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april 2005 1 mic4690 mic4690 micrel mic4690 500khz 1a superswitcher buck regulator general description the mic4690 superswitcher is an easy-to-use, 500khz step-down pwm voltage regulator. the mic4690 achieves over 1a of continuous output current over a wide input voltage range in an 8-lead so (small outline) package. the high switching frequency of the mic4690 allows the smallest surface-mount inductors and capacitors to be used. internal compensation ensures fast transient response and a minimum amount of external components. the mic4690 features a power so-8 package with a special lead frame that allows over 1a of continuous current. the mic4690, housed in an so-8, can replace larger to-220 and to-263 packages in many applications. the mic4690 allows for a high degree of safety. it has a wide input voltage range of 4v to 34v, allowing for it to be used in applications where input voltage transients may be present. built-in safety features include over-current protection, fre- quency foldback protection, and thermal shutdown. the mic4690 is available in an 8-lead so package with a junction temperature range of ?0 c to +125 c. typical application

power sop-8 2.5v adjustable converter
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( power sop-8 )* 1.8v adjustable converter features so-8 package with over 1a output current fixed 500khz operation wide 4v to 34vinput voltage range output voltage adjustable to 1.23v all surface mount solution internally compensated with fast transient response up to 85% efficiency overcurrent protection frequency foldback short-circuit protection thermal shutdown applications simple 1a step-down (buck) regulator replacement of to-220 and to-263 designs 12v to 5v/3.3v/2.5v/1.8v/1.5v conversion 5v to 2.5v/1.8v/1.5v conversion on-card switching regulators hard disk drives cable modems positive-to-negative converters simple battery chargers micrel, inc. ?2180 fortune drive ?san jose, ca 95131 ?usa ?tel + 1 (408) 944-0800 ?fax + 1 (408) 474-1000 ?http://www.mic rel.com superswitcher is a trademark of micrel, inc.
mic4690 micrel mic4690 2 april 2005 pin configuration 1 shdn vin sw fb 8 gnd gnd gnd gnd 7 6 5 2 3 4 sop-8 (m) pin description pin number pin name pin function 1 shdn shutdown (input): logic low enables regulator. logic high (>1.5v) shuts down regulator. 2 vin supply voltage (input): unregulated +4v to +30v continuous supply voltage, with a maximum +34v transient voltage. 3 sw switch (output): emitter of npn output switch. connect to external storage inductor and schottky diode. 4 fb feedback (input): connect to output on fixed output voltage versions, or to 1.23v-tap of voltage-divider network for adjustable version. 5-8 gnd ground ordering information part number standard lead-free voltage temperature range package mic4690bm MIC4690YM adjustable ?0 c to +125 c 8-lead sop
april 2005 3 mic4690 mic4690 micrel electrical characteristics v in = 12v, v out = 5v; i load = 500ma; v shdn = 0v, t j = 25 c, unless otherwise noted. bold values indicate ?0 c t j +125 c. parameter condition min typ max units feedback voltage ( 1%) 1.217 1.230 1.243 v ( 2%) 1.205 1.255 v 8v v in 30v, 0.1a i load 1a, v out = 5v 1.193 1.230 1.267 v 1.180 1.280 v maximum duty cycle v fb = 1.0v 90 93 % quiescent current v fb = 1.5v 7 12 ma standby quiescent current v shdn = 5v (regulator off) 30 100 a v shdn = 12v (regulator off) 1.5 a frequency foldback v fb = 0v 220 300 khz oscillator frequency 450 500 550 khz saturation voltage i out = 1a 1.2 v output leakage current v in = 30v, v shdn = 5v, v sw = 0v 50 500 a v in = 30v, v shdn = 5v, v sw = ?v 4 20 ma short circuit current limit v fb = 0v, v out = 0v, see test circuit 1.3 2.5 3.0 a shutdown pin input logic level regulator off 2 1.5 v regulator on 1.25 0.8 v shutdown pin input current v shdn = 5v (regulator off) ?0 ?.7 10 a v shdn = 0v (regulator on) ?0 ?.5 10 a thermal shutdown @ t j 160 c note 1. exceeding the absolute maximum rating may damage the device. note 2. with input voltages above the operating rating, the device may be damaged if a short-circuit is applied to the output. the devi ce will otherwise not be damaged up to its absolute maximum voltage rating. note 3. absolute maximum rating is intended for voltage transients only, prolonged dc operation is not recommended. note 4. devices are esd sensitive. handling precautions recommended. note 5. measured on 1" square of 1 oz. copper fr4 printed circuit board connected to the device ground leads. absolute maximum ratings (note 1) supply voltage (v in ), note 3 ...................................... +34v shutdown voltage (v shdn ) ............................. ?.3v to v in steady-state output switch voltage (v sw ) ....... ?v to v in feedback voltage (v fb ) .............................................. +12v storage temperature (t s ) ....................... ?5 c to +150 c esd rating .............................................................. note 4 operating ratings (note 2) supply voltage (v in ) ....................................... +4v to +30v junction temperature range (t j ) ........... ?0 c to +125 c package thermal resistance ( ja ), note 5 ........................................................ 63 c/w ( jc ), ................................................................... 20 c/w
