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april 2005 1 m9999-042205 mic2288 micrel, inc. mic2288 1a 1 .2mhz pwm boost converter in thin sot-23 and 2 2 mlf? general description the mic2288 is a 1.2mhz pwm, dc/dc boost switching regulator available in low-profile thin sot-23 and 2mm 2mm mlf? package options. high power density is achieved with the mic2288s internal 34v/1a switch, allow- ing it to power large loads in a tiny footprint. the mic2288 implements a constant frequency, 1.2mhz pwm, current mode control scheme with internal compensa- tion that offers excellent transient response and output regu - lation performance. the high frequency operation saves board space by allowing small, low-profile, external compo- nents. the fixed frequency pwm topology also reduces spurious switching noise and ripple to the input power source. the mic2288 is available in a low-profile thin sot-23-5 package and a 2mm 2mm mlf?-8 leadless package. the 2mm 2mm mlf?-8 package option has an output over- voltage protection feature. the mic2288 has a junction temperature range of C40 c to +125 c. all support documentation can be found on micrels web site at www.micrel.com. t ypical application 2 l1 10 h r2 r1 3 1 4 5 mic2288bd5 vin 1-cellli ion v out 15v en sw fb gnd v in c12.2 f c210 f 2mm 2mm mlf? boost regulator features ?2 .5v to 10v input voltage range ? output voltage adjustable to 34v ? over 1a switch current ?1 .2mhz pwm operation ?s table with ceramic capacitors ? high-efficiency ? <1% line and load regulation ? low input and output ripple ?<1 a shutdown current ? uvlo ? output overvoltage protection (mic2288bml) ? over temperature shutdown ? thin sot-23-5 package option ? 2mm 2mm leadless mlf?-8 package option ? C40 c to +125 c junction temperature range applications ?o rganic el power supply ? tft-lcd bias supply ? 12v supply for dsl applications ? multi-output dc/dc converters ? positive and negative output regulators ? sepic converters micrel, inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408) 474-1000 ? http ://www.mi crel.com mlf and micro leadframe are trademarks of amkor technology, inc. 60 65 70 75 80 85 90 00 . 0 50 .1 0.15 0.2 efficiency (%) load (a) 15v out efficiency v in = 4.2v v in = 3.2v v in = 3.6v downloaded from: http:///
mic2288 micrel, inc. m9999-042205 2 april 2005 pin description pin number pin number tsot-23-5 2 2 mlf?-8 pin name pin function 17 sw switch node (input): internal power bipolar collector. 2 gnd ground (return): ground. 36 fb feedback (input): 1.24v output voltage sense node. v out = 1.24v 1 r1 r2 + ? ? ? ? ? ? 43 en enable (input): logic high enables regulator. logic low shut s down regulator. 52 vin supply (input): 2.5v to 10v input voltage. 1 ovp output overvoltage protection (input): tie this pin to v out to clamp the output voltage to 34v maximum in fault conditions. tie this pin to ground if ovp function is not required. 5n c no connect: no internal connection to die. 4 agnd analog ground. 8 pgnd power ground. ep gnd exposed backside pad. pin configuration fb gnd en vin sw 3 1 5 2 4 tsot-23-5 (d5) ovp vin en agnd pgnd sw fb nc 1 2 3 4 8 7 6 5 ep 8-pin mlf? (ml) (top view) fused lead frame ordering information marking output overvoltage junction part number code voltage protection temp. range package lead fini sh mic2288bd5 shaa adjustable C C40 c to 125 c thin sot-23-5 standard mic2288yd5 shaa adjustable C C40 c to 125 c thin sot-23-5 lead free mic2288bml sja adjustable 34v C40 c to 125 c2 2 mlf?-8 standard mic2288yml sja adjustable 34v C40 c to 125 c2 2 mlf?-8 lead free downloaded from: http:///
