38c42a 1 2 3 4 8 7 6 5 0.1 f* *locate near mic38c42 supply pins mks2
mic38c42a/43a/44a/45a micrel mic38c42a/43a/44a/45a 8 april 2002 magnetic components are carefully chosen for minimal loss at 500khz. ct1 and t1 are wound on magnetics, inc. p-type material toroids. l1 is wound on a siemens n49 efd core. symbol custom coil 1 ets 2 ct1 4923 ets 92420 t1 4924 ets 92419 l1 4925 ets 92421 1. custom coils, alcester, sd tel: (605) 934-2460 2. energy transformation systems, inc. tel: (415) 324-4949. test conditions results line regulation v in = 26v to 80v, i o = 2a 0.5% load regulation v in = 48v, i o = 0.2a to 2a 0.6% efficiency v in = 48v, i o = 2a 90% output ripple v in = 48v, i o = 2a (20mhz bw) 100mv synchronous buck converter refer to figure 2. this mic38c43 synchronous buck con- verter uses an mic5022 half-bridge driver to alternately drive the pwm switch mosfet (driven by gateh, or high-side output) and a mosfet which functions as a synchronous rectifier (driven by the gatel, or low-side output). the low-side mosfet turns on when the high-side mosfet is off, allowing current to return from ground. current flows through the low-side mosfet in the source to drain direc- tion. the on-state voltage drop of the low-side mosfet is lower than the forward voltage drop of an equivalent schottky rectifier. this lower voltage drop results in higher efficiency. a sense resistor (5m ? ) is connected to the driver s high-side current sense inputs to provide overcurrent protection. refer to the mic5020, mic5021, and mic5022 data sheets for more information. figure 2. 100khz, synchronous buck converter mic38c43a 0.1 f 300k 4.3k v out 5v, 8a 0.15 f 35 h 1000 f low esr 0.1 f smp60n06-14 vdd vref gnd comp vout rt/ct fb isns 4.7nf 10k 10k 6.8k 47k 3.3k 2200 pf 470 f 25v mic5022 vb gateh sh+ gatel sh sl+ ct gnd en flt vdd +12v 5m ? 0.1 f* mks2 *locate near the mic38c43 supply pins. nc nc in nc sl
mic38c42a/43a/44a/45a micrel april 2002 9 mic38c42a/43a/44a/45a package information 45 0 8 0.244 (6.20) 0.228 (5.79) 0.197 (5.0) 0.189 (4.8) seating plane 0.026 (0.65) max ) 0.010 (0.25) 0.007 (0.18) 0.064 (1.63) 0.045 (1.14) 0.0098 (0.249) 0.0040 (0.102) 0.020 (0.51) 0.013 (0.33) 0.157 (3.99) 0.150 (3.81) 0.050 (1.27) typ pin 1 dimensions: inches (mm) 0.050 (1.27) 0.016 (0.40) 8-pin sop (m) 0.008 (0.20) 0.004 (0.10) 0.039 (0.99) 0.035 (0.89) 0.021 (0.53) 0.012 (0.03) r 0.0256 (0.65) typ 0.012 (0.30) r 5 max 0 min 0.122 (3.10) 0.112 (2.84) 0.120 (3.05) 0.116 (2.95) 0.012 (0.03) 0.007 (0.18) 0.005 (0.13) 0.043 (1.09) 0.038 (0.97) 0.036 (0.90) 0.032 (0.81) dimensions: inch (mm) 0.199 (5.05) 0.187 (4.74) 8-pin msop (mm) micrel inc. 1849 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 web http://www.micrel.com this information is believed to be accurate and reliable, however no responsibility is assumed by micrel for its use nor for an y infringement of patents or other rights of third parties resulting from its use. no license is granted by implication or otherwise under any patent or pat ent right of micrel inc. ? 2002 micrel incorporated
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