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general description the max8884y/max8884z step-down converters withdual low-dropout (ldo) linear regulators are intended to power low-voltage microprocessors, dsps, camera and wi-fi modules, or other point of load applications in portable devices. these ics feature high efficiency with small external component size. the step-down converter output voltage is pin selectable between 1.2v and 1.8v, and provides guaranteed output current of 700ma. the 2/4mhz hysteretic-pwm control scheme allows for tiny external components and reduces no-load operating current to 50a. two low quiescent current, low-noise ldos operate down to 2.7v supply voltage. two switch- ing frequency options are availablemax8884y (2mhz) and max8884z (4mhz)allowing optimization for small- est solution size or highest efficiency. fast switching allows the use of small ceramic 2.2f input and output capacitors while maintaining low ripple voltage. the max8884y/max8884z have individual enables for each output, maximizing flexibility. the max8884y/max8884z are available in a 16-bump, 2mm x 2mm csp package (0.7mm max height). applications cell phones/smartphonespda and palmtop computers portable mp3 and dvd players digital cameras, camcorders pcmcia cards handheld instruments features ? step-down converterpin-selectable output voltage (1.2v/1.8v) 2mhz or 4mhz switching frequency low-output voltage ripple 700ma output drive capability simple logic on/off control tiny external components ? low-noise ldos2 x 300ma ldo pin-selectable output voltage (ldo1) low 26 v rms (typ) output noise high 65db (typ) psrrsimple logic on/off control ? low 0.1 a shutdown current ? 2.7v to 5.5v supply voltage range ? thermal shutdown ? tiny, 2mm x 2mm x 0.65mm csp package (4x4 grid) max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp ________________________________________________________________ maxim integrated products 1 19-4418; rev 1; 1/10 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available typical application circuit appears at end of data sheet. agnd pgnd refbp nc1 buck_en lx ldo2 ldo2_en max8884y max8884z sel in1a in2 in1b ldo1_en fb ldo1 nc2 top view(bumps on bottom) a1 a2 a3 a4 b1 b2 b3 b4 c1 c2 c3 c4 d1 d2 d3 d4 csp pin configuration in1a lx fb 2.2 h agnd buck_en ldo1_en ldo2_en in2 batt 2.7v to 5.5v batt 2.7v to 5.5v buck on/off buck 1.2v/1.8v refbp in1b ldo1 on/off ldo2 on/off ldo2 ldo1 v ldo2 up to 300ma v ldo1 up to 300ma pgnd sel 2.2 f 2.2 f buck/ldo1 voltage selection max8884y max8884z typical operating circuit ordering information part pin-package switching frequency max8884y ereke+t 16 csp 2mhz max8884z ereke+t 16 csp 4mhz note: all devices are specified over the -40c to +85c operat- ing temperature range. + denotes a lead(pb)-free/rohs-compliant package. t = tape and reel. downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp 2 _______________________________________________________________________________________ absolute maximum ratingselectrical characteristics (v in1a = v in1b = v in2 = v ldo1_en = v ldo2_en = v buck_en = 3.6v. t a = -40c to +85c, typical values are at t a = +25c, unless otherwise noted.) (note 1) stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. in1a, in1b, in2, refbp to agnd ........................-0.3v to +6.0v fb to pgnd ...........................................................-0.3v to +6.0v sel, buck_en to agnd...............-0.3v to (v in1a /v in1b + 0.3v) ldo1, ldo2, ldo1_en, ldo2_en to agnd.................................................-0.3v to (v in2 + 0.3v) in2 to in1a, in1b ..................................................-0.3v to +0.3v agnd to pgnd .....................................................-0.3v to +0.3v in1a, in1b, lx current .....................................................1a rms continuous power dissipation (t a = +70c) 16-bump csp (derate 12.5mw/c above +70c) ..............1w operating temperature .......................................-40c to +85c junction temperature ......................................................+150c storage temperature range .............................-65c to +150c bump temperature*.........................................................