april 2005 3 m9999-042205 mic2288 micrel, inc. absolute maximum ratings (1) supply voltage (v in ) .................................................. ... 12v switch voltage (v sw ) ..................................... C0.3v to 34v enable pin voltage (v en ) ................................... C0.3 to v in fb voltage (v fb ) ................................................... .......... 6v switch current (i sw ) ................................................... .... 2a storage temperature (t s ) ....................... C65 c to +150 c esd rating (3) ................................................... ............. 2kv operating ratings (2) supply voltage (v in ) ........................................ 2.5v to 10v junction temperature range (t j ) ........... C40 c to +125 c package thermal impedance 2mm 2mm mlf?-8 ( ja ) ................................. 93 c/w thin sot-23-5 ( ja ) .......................................... 256 c/w electrical characteristics (4) t a = 25 c, v in = v en = 3.6v, v out = 10v, i out = 20ma, unless otherwise noted. bold values indicate C40 c t j 125 c. symbol parameter condition min typ max units v in supply voltage range 2.5 10 v v uvlo under voltage lockout 1.8 2.1 2.4 v i vin quiescent current v fb = 2v, (not switching) 2.8 5 ma i sd shutdown current v en = 0v (5) 0.1 1 a v fb feedback voltage ( 1%) 1.227 1.24 1.252 v ( 2%) (over temp) 1.215 1.265 v i fb feedback input current v fb = 1.24v C450 na line regulation 3v v in 5v 0.1 1 % load regulation 5ma i out 40ma 0.2 % d max maximum duty cycle 85 90 % i sw switch current limit 1.2 a v sw switch saturation voltage i sw = 1a 550 mv i sw switch leakage current v en = 0v, v sw = 10v 0.01 5 a v en enable threshold turn on 1.5 v turn off 0.4 v i en enable pin current v en = 10v 20 40 a f sw oscillator frequency 1.05 1.2 1.35 mhz v ovp output overvoltage protection mic2288 mlf? package option only 3 0 32 34 v t j overtemperature 150 c threshold shutdown hysteresis 10 c notes: 1. absolute maximum ratings indicate limits beyond which damage to the component may occur. electrical specifications do not apply wh en operating the device outside of its operating ratings. the maximum allow able power dissipation is a function of the maximum junction temperature, t j (max), the junction-to-ambient thermal resistance, ja , and the ambient temperature, t a . the maximum allowable power dissipation will result in excessi ve die temperature, and the regulator will go into thermal shu tdown. 2. this device is not guaranteed to operate beyond its specifi ed operating rating. 3. ic devices are inherently esd sensitive. handling precautions re quired. human body model rating: 1.5k in series with 100pf. 4. specification for packaged product only. 5. i sd = i vin . downloaded from: http:///
mic2288 micrel, inc. m9999-042205 4 april 2005 t ypical characteristics 75 77 79 81 83 85 87 89 91 0255 075 100 125 150 efficiency (%) output current (ma) efficiency at v out = 12v v in = 4.2v v in = 3.6v v in = 3.3v 11.8 11.85 11.9 11.95 12 12.05 12.1 12.15 12.2 0255 075 100 125 150 output voltage (v) load (ma) load re g ulation v in = 3.6v 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30 -40 -20 0 20 40 60 80 100 120 feedback voltage (v) temperature ( c) feedback voltage vs. tem p erature 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2.5 4 5.5 7 8.5 10 current limit (a) supply voltage (v) current limit vs. su pp l y current 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -40 -20 0 20 40 60 80 100 120 current limit (a) temperature ( c) current limit vs. tem p erature 0 50 100 150 200 250 300 2.5 4 5.5 7 8.5 10 switch saturation voltage (mv) supply voltage (v) switch saturation vs. su pp l y volta g e i sw = 500ma 0 100 200 300 400 500 600 700 0 200 400 600 800 1000 switch saturation voltage (mv) switch current (ma) switch saturation vs. current v in = 3.6v 0 100 200 300 400 500 600 700 -40 -20 0 20 40 60 80 100 120 switch saturation voltage (mv) temperature ( c) switch saturation vs. temperature v in = 3.6v i sw = 500ma 0.8 0.9 1.0 1.1 1.2 1.3 1.4 -40 -20 0 20 40 60 80 100 120 frequency (mhz) temperature ( c) frequency vs. tem p erature 80 82 84 86 88 90 92 94 96 98 100 2.5 4 5.5 7 8.5 10 maximum duty cycle (%) supply voltage (v) maximum duty cycle vs. supply voltage 85 87 89 91 93 95 97 99 -40 -20 0 20 40 60 80 100 120 maximum duty cycle (%) temperature ( c) maximum duty cycle vs. temperature v in = 3.6v 0 100 200 300 400 500 600 700 -40 -20 0 20 40 60 80 100 120 feedback current (na) temperature ( c) fb pin current vs. tem p erature downloaded from: http:///
