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MIC2285A 8mhz pwm synchronous buck regulator with ldo standby mode lowq is a registered tr ademark of micrel, inc mlf and micro leadframe are registered trademarks of amkor technology, inc. micrel, inc ? 2180 fortune drive ? san jose, ca 95131 ? usa ? te l +1 (408) 944-0800 ? fax +1 (408) 474-1000 ? http://www.micrel .com august 2007 m9999-083107-b general description the micrel MIC2285A is a high efficiency 8mhz pwm synchronous buck (st ep-down) regulator that features a lowq ? ldo standby mode that draws only 20a of quiescent current. the MIC2285A allows an ultra-low noise, small size, and high efficiency solution for portable power applications. in pwm mode, the MIC2285A operates with a constant frequency 8mhz pwm control. under light load conditions, such as in system sleep or standby modes, the pwm switching operation can be disabled to reduce switching losses. in this light load lowq ? mode, the ldo maintains the output voltage and draws only 18a of quiescent current. the ldo mode of operation saves battery life while not introducing spurious noise and high ripple as experienced with pulse skipping or bursting mode regulators. the MIC2285A operates from 2.7v to 5.5v input and features internal power mosfets that can supply up to 600ma output current in pwm mode. it can operate with a maximum duty cycle of 100% for use in low-dropout conditions. the MIC2285A is available in the 10-pin 2mm x 2mm thin mlf ? package with a junction operating range from ?40 c to +125 c. data sheets and support documentation can be found on micrel?s web site at: www.micrel.com. features ? 2.7 to 5.5v supply/input voltage ? light load lowq ? ldo mode ? 20a quiescent current ? low noise, 75vrms ? 8mhz pwm mode ? output current to 600ma ? >90% efficiency ? 100% maximum duty cycle ? adjustable output voltage option down to 1v ? fixed output voltage options available ? ultra-fast transient response ? requires only a 0.47h inductor ? enables sub 0.55mm profile solution ? fully integrated mosfet switches ? micropower shutdown ? thermal shutdown and current limit protection ? 10-pin 2mm x 2mm x 0.55mm mlf ? package ? ?40 c to +125 c junction temperature range applications ? cellular phones ? pdas ? usb peripherals ____________________________________________________________________________________________________ typical application adjustable output buck regulator with lowq ? mode 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 600 output current (ma) 2.5v out efficiency v in =3.2v v in =3.6v v in =4.2v
micrel, inc. MIC2285A august 2007 2 m9999-083107-b ordering information part number marking output voltage* junction temperature range package lead finish MIC2285Aymt wpa adj. ?40 to +125c 10-pin 2x2 thin mlf ? pb-free note * for other voltage options available, please contact micrel marketing for details. mlf? is a green rohs compliant package. lead finish is nipdau. mold compound is halogen free. pin configuration fb en 5 1 a gnd ldo bias avin 10 pgnd sw vin lowq 9 8 7 2 3 4 6 10-pin 2mm x 2mm thin mlf ? (mt) pin description pin number pin name pin function 1 agnd analog (signal) ground. 2 ldo ldo output (output): connect to v out for ldo mode operation. 3 bias internal circuit bias supply. must be decoupled to signal ground with a 0.1f capacitor and should not be loaded. 4 avin analog supply voltage (input): supply vo ltage for the analog control circuitry and ldo input power. requires bypass capacitor to gnd. 5 fb feedback. input to the error amplifier. for the adjustable option, connect to the external resistor divider network to se t the output voltage. for fixed output voltage options, connect to v out and an internal resistor network sets the output voltage. 6 en enable (input). logic low will shut do wn the device, reducing the quiescent current to less than 5a. 7 _____ lowq enable ldo mode (input): logic low en ables the internal ldo and disables the pwm operation. logic high enables the pwm mode and disables the ldo mode. 8 vin supply voltage (input): supply voltage for the internal switches and drivers. 9 sw switch (output): internal power mosfet output switches. 10 pgnd power ground.