+260c parameter conditions min typ max units input supply input voltage v in1a , v in1b , v in2 2.7 5.5 v input undervoltage threshold v in1a , v in1b , v in2 rising, 180mv typical hysteresis 2.52 2.63 2.70 v t a = +25c 0.1 4 shutdown supply current v buck_en = v ldo1_en = v ldo2_en = 0 t a = +85c 0.1 a v buck_en = 0, i ldo1 = i ldo2 = 0a 140 230 a no-load supply current v ldo1_en = v ldo2_en = 0, i buck = 0a, no switching 50 80 a thermal protection thermal shutdown t a rising, 20c typical hysteresis +160 c logic control logic input-high voltage (buck_en, sel, ldo1_en, ldo2_en) 2.7v v in1a = v in1b = v in2 5.5v 1.3 v logic input-low voltage (buck_en, sel, ldo1_en, ldo2_en) 2.7v v in1a = v in1b = v in2 5.5v 0.4 v t a = +25c 0.01 1 logic input current (buck_en, sel, ldo1_en, ldo2_en) v il = 0 or v ih = v in1a = 5.5v t a = +85c 0.1 a fb sel = agnd, i buck = 0a 1.18 1.22 1.24 v buck converter output voltage v sel = v in1a , i buck = 0a 1.78 1.80 1.85 v t a = +25c 0.01 1 fb leakage current v in1a = v in1b = v in2 = 5.5v, v fb = 0 t a = +85c 1 a lx p-channel mosfet switch, i lx = -40ma 0.18 0.30 on-resistance n-channel mosfet rectifier, i lx = 40ma 0.15 0.25 * these ics are constructed using a unique set of packaging techniques imposing a limit on the thermal profile used during board level solder attach and rework. this limit permits only the use of the solder profiles recommended in the industry-standard specification, jedec 020a, paragraph 7.6, table 3 for ir/vpr and convection reflow. preheating is required. hand or wave soldering is not allowed. downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp _______________________________________________________________________________________ 3 parameter conditions min typ max units t a = +25c 0.1 1 lx leakage current v in1a = v in1b = v in2 = 5.5v, v lx = 0 t a = +85c 1 a p-channel mosfet peak current limit v lx = 0 0.8 1.0 1.2 a n-channel mosfet valley current limit 0.6 0.8 1.0 a max8884y_ 40 n-channel mosfet zero-crossing threshold max8884z_ 60 ma minimum on-time 0.07 s minimum off-time 0.06 s power-up delay from v buck_en rising to v lx rising 120 250 s ldo1, ldo2 sel = agnd 1.764 1.800 1.836 output voltage v ldo1 v in2 = 5.5v, i ldo_ = 1ma; v in2 = 3.4v, i ldo_ = 100ma sel = in1_ 2.800 v output voltage v ldo2 v in2 = 5.5v, i ldo_ = 1ma; v in2 = 3.4v, i ldo_ = 100ma 2.770 2.800 2.830 v output current 300 ma current limit v ldo_ = 0 310 450 750 ma dropout voltage i ldo_ = 100ma, t a = +25c (v ldo_ 2.5v) 70 200 mv line regulation v in2 stepped from 3.5v to 5.5v, i ldo_ = 100ma 2.4 mv load regulation i ldo_ stepped from 50a to 200ma 25 mv power-supply rejection v ldo_ / v in2 10hz to 100khz, v ldo_ = 1.8v, c ldo_ = 2.2f, i ldo_ = 30ma 65 db output noise 10hz to 100khz, v ldo_ = 1.8v, c ldo_ = 2.2f, i ldo_ = 30ma 26 v rms 0 < i ldo_ < 10ma 0.1 10ma < i ldo_ < 200ma 1 output capacitor for stable operation 200ma < i ldo_ < 300ma 2.2 f shutdown output impedance v ldo1_en = v ldo2_en = 0 100 power-up delay from v ldo_en rising to v ldo_ output rising 150 250 s refbp refbp output voltage 0 i refbp 1a 1.237 1.250 1.263 v refbp supply rejection v in2 stepped from 2.55v to 5.5v 0.2 5 mv electrical characteristics (continued)(v in1a = v in1b = v in2 = v ldo1_en = v ldo2_en = v buck_en = 3.6v. t a = -40c to +85c, typical values are at t a = +25c, unless otherwise noted.) (note 1) note 1: all devices are 100% production tested at t a = +25c. limits over the operating temperature range are guaranteed by design. downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp 4 _______________________________________________________________________________________ step-down converter efficiency vs. load current, v out = 1.8v max8884y/z toc01 load current (ma) efficiency (%) 100 10 40 50 60 70 80 90 100 30 1 1000 max8884y, v in = 3.2v = 3.6v= 4.2v max8884z, v in = 3.2v = 3.6v= 4.2v step-down converter efficiency vs. load current, v out = 1.2v max8884y/z toc02 load current (ma) efficiency (%) 100 10 40 50 60 70 80 90 100 30 11 0 0 0 max8884y, v in = 3.2v = 3.6v= 4.2v max8884z, v in = 3.2v = 3.6v= 4.2v step-down converter no-load supply current vs. input voltage max8884y/z toc03 input voltage (v) supply current ( a) 5 4 3 2 1 50 100 150 200 250 300 0 06 v buck_en = v in v ldo1_en = v ldo2_en = 0 v in falling v in rising max8884y max8884z step-down output voltage vs. load current (voltage positioning) max8884y/z toc04 load current (ma) output voltage (v) 100 10 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.91.0 1 1000 sel = in1_ sel = agnd max8884z step-down converter light load switching waveforms max8884y/z toc05 400ns/div i lx v out v lx 0a2v/div 100ma/div ac-coupled20mv/div 0v max8884y step-down converter light load switching waveforms max8884y/z toc06 1 s/div i lx v out v lx 0a2v/div 100ma/div ac-coupled10mv/div 0v i load = 50ma max8884z step-down converter heavy load switching waveforms max8884y/z toc07 200ns/div i lx v out v lx 0a2v/div 500ma/div ac-coupled10mv/div 0v i load = 500ma max8884y step-down converter heavy load switching waveforms max8884y/z toc08 400ns/div i lx v out v lx 0a2v/div 500ma/div ac-coupled10mv/div 0v i load = 500ma typical operating characteristics (v in = v in1a = v in1b = v in2 = 3.6v, v buck = 1.2v, v ldo1 = 1.8v, v ldo2 = 2.8v, max8884yevkit, t a = +25c, unless otherwise noted.) downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp _______________________________________________________________________________________ 5 max8884z step-down converter line transient response max8884y/z toc12 10 s/div i lx v in v out 0a 1v/div200ma/div ac-coupled20mv/div i load = 500ma 4v 4v 3.5v max8884y step-down converter load transient max8884y/z toc14 20 s/div i lx v out i out 0a 1.8v dc offset100mv/div 500ma/div 500ma/div0a 500ma 10ma 10ma _______________________________________________________________________________________ 5 typical operating characteristics (continued) (v in = v in1a = v in1b = v in2 = 3.6v, v buck = 1.2v, v ldo1 = 1.8v, v ldo2 = 2.8v, max8884yevkit, t a = +25c, unless otherwise noted.) max8884y step-down converter line transient response max8884y/z toc11 10 s/div i lx v in v out 0a 1v/div200ma/div ac-coupled20mv/div i load = 500ma 3.5v 4v 4v max8884z step-down converter load transient max8884y/z toc13 20 s/div v out i lx i out 0a 500ma/div 0a 500ma/div 1.8v dc offset100mv/div 10ma 10ma 500ma max8884y step-down converter soft-start waveforms max8884y/z toc10 40 s/div i lx i in1 v out v buck_en 0a2v/div 500ma/div 0a 200ma/div 0v 1v/div0v i load = 500ma max8884z step-down converter soft-start waveforms max8884y/z toc09 40 s/div i in1 v out i lx v buck_en 0a2v/div 500ma/div 0a 200ma/div 0v 1v/div0v i load = 500ma downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp 6 _______________________________________________________________________________________ typical operating characteristics (continued) (v in = v in1a = v in1b = v in2 = 3.6v, v buck = 1.2v, v ldo1 = 1.8v, v ldo2 = 2.8v, max8884yevkit, t a = +25c, unless otherwise noted.) ldo power supply ripple rejection, v out = 1.8v max8884y/z toc18 frequency (khz) ripple rejection (db) 100 10 0.1 1 10 20 30 40 50 60 70 80 0 0.01 1000 i ldo = 30ma ldo output voltage noise waveform, v out_ = 1.8v max8884y/z toc20 400 s/div max8884y/max8884z ldo1 = 1.8 at 30ma v in = 3.6v 50 v/div v n = 26.1 v rms , f = 100hz to 100khz, i ldo_ = 30ma ldo2 dropout voltage vs. load current max8884y/z toc17 load current (ma) dropout voltage (v) 250 200 150 100 50 50 100 150 200 250 0 03 0 0 ldo power supply ripple rejection, v out = 2.8v max8884y/z toc19 frequency (khz) ripple rejection (db) 100 10 1 0.1 10 20 30 40 50 60 70 0 0.01 1000 i ldo_ = 30ma ldo1, ldo2 input supply current vs. input voltage max8884y/z toc16 input voltage (v) supply current ( a) 5 4 3 2 1 50 100 150 200 250 300 350 0 06 v ldo1_en = v ldo2_en = v in , v buck_en = 0 max8884y step-down converter shutdown waveforms max8884y/z toc15 10 s/div i lx v out v buck_en 0v 1v/div0v 5v/div 500ma/div0a i load = 500ma downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp _______________________________________________________________________________________ 7 _______________________________________________________________________________________ 7 typical operating characteristics (continued) (v in = v in1a = v in1b = v in2 = 3.6v, v buck = 1.2v, v ldo1 = 1.8v, v ldo2 = 2.8v, max8884yevkit, t a = +25c, unless otherwise noted.) ldo1, ldo2 load transient response max8884y/z toc24 20 s/div i ldo1 v ldo2 i ldo2 v ldo1 ac-coupled10mv/div ac-coupled10mv/div 50ma/div 50ma/div 1ma 1ma 1ma 1ma 40ma 40ma ldo1, ldo2 line transient max8884y/z toc23 10 s/div v ldo1 v in v ldo2 ac-coupled5mv/div ac-coupled5mv/div 1v/div i ldo1 = i ldo2 = 100ma 4v 4v 3.5v