april 2005 5 m9999-042205 mic2288 micrel, inc. function characteristics enable characteristics time (400s/div) output voltage (5v/div) enable voltage (2v/div) 3.6v in 12v out 150ma load output voltage enable voltage line transient response time (400 s/div) output voltage (1mv/div) ac-coupled input voltage (2v/div) 4.2v 3.2v 12v out 150ma load load transient response time (400 s/div) output voltage (100mv/div) ac-coupled load current (100ma/div) 10ma 150ma 3.6v in 12v out c out = 10 f switching waveforms time (400ns/div) output voltage (50mv/div) inductor current (500ma/div) switch saturation (5v/div) v sw output voltage 3.6v in 12v out 150ma inductor current(10 h) downloaded from: http:///
mic2288 micrel, inc. m9999-042205 6 april 2005 functional description the mic2288 is a constant frequency, pwm current mode boost regulator. the block diagram is shown in figure 1. the mic2288 is composed of an oscillator, slope compensation ramp generator, current amplifier, g m error amplifier, pwm generator, and a 1a bipolar output transistor. the oscillator generates a 1.2mhz clock. the clocks two functions are to trigger the pwm generator that turns on the output transistor, and to reset the slope compensation ramp generator. the current amplifier is used to measure the switch current by amplifying the voltage signal from the internal sense resistor. the output of the current amplifier is summed with the outpu t of the slope compensation ramp generator. this summed current-loop signal is fed to one of the inputs of the pwm generator. functional diagram gnd ca pwm generator ramp generator 1.2mhz oscillator sw en fb ovp* vin 1.24v * ovp available on mlf tm package option only. g m ovp* v r e f figure 1. mic2288 block diagram the g m error amplifier measures the feedback voltage through the external feedback resistors and amplifies the error be- tween the detected signal and the 1.24v reference voltage. the output of the g m error amplifier provides the voltage-loop signal that is fed to the other input of the pwm generato r. when the current-loop signal exceeds the voltage-loop sig- nal, the pwm generator turns off the bipolar output transisto r. the next clock period initiates the next switching cycle, maintaining the constant frequency current-mode pwm con- trol. downloaded from: http:///
april 2005 7 m9999-042205 mic2288 micrel, inc. applications information dc-to-dc pwm boost conversion the mic2288 is a constant-frequency boost converter. it operates by taking a dc input voltage and regulating a hi gher dc output voltage. figure 2 shows a typical circuit. boost regulation is achieved by turning on an internal switch, whi ch draws current through the inductor (l1). when the switch turns off, the inductors magnetic field collapses, causing the current to be discharged into the output capacitor through an external schottky diode (d1). voltage regulation is achieved by modulating the pulse width or pulse-width modulation (pwm). l1 10 h c210 f r2 r1 mic2288bml vin v in v out en sw fb gnd gnd ovp gnd c1 2.2 f d1 figure 2. typical application circuit duty cycle considerations duty cycle refers to the switch on-to-off time ratio and can be calculated as follows for a boost regulator: d1 v v in out = ? the duty cycle required for voltage conversion should be less than the maximum duty cycle of 85%. also, in light load conditions where the input voltage is close to the output voltage, the minimum duty cycle can cause pulse skipping. this is due to the energy stored in the inductor causing the output to overshoot slightly over the regulated output volta ge. during the next cycle, the error amplifier detects the output a s being high and skips the following pulse. this effect can be reduced by increasing the minimum load or by increasing the inductor value. increasing the inductor value reduces peak current, which in turn reduces energy transfer in each cycle. overvoltage protection for