micrel, inc. MIC2285A august 2007 3 m9999-083107-b absolute maximum ratings (1) supply voltage (v in ) ............................................ +6v output switch voltage (v sw ) ............................... +6v output switch current (i sw ) ................................... 2a logic input voltage (v en ,v lowq ) ..............?0.3v to v in storage temperature (t s )............... ?60c to +150c esd rating (3) ....................................................... 3kv operating ratings (2) supply voltage (v in )............................+2.7v to +5.5v logic input voltage (v en ,v lowq ) ............. ?0.3v to v in junction temperature (t j ) .............. ?40c to +125c junction thermal resistance 2x2 mlf-10l ( ja ) ................................... 60c/w electrical characteristics (4) v in = v en = v lowq =3.6v; l = 0.47h; c out = 10f; t a = 25c, unless noted. bold values indicate ?40c< t j < +125c parameter condition min typ max units supply voltage range 2.7 5.5 v under-voltage lockout threshold (turn-on) 2.45 2.55 2.65 v uvlo hysteresis 100 mv quiescent current, pwm mode v fb = 0.9 * v nom (not switching) 790 900 a quiescent current, ldo mode v lowq = 0v;i out = 0ma 20 29 a shutdown current v en = 0v 0.01 5 a [adjustable] feedback voltage 1% 2% (over temperature) 0.99 0.98 1 1.01 1.02 v v [fixed output] voltages nominal v out tolerance ?1 ?2 +1 +2 % % fb pin input current 1 na current limit in pwm mode v fb = 0.9 * v nom 0.75 1 1.85 a output voltage line regulation v out > 2v; v in = v out +300mv to 5.5v; i load = 100ma v out < 2v; v in = 2.7v to 5.5v; i load = 100ma 0.13 % output voltage load regulation, pwm mode 20ma < i load < 300ma 0.2 0.8 % output voltage load regulation, ldo mode 100a < i load < 50ma v lowq = 0v 0.5 1 % maximum duty cycle v fb 0.4v 100 % pwm switch on- resistance i sw = 50ma v fb = 0.7v fb_nom (high side switch) i sw = -50ma v fb = 1.1v fb_nom (low side switch) 0.4 0.4 ? ? oscillator frequency 7.2 8 8.8 mhz lowq threshold voltage 0.5 0.85 1.3 v lowq input current 0.1 2 a enable threshold 0.5 0.85 1.3 v enable input current 0.1 2 a ldo dropout voltage i out = 50ma note 5 110 mv
micrel, inc. MIC2285A august 2007 4 m9999-083107-b parameter condition min typ max units output voltage noise lowq = 0v; c out = 10 f, 10hz to 100khz 75 vrms ldo current limit lowq = 0v; v out = 0v (ldo mode) 60 120 ma over-temperature shutdown 160 c over-temperature hysteresis 20 c notes 1. exceeding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. devices are esd sensitive. handling pr ecautions recommended. human body model: 1.5k ? in series with 100pf. 4. specification for packaged product only. 5. dropout voltage is defined as the input-to-output differential at which the output voltage drops 2% below its nominal value that is initially measured at a 1v differential. for outputs below 2.7v, the dropout voltage is the input-to-output voltage diff erential with a minimum input voltage of 2.7v.