mic4690 micrel mic4690 4 april 2005 test circuit sw 18 h vin fb gnd shdn device under test +12v sop-8 5? 4 3 2 1 i current limit test circuit shutdown input behavior off on guaranteed off typical off guaranteed on typical on 0.8v 1.25v 0v 1.5v v in(max) 2v shutdown hysteresis
april 2005 5 mic4690 mic4690 micrel typical characteristics 1.223 1.225 1.227 1.229 1.231 1.233 1.235 1.237 1.239 1.241 1.243 -40 -20 0 20 40 60 80 100120140 voltage (v) temperture ( c) reference voltage vs. temperature v in = 12v v out = 5v i out = 100ma 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 8.5 8.6 -40 -20 0 20 40 60 80 100120140 current (ma) temperature ( c) quiescent current vs. temperature v in = 12.0v v out = 5.0v i out = 0 0 10 20 30 40 50 60 70 80 0 5 10 15 20 25 30 35 40 efficiency (%) input voltage (v) efficiency vs. input volta g e v out = 5v i out = 1a 0 100 200 300 400 500 600 -50 0 50 100 150 frequency (khz) temperature ( c) frequency vs. temperature v in = 12v v out = 5v i out = 100ma 0 50 100 150 200 250 300 -50 0 50 100 150 frequency (khz) temperature ( c) frequency foldback vs. temperature v in = 12v v out = 5v i out = 100ma 5.000 5.005 5.010 5.015 5.020 5.025 0 0.2 0.4 0.6 0.8 1 1.2 1.4 output voltage (v) output current (a) load re g ulation v in = 12v v out = 5v 4.96 4.98 5.00 5.02 5.04 5.06 0 5 10 15 20 25 30 35 40 output voltage (v) input voltage (v) line re g ulation v in = 12v v out = 5v i out = 500ma 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 -40 -20 0 20 40 60 80 100120140 shutdown current ( a) temperature ( c) shutdown current vs. temperature v shdn = v in = 12v v out = 5v 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 -40 0 40 80 120 160 shutdown pin voltage (v) temperature ( c) shutdown hysteresis vs. temperature on off v in = 12.0v v out = 5.0v i out = 100ma 68 70 72 74 76 78 80 0 0.2 0.4 0.6 0.8 1 1.2 1.4 efficiency (%) output current (a) efficiency vs. output current v in = 12.0v v out = 5.0v
mic4690 micrel mic4690 6 april 2005 load transient time (100 s/div) v out (100mv/div) i out (1a/div) v in = 12v v out = 5v 0a 100mv 1.5a functional characteristics 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 5 10 15 20 25 30 35 continuous output current (a) input voltage (v) soa for mic4690* v out = 5v t a = 50 c t j = 125 c t a = 25 c switching frequency foldback time normal operation short circuit operation v sw (shorted) 12v in, 0v out v sw (normal) 12v in, 5v/1a out 500khz 190khz sw in fb gnd shdn d1 1n4148 2.2nf 82 mic4690bm 5678 3 snubber circuit
april 2005 7 mic4690 mic4690 micrel block diagrams sw fb r1 r2 c out v in in v out mic4690 [adj.] internal regulator shdn 500khz oscillator thermal shutdown reset current limit com- parator error amp driver 1.23v bandgap reference vv r1 r2 1 r1 r2 v v 1 v 1.23v out ref out ref ref =+ ? ? ? ? ? ? = ? ? ? ? ? ? ? = adjustable regulator functional description the mic4690 is a variable duty cycle switch-mode regulator with an internal power switch. refer to the block diagrams. supply voltage the mic4690 operates from a +4v to +30v (transients to 34v) unregulated input. highest efficiency operation is from a supply voltage around +12v. see the efficiency curve on page 5. enable/shutdown the shutdown ( shdn ) input is ttl compatible. a logic-low enables the regulator. a logic-high shuts down the internal regulator which reduces the current to typically 1.5 a when v shdn = v in = 12v and 30 a when v shdn = 5v. see ?hutdown input behavior: shutdown hysteresis. feedback fixed-voltage versions of the regulator have an internal resistive divider from the feedback ( fb ) pin. connect fb directly to the output voltage. adjustable versions require an external resistive voltage divider from the output voltage to ground, center tapped to the fb pin. see figure 1b for recommended resistor values. duty cycle control a fixed-gain error amplifier compares the feedback signal with a 1.23v bandgap voltage reference. the resulting error amplifier output voltage is compared to a 500khz sawtooth waveform to produce a voltage controlled variable duty cycle output. a higher feedback voltage increases the error amplifier output voltage. a higher error amplifier voltage (comparator inverting input) causes the comparator to detect only the peaks of the sawtooth, reducing the duty cycle of the com- parator output. a lower feedback voltage increases the duty cycle. the mic4690 uses a voltage-mode control architec- ture. output switching when the internal switch is on, an increasing current flows from the supply v in, through external storage inductor l1, to output capacitor c out and the load. energy is stored in the inductor as the current increases with time. when the internal switch is turned off, the collapse of the magnetic field in l1 forces current to flow through fast recovery diode d1, charging c out . output capacitor external output capacitor c out provides stabilization and reduces ripple. return paths during the on portion of the cycle, the output capacitor and load currents return to the supply ground. during the off portion of the cycle, current is being supplied to the output capacitor and load by storage inductor l1, which means that d1 is part of the high-current return path.