the mlf? package option, there is an overvoltage protection function. if the feedback resistors are discon- nected from the circuit or the feedback pin is shorted to ground, the feedback pin will fall to ground potential. this will cause the mic2288 to switch at full duty cycle in an attempt to maintain the feedback voltage. as a result, the output voltage will climb out of control. this may cause the switch node voltage to exceed its maximum voltage rating, possibly damaging the ic and the external components. to ensure the highest level of protection, the mic2288 ovp pin will shut the switch off when an overvoltage condition is detected, saving itself and other sensitive circuitry downstream. component selection inductor inductor selection is a balance between efficiency, stability, cost, size, and rated current. for most applications a 10 h is the recommended inductor value. it is usually a good balance between these considerations. larger inductance values reduce the peak-to-peak ripple current, affecting efficiency. this has the effect of reducing both the dc losses and the transition losses. there is also a secondary effect of an inductors dc resistance (dcr). the dcr of an inductor will be higher for more inductance in th e same package size. this is due to the longer windings required for an increase in inductance. since the majority of input current (minus the mic2288 operating current) is passed through the inductor, higher dcr inductors will reduce effi- ciency. to maintain stability, increasing inductor size will have to b e met with an increase in output capacitance. this is due to t he unavoidable right half plane zero effect for the continuou s current boost converter topology. the frequency at which the right half plane zero occurs can be calculated as follows: f v vli 2 rhpz in out out = 2 the right half plane zero has the undesirable effect of increasing gain, while decreasing phase. this requires that the loop gain is rolled off before this has significant ef fect on the total loop response. this can be accomplished by either reducing inductance (increasing rhpz frequency) or in- creasing the output capacitor value (decreasing loop gain). output capacitor output capacitor selection is also a trade-off between perfor- mance, size, and cost. increasing output capacitance will lead to an improved transient response, but also an increase in size and cost. x5r or x7r dielectric ceramic capacitors are recommended for designs with the mic2288. y5v values may be used but to offset their tolerance over temperature, more capacitance is required. the following table shows the recommended ceramic (x5r) output capacitor value vs. output voltage. output voltage recomended output capacitance <6v 22 f <16v 10 f <34v 4.7 f table 1. output capacitor selection diode selection the mic2288 requires an external diode for operation. a schottky diode is recommended for most applications due to their lower forward voltage drop and reverse recovery time. ensure the diode selected can deliver the peak inductor current and the maximum reverse voltage is rated greater than the output voltage. downloaded from: http:///
mic2288 micrel, inc. m9999-042205 8 april 2005 input capacitor a minimum 1 f ceramic capacitor is recommended for designing with the mic2288. increasing input capacitance will improve performance and greater noise immunity on the source. the input capacitor should be as close as possible to the inductor and the mic2288, with short traces for good noise performance. feedback resistors the mic2288 utilizes a feedback pin to compare the output to an internal reference. the output voltage is adjusted b y selecting the appropriate feedback resistor network values. the r2 resistor value must be less than or equal to 5k ? (r2 5k ? ).the desired output voltage can be calculated as follows: vv r1 r2 1 out ref =+ ? ? ? ? ? ? where v ref is equal to 1.24v. downloaded from: http:///