micrel, inc. MIC2285A august 2007 5 m9999-083107-b typical characteri stics ? pwm mode 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 600 output current (ma) 2.5v out efficiency v in =3.2v v in =3.6v v in =4.2v 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 600 output current (ma) v in =3.2v v in =3.6v v in =4.2v 1.8v out efficiency 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 600 output current (ma) 1.5v out efficiency v in =3.2v v in =3.6v v in =4.2v 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 600 output current (ma) 1.2v out efficiency v in =3.2v v in =3.6v v in =4.2v 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 600 output current (ma) 1.0v out efficiency v in =3.2v v in =3.6v v in =4.2v 0 100 200 300 400 500 600 output current (ma) 0.990 load regulation 0.994 0.998 1.002 1.006 1.010 1.014 1.018 v in =3.6v lowq=v in 600 700 800 900 1000 1100 2.7 input voltage (v) quiescent current vs. input voltage 3.1 3.5 3.9 4.3 4.7 5.1 5.5 7.0 7.5 8.0 8.5 9.0 2.7 input voltage (v) frequency vs. input voltage 3.1 3.5 3.9 4.3 4.7 5.1 5.5 0 200 400 600 800 1000 1200 2.7 3.4 4.1 4.8 5.5 current limit (ma) supply voltage (v) peak current limit vs. supply voltage lowq = v in 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 2.7 3.4 4.1 4.8 5.5 enable threshold (v) supply voltage (v) enable threshold vs. supply voltage lowq = v in
micrel, inc. MIC2285A august 2007 6 m9999-083107-b typical characteristics - ldo mode 0 20 40 60 80 100 120 140 2.7 3.4 4.1 4.8 5.5 current limit (ma) supply voltage (v) current limit vs. supply voltage lowq = 0v 0 20 40 60 80 100 120 140 160 -40 -20 0 20 40 60 80 100 120 dropout voltage (mv) temperature (c) dropout voltage vs. temperature v out = 3.3v i out = 50ma lowq = 0v 0 10 20 30 40 50 60 70 80 -40 -20 0 20 40 60 80 100 120 dropout voltage (mv) temperature (c) dropout voltage vs. temperature v out = 3.3v i out = 25ma lowq = 0v 0 5 10 15 20 25 30 35 40 -40 -20 0 20 40 60 80 100 120 dropout voltage (mv) temperature (c) dropout voltage vs. temperature v out = 3.3v i out = 10ma lowq = 0v 0 1 2 3 4 5 6 7 8 9 -40 -20 0 20 40 60 80 100 120 dropout voltage (mv) temperature (c) dropout voltage vs. temperature v out = 3.3v i out = 1ma lowq = 0v 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 2.7 3.4 4.1 4.8 5.5 enable threshold (v) supply voltage (v) enable threshold voltage vs. supply voltage lowq = 0v
micrel, inc. MIC2285A august 2007 7 m9999-083107-b typical characteristics ? ldo mode (cont.) 15 16 17 18 19 20 21 22 23 24 25 0 20406080100 quiescent current (a) output current (ma) quiescent current vs. output current v in =3.6v lowq = 0v 1.764 1.773 1.782 1.791 1.8 1.809 1.818 1.827 1.836 0 20406080100 output voltage (v) output current (ma) output voltage vs. output current v in =3.6v v out =1.8v lowq = 0v
micrel, inc. MIC2285A august 2007 8 m9999-083107-b functional diagram MIC2285A block diagram
micrel, inc. MIC2285A august 2007 9 m9999-083107-b functional characteristics load transient pwm mode ac coupled (50mv/div) output current (100ma/div) time (20s/div) c out = 4.7f output volta g e 10ma load transient ldo mode ac coupled (50mv/div) output current (20ma/div) time (20s/div) c out = 4.7f output volta g e 10ma enable transient pwm mode output volta g e (1v/div) enable (2v/div) time (40s/div) c out = 4.7f 0v 0v enable transient ldo mode output voltage (1v/div) enable (2v/div) time (40s/div) c out = 4.7f 0v 0v
micrel, inc. MIC2285A august 2007 10 m9999-083107-b functional description vin vin provides power to the mosfets for the switch mode regulator section, along with the current limiting sensing. due to the high switching speeds, a 1f capacitor is recommended close to vin and the power ground (pgnd) pin for bypassing. please refer to layout recommendations. avin analog v in (avin) provides power to the ldo section. avin and vin mu st be tied together. careful layout should be considered to ensure high frequency switching noise caused by vin is reduced before reaching avin. ldo the ldo pin is the output of the linear regulator and should be connected to the output. in lowq mode (lowq<1.5v), the ldo prov ides the output