mic4690 micrel mic4690 8 april 2005 applications information adjustable regulators adjustable regulators require a 1.23v feedback signal. rec- ommended voltage-divider resistor values for common out- put voltages are included in figure 1b. for other voltages, the resistor values can be determined using the following formulas: vv r1 r2 1 r1 r2 v v 1 v 1.23v out ref out ref ref =+ ? ? ? ? ? ? = ? ? ? ? ? ? ? =

!! " power #$ figure 1a. adjustable regulator circuit bill of material matrix v out r1 (1) r2 (1) v in c in d1 l1 c out i out 5.0v 3.01k 976 ? 6.8v-30v 22 f, 35v 2a, 40v 18 h 220 f, 10v see soa vishay-dale schotty sumida vishay-dale 595d226x0035d2t ss24 cdrh6d38-180ml 594d227x0010d2t micro commercial 5.0v 3.01k 976 ? 6.8v-14v 47 f, 20v 2a, 20v 18 h 100 f, 6.3v 1.0a vishay-dale schotty sumida vishay-dale 595d476x0020c2t ss22 cdrh6d38-180ml 595d107x06r3c2t micro commercial 3.3v 3.01k 1.78k 4.9v-14v 47 f, 20v 2a, 20v 15 h 120 f, 4.0v 1.0a vishay-dale schotty sumida vishay-dale 595d476x0020c2t ss22 cdrh6d38-150ml 595d127x0004c2t micro commercial 2.5v 3.01k 2.94k 4.25v-14v 47 f, 20v 2a, 20v 10 h 120 f, 4.0v 1.0a vishay-dale schotty sumida vishay-dale 595d476x0020c2t ss22 cdrh6d38-100ml 595d127x0004c2t micro commercial 1.8v 3.01k 6.49k 4.0v-14v 47 f, 20v 2a, 20v 10 h 120 f, 4.0v 1.0a vishay-dale schotty sumida vishay-dale 595d476x0020c2t ss22 cdrh6d38-100ml 595d127x0004c2t micro commercial note 1. all resistors 1% figure 1b. recommended components for common ouput voltages
april 2005 9 mic4690 mic4690 micrel when designing with the mic4690, it is a good practice to connect pins 5 through 8 to the largest ground plane that is practical for the specific design. checking the maximum junction temperature: for this example, with an output power (p out ) of 5w, (5v output at 1a maximum with v in = 12v) and 50 c maximum ambient temperature, what is the maximum junction tem- perature? referring to the ?ypical characteristics: 5v output effi- ciency?graph, read the efficiency ( ) for 1a output current at v in = 12v or perform you own measurement. = 75% the efficiency is used to determine how much of the output power (p out ) is dissipated in the regulator circuit (p d ). p= p p d out out ? p= 5w 0.75 5w d ? p d = 1.67w a worst-case rule of thumb is to assume that 80% of the total output power dissipation is in the mic4690 (p d(ic) ) and 20% is in the diode-inductor-capacitor circuit. p d(ic) = 0.8 p d p d(ic) = 0.8 1.67w p d(ic) = 1.336w calculate the worst-case junction temperature: t j = p d(ic) jc + (t c ?t a ) + t a(max) where: t j = mic4690 junction temperature p d(ic) = mic4690 power dissipation jc = junction-to-case thermal resistance. the jc for the mic4690? power-sop-8 is approximately 20 c/w. t c = ?in?temperature measurement taken at the entry point of pins 6 or 7 t a = ambient temperature t a(max) = maximum ambient operating temperature for the specific design. calculating the maximum junction temperature given a maximum ambient temperature of 50 c: t j = 1.336w 20 c/w + (63 c ?25 c) + 50 c t j = 114.72 c this value is within the allowable maximum operating junc- tion temperature of 125 c as listed in ?perating ratings. typical thermal shutdown is 160 c and is listed in ?lectrical characteristics. layout considerations layout is very important when designing any switching regu- lator. rapidly changing currents through the printed circuit board traces and stray inductance can generate voltage transients which can cause problems. ja jc ca ambient printed circuit board ground plane heat sink are a sop-8 figure 2. power sop-8 cross section thermal considerations the mic4690 superswitcher features the power-sop-8. this package has a standard 8-lead small-outline package profile, but with much higher power dissipation than a stan- dard sop-8. micrel's mic4690 superswitcher family are the first dc-to-dc converters to take full advantage of this package. the reason that the power sop-8 has higher power dissipa- tion (lower thermal resistance) is that pins 5 through 8 and the die-attach paddle are a single piece of metal. the die is attached to the paddle