april 2005 9 m9999-042205 mic2288 micrel, inc. application circuits l1 4.7 h c222 f 6.3v r21.87k r15.62k mic2288bml vin v in 3v to 4.2v v out 5v @ 400ma en sw fb gnd gnd ovp gnd c1 4.7 f 6.3v d1 c1 4.7 f, 6.3v, 0805 x5r ceramic capacitor 08056d475mat avx c2 22 f, 6.3v, 0805 x5r ceramic capacitor 12066d226mat avx d1 1a, 40v schotty diode mbrm140t3 on semi. l1 4.7 h, 650ma inductor lqh32cn4r7m11 murata figure 3. 3.3v in to 5v out @ 400ma l1 10 h c210 f 16v r25k r131.6k mic2288bml vin v in 3v to 4.2v v out 9v @ 180ma en sw fb gnd gnd ovp gnd c1 2.2 f 10v d1 c1 2.2 f, 10v, 0805 x5r ceramic capacitor 08052d225kat avx c2 10 f, 16v, 1206 x5r ceramic capacitor 1206yd106mat avx d1 1a, 40v schotty diode mbrm140t3 on semi. l1 10 h, 650ma inductor lqh43cn100k03 murata figure 4. 3.3v in C 4.2v in to 9v out @ 180ma l1 10 h c210 f 16v r25k r142.3k mic2288bml vin v in 3v to 4.2v v out 12v @ 100ma en sw fb gnd gnd ovp gnd c1 2.2 f 10v d1 c1 2.2 f, 10v, 0805 x5r ceramic capacitor 08052d225kat avx c2 10 f, 16v, 1206 x5r ceramic capacitor 1206yd106mat avx d1 1a, 40v schotty diode mbrm140t3 on semi. l1 10 h, 650ma inductor lqh43cn100k03 murata figure 5. 3.3v in C 4.2v in to 12v out @ 100ma l1 10 h c210 f 16v r25k r154.9k mic2288bml vin v in 3v to 4.2v v out 15v @ 100ma en sw fb gnd gnd ovp gnd c1 2.2 f 10v d1 c1 2.2 f, 10v, 0805 x5r ceramic capacitor 08052d225kat avx c2 10 f, 16v, 1206 x5r ceramic capacitor 1206yd106mat avx d1 1a, 40v schotty diode mbrm140t3 on semi. l1 10 h, 650ma inductor lqh43cn100k03 murata figure 6. 3.3v in C 4.2v in to 15v out @ 100ma l1 10 h c24.7 f 25v r21k r118.2k mic2288bml vin v in 3v to 4.2v v out 24v @ 50ma en sw fb gnd gnd ovp gnd c1 2.2 f 10v d1 c1 2.2 f, 10v, 0805 x5r ceramic capacitor 08052d225kat avx c2 4.7 f, 25v, 1206 x5r ceramic capacitor 12063d475mat avx d1 1a, 40v schotty diode mbrm140t3 on semi. l1 10 h, 650ma inductor lqh43cn100k03 murata figure 7. 3.3v in C 4.2v in to 24v out @ 50ma l1 10 h c210 f 16v r25k r131.6k mic2288bml vin v in 5v v out 9v @ 330ma en sw fb gnd gnd ovp gnd c1 2.2 f 10v d1 c1 2.2 f, 10v, 0805 x5r ceramic capacitor 08052d225kat avx c2 10 f, 16v, 1206 x5r ceramic capacitor 1206yd106mat avx d1 1a, 40v schotty diode mbrm140t3 on semi. l1 10 h, 650ma inductor lqh43cn100k03 murata figure 8. 5v in to 9v out @ 330ma downloaded from: http:///
mic2288 micrel, inc. m9999-042205 10 april 2005 l1 10 h c210 f 16v r25k r143.2k mic2288bml vin v in 5v v out 12v @ 250ma en sw fb gnd gnd ovp gnd c1 2.2 f 10v d1 c1 2.2 f, 10v, 0805 x5r ceramic capacitor 08052d225kat avx c2 10 f, 16v, 1206 x5r ceramic capacitor 1206yd106mat avx d1 1a, 40v schotty diode mbrm140t3 on semi. l1 10 h, 650ma inductor lqh43cn100k03 murata figure 9. 5v in to 12v out @ 250ma l1 10 h c24.7 f 25v r21k r118.2k mic2288bml vin v in 5v v out 24v @ 80ma en sw fb gnd gnd ovp gnd c1 2.2 f 10v d1 c1 2.2 f, 10v, 0805 x5r ceramic capacitor 08052d225kat avx c2 4.7 f, 25v, 1206 x5r ceramic capacitor 12066d475mat avx d1 1a, 40v schotty diode mbrm140t3 on semi. l1 10 h, 650ma inductor lqh32cn4r7m11 murata figure 10. 5v in to 24v out @ 80ma downloaded from: http:///
april 2005 11 m9999-042205 mic2288 micrel, inc. package information all dimensions are in millimeters 5-pin tsot (d5) 8-pin mlf? (ml) 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 this information furnished by micrel in this data sheet is beli eved to be accurate and reliable. however no responsibility is assumed by micrel for its use. micrel reserves the right to change circuitry and specifications at an y 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 malfunction of a product can reasonably be expected to result in personal injury. life suppo rt devices or systems are devices or systems that (a) are intended for surgica l implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant in jury to the user. a purchasers use or sale of micrel products for use in life support appliances, devices or systems is a purchasers own risk and purchaser agrees to fully ind emnify micrel for any damages resulting from such use or sale. ? 2004 micrel, incorporated. downloaded from: http:///

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