voltage. in pwm mode (lowq>1.5v), the ldo pin is high impedance. en the enable pin provides a l ogic level control of the output. in the off state, supply current of the device is greatly reduced (typically <1a). also, in the off state, the output drive is placed in a "tri-stated" condition, where both t he high side p-channel mosfet and the low-side n-channel are in an ?off? or non-conducting state. do not drive the enable pin above the supply voltage. lowq the lowq pin provides a logic level control between the internal pwm mode and the low noise linear regulator mode. with lowq pulled low (<0.5v), quiescent current of the device is greatly reduced by switching to a low noise linear regulator mode that has a typical i q of 20a. in linear (ldo) mode, the output can deliver 60ma of current to the output. by placing lowq high (>1.5v), this transitions the device into a constant frequency pwm buck regulator mode. this allows the device the ability to efficiently de liver up to 500ma of output current at the same output voltage. bias the bias pin supplies the power to the internal power to the control and reference circuitry. the bias is powered from the input voltage through an rc lowpass filter. the rc lowpas s filter frequency must be ()() 100nf 20.5 ? 2 1 . fb the feedback pin (fb) provides the control path to control the output. for adjus table versions, a resistor divider connecting the feedbac k to the output is used to adjust the desired output voltage. the output voltage is calculated as follows: v out = v ref r1 r2 + 1 ? ? ? ? ? ? where v ref is equal to 1.0v. a feedforward capacitor is recommended for most designs using the adjusta ble output voltage option. to reduce battery current draw, a 100k feedback resistor is recommended from the output to the fb pin (r1). also, a feedforward capacitor should be connected between the output and feedback (across r1). the large resistor value and the parasitic capacitance of the fb pin can cause a high frequency pole that can redu ce the overall system phase margin. by placing a feedforward capacitor, these effects can be signific antly reduced. typically, an 82pf small ceramic capacitor is recommended. sw the switch (sw) pin connects directly to the inductor and provides the switching current necessary to operate in pwm mode. due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes. pgnd power ground (pgnd) is the ground path for the high current pwm mode. the current loop for the power ground should be as small as possible and separate from the analog ground (agnd) loop. refer to the layout considerations for more details. agnd signal ground (agnd) is the ground path for the biasing and control circuitry. the current loop for the signal ground should be separate from the power ground (pgnd) loop. refer to the layout considerations for more details.
micrel, inc. MIC2285A august 2007 11 m9999-083107-b applications information the MIC2285A is a 500ma pwm power supply that utilizes a lowq light load mode to maximize battery efficiency in light load cond itions. this is achieved with a lowq control pin that when pulled low, shuts down all the biasing and drive current for the pwm regulator, drawing only 18a of operating current. this allows the output to be regulated through the ldo output, capable of pr oviding 60ma of output current. this method has the advantage of producing a clean, low current, ultra-low noise output in lowq mode. during lowq mode, the sw node becomes high impedance, blocking current flow. other methods of reducing quiescent current, such as pulse frequency modulation (pfm), or bursting techniques, create large amplitude, low frequency ripple voltages that can be detrimental to system operation. when more than 60ma is required, the lowq pin can be forced high, causing the MIC2285A to enter pwm mode. in this case, the ldo output makes a "hand-off" to the pwm regul ator with virtually no variation in output voltag e. the ldo output then turns off allowing up to 600ma of current to be efficiently supplied through the pwm output to the load. input capacitor a minimum 1f ceramic is recommended on the vin pin for