with thermally conductive adhesive. this provides a low thermal resistance path from the junction of the die to the ground pins. this design significantly im- proves package power dissipation by allowing excellent heat transfer through the ground leads to the printed circuit board. one limitation of the maximum output current on any mic4690 design is the junction-to-ambient thermal resistance ( ja ) of the design (package and ground plane). examining ja in more detail: ja = ( jc + ca ) where: jc = junction-to-case thermal resistance ca = case-to-ambient thermal resistance jc is a relatively constant 20 c/w for a power sop-8. ca is dependent on layout and is primarily governed by the connection of pins 5 though 8 to the ground plane. the purpose of the ground plane is to function as a heat sink. ja is ideally 63 c/w, but will vary depending on the size of the ground plane to which the power sop-8 is attached. determining ground-plane heat-sink area there are two methods of determining the minimum ground plane area required by the mic4690. quick method make sure that mic4690 pins 5 though 8 are connected to a ground plane with a minimum area of 6cm 2 . this ground plane should be as close to the mic4690 as possible. the area may be distributed in any shape around the package or on any pcb layer as long as there is good thermal contact to pins 5 though 8 . this ground plane area is more than sufficient for most designs.
mic4690 micrel mic4690 10 april 2005
! power sop-8 "#$% figure 5. critical traces for layout

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%& ' % ( ) * )" + , - , ./- % ,. )" + , /- , 0- , /0.1 %2 %3 %4 . 0 ( 3 2# 6!#4 )7"4# 44"" + !2"+"8 4 "9)7#4 !"# #!) !# figure 6a. evaluation board schematic diagram to minimize stray inductance and ground loops, keep trace lengths, indicated by the heavy lines in figure 5, as short as possible. for example, keep d1 close to pin 3 and pins 5 through 8, keep l1 away from sensitive node fb, and keep c in close to pin 2 and pins 5 though 8. see ?pplications information: thermal considerations?for ground plane lay- out. the feedback pin should be kept as far way from the switching elements (usually l1 and d1) as possible. a circuit with sample layouts are provided. see figures 6a though 6e. gerber files are available upon request.
april 2005 11 mic4690 mic4690 micrel abbreviated bill of material (critical components) reference part number manufacturer description qty c1 595d2260035d2t vishay sprague 1 22 f, 35v 1 ece-a1hfs470 panasonic 47 f, 50v, 8mm x 11.5mm tpsd226m035r0300 avx 2 22 f, 35v c2, c6 vj0805y104kxamb vishay vitramon 2 0.1 f 50v 2 c4 594d227x0010d2t vishay sprague 1 220 f, 10v 1 d1 ss24 micro commercial corp 3 schottky 2a, 40a 1 b240a diode inc l1 cdrh6d38-180mc sumida 4 18 h, 1.5a i sat 1 u1 mic4690bm micrel semiconductor 5 1a 200khz power-so-8 buck regulator 1 1 vishay dale, inc., tel: 1 877-847-4291, http://www.vishay.com 2 diodes inc, tel: (805) 446-4800, http://www.diodes.com 3 micro commercial corp., tel: (800) 346-3371 4 sumida, tel: (408) 982-9960, http://www.sumida.com 5 micrel, tel: (408) 944-0800, http://www.micrel.com printed circuit board layouts figure 6b. top-side silk screen figure 6c. top-side copper figure 6d. bottom-side silk screen figure 6e. bottom-side copper
mic4690 micrel mic4690 12 april 2005 package information 45 0 ? 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-lead sop (m) micrel, inc. 2180 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 web http://www.micrel.com the information furnished by micrel in this data sheet is believed to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and specifications at any time without notification to the customer. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intend ed for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant inj ury to the user. a purchaser? use or sale of micrel products for use in life support appliances, devices or systems is at purchaser? own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ?2005 micrel, incorporated.

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