bypassing. x5r or x7r dielectrics are recommended for the input capacitor. y5v dielectrics lose most of their capacitance over temperature and are therefore, not recommended. a minimum 1f is recommended close to the vin and pgnd pins for high frequency filtering. smaller case size capacitors are recommended due to their lower esr and esl. please refer to layout recommendation section of data sheet for proper layout of the input capacitor. output capacitor the MIC2285A is optimized for a 10f output capacitor. a larger value can be used to improve transient response. the MIC2285A utilizes type iii internal compensation and ut ilizes an internal high frequency zero to compensate for the double pole roll off of the lc filter. fo r this reason, larger output capacitors can create in stabilities. x5r or x7r dielectrics are recommended for the output capacitor. y5v dielectrics lose most of their capacitance over temperature and are therefore, not recommended. in addition to a 10f, a small 10nf is recommended close to the load for high fr equency filtering. smaller case size capacitors are recommended due to their lower esr and esl. inductor selection the MIC2285A is designed for use with a 0.47h inductor. proper selection should ensure that the inductor can handle the maximum average and peak currents required by the load. maximum current ratings of the inductor are generally given in two methods; permissible dc current and saturation current. permissible dc current can be rated either for a 40c temperature rise or a 10% to 20% loss in inductance. ensure that the inductor selected can handle the maximum operating current. when saturation current is specifi ed, make sure that there is enough margin that the peak current will not saturate the inductor. peak inductor current can be calculated as follows: l f 2 v v 1 v i i in out out out pk ? ? ? ? ? ? ? ? ? + =
micrel, inc. MIC2285A august 2007 12 m9999-083107-b layout recommendation top bottom note the above figures demonstrate the recommended lay out for the MIC2285A adjustable option.
micrel, inc. MIC2285A august 2007 13 m9999-083107-b adjustable output bill of materials item part number manufacturer description qty 06036d105mat2 avx (1) c1 grm185r60j105ke21d murata (2) 1f ceramic capacitor x5r, 6.3v 0603 1 0201zd103mat2 avx (1) c2 grm033r10j103ka01d murata (2) 10nf ceramic capacitor, 6.3v 0201 1 c3 vj0402a101kxaa vishay (3) 100pf ceramic capacitor 1 avx (1) c4 murata (2) 10f ceramic capacitor x5r, 6.3v 0603 1 lqm21pnr47m00 murata (2) 0.47h inductor, 120m ? 2.0mm x 1.25mm x 0.5mm l1 murata (2) 0.47h inductor, 97m ? 3.2mm x 2.5mm x 1.55mm 1 sumida (4) 0.47h inductor, 94m ? 3.2mm x 3.2mm x 1.55mm r1 crcw04021002f vishay-dale (3) 100k ? 1% 0402 resistor 1 crcw04026652f vishay-dale (3) 66.5k ? 1% 0402 resistor for 2.5v out crcw04021243f vishay-dale (3) 124k ? 1% 0402 resistor for 1.8v out crcw04022003f vishay-dale (3) 200k ? 1% 0402 resistor for 1.5v out crcw04024023f vishay-dale (3) 402k ? 1% 0402 resistor for 1.2v out r2 open for 1.0v out 1 r3 crcw040220r5f vishay (3) 20 ? 1% 0402 resistor 1 u1 MIC2285Aymt micrel (5) 8mhz synchronous buck regulator with lowq ? mode 1 notes : 1. avx: www.avxcorp.com 2. murata: www.murata.com 3. vishay: www.vishay.com 4. sumida: www.sumida.com 5. micrel, inc.: www.micrel.com
micrel, inc. MIC2285A august 2007 14 m9999-083107-b package information 10-pin 2mm x 2mm thin mlf ? (mt) 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 belie ved to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and specificati ons at any time without notification to the customer. micrel products are not designed or authori zed for use as components in life support app liances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. li fe support devices or systems are devices or systems that (a ) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to r esult in a significant injury to the user. a purchaser ?s use or sale of micrel products for us e in life support appliances, devices or sys tems is a purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2007 micrel, incorporated.

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