ldo output-noise spectral density vs. frequency, v ldo_ = 2.8v max884y/z toc22 frequency (khz) 100 10 1 0.1 100 1000 10,000 10 0.01 1000 i ldo_ = 30ma noise density (nv (hz)) ldo output-noise spectral density vs. frequency, v ldo_ = 1.8v max884y/z toc21 frequency (khz) noise density (nv (hz)) 100 10 1 0.1 100 1000 10,000 10 0.01 1000 i ldo_ = 30ma ldo1, ldo2 startup and shutdown response max8884y/z toc26 400 s/div v ldo1 v ldo1_en = v ldo2_en v ldo2 2v/div0v 2v/div0v 2v/div0v ldo1, ldo2 load transient response near dropout max8884y/z toc25 20 s/div i ldo1 v ldo2 i ldo2 v ldo1 ac-coupled10mv/div ac-coupled10mv/div 50ma/div50ma/div 1ma 1ma 40ma 1ma 1ma 40ma v in2 = v ldo2 + 200mv downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp 8 _______________________________________________________________________________________ refbp soft-start c refbp = 0.15 f max8884y/z toc28 100 s/div v ldo1_en v refbp v ldo1 1v/div0v 2v/div0v 1v/div0v refbp soft-start c refbp = 0.033 f max8884y/z toc27 100 s/div v ldo1_en v refbp v ldo1 1v/div0v 2v/div0v 0v 1v/div max8884y switching frequency vs. output current (v out = 1.2v) max8884y/z toc30 load current (ma) switching frequency (mhz) 700 500 300 1.2 1.4 1.6 1.8 2.0 2.2 2.41.0 100 900 v in = 4.2v v in = 3.6v v in = 3v c in = c out = 2.2 f, l = 2.2 h max8884y switching frequency vs. output current (v out = 1.8v) max8884y/z toc29 load current (ma) switching frequency (mhz) 700 500 300 1.2 1.4 1.6 1.8 2.0 2.2 2.41.0 100 900 v in = 4.2v v in = 3.6v v in = 3v c in = c out = 2.2 f, l = 2.2 h max8884z switching frequency vs. output current (v out = 1.2v) max8884y/z toc32 load current (ma) switching frequency (mhz) 700 500 300 3.0 4.0 4.5 3.5 5.02.5 100 900 c in = c out = 2.2 f, l = 2.2 h v in = 3.6v v in = 3v v in = 4.2v max8884z switching frequency vs. output current (v out = 1.8v) max8884y/z toc31 load current (ma) switching frequency (mhz) 700 500 300 2.5 3.0 3.5 4.0 4.5 5.02.0 100 900 v in = 4.2v v in = 3.6v v in = 3v c in = c out = 2.2 f, l = 2.2 h typical operating characteristics (continued) (v in = v in1a = v in1b = v in2 = 3.6v, v buck = 1.2v, v ldo1 = 1.8v, v ldo2 = 2.8v, max8884yevkit, t a = +25c, unless otherwise noted.) downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp _______________________________________________________________________________________ 9 detailed description the max8884y/max8884z are designed to power thesubcircuits within a system. these ics contain a high- frequency, high-efficiency step-down converter and two ldos. the step-down converter delivers 700ma with either 1.2v or 1.8v selectable output voltage using sel. the hysteretic pwm control scheme provides extremely fast transient response, while 2mhz and 4mhz switch- ing frequency options allow the trade-off between effi- ciency and the smallest external components. the max8884y/max8884z linear regulators can be used to power loads requiring a low output noise supply. step-down converter control scheme a hysteretic pwm control scheme ensures high efficien-cy, fast switching, fast transient response, low-output voltage ripple, and physically tiny external components. the control scheme is simple: when the output voltage is below the regulation threshold, the error comparator begins a switching cycle by turning on the high-side switch. this high-side switch remains on until the mini- mum on-time expires and output voltage is within regu- lation, or the inductor current is above the current-limit threshold. once off, the high-side switch remains off until the minimum off-time expires and the output volt- age falls again below the regulation threshold. during pin description pin name function a1 refbp reference noise bypass. bypass refbp to agnd with a 0.033f ceramic capacitor to reduce noiseon the ldo outputs. refbp is internally pulled to ground through a 1k resistor during shutdown. a2 agnd low-noise analog ground. connect to common ground plane. a3 nc1 no internal connection. connect nc1 to ground. a4 pgnd power ground for step-down converter. connect to common ground plane. b1 ldo2 300ma ldo regulator 2 output. for 300ma application, bypass ldo2 with a 2.2f ceramic capacitoras close as possible to ldo2 and agnd. for low-output current capability, up to 10ma, an output capacitor of 0.1f is sufficient to keep the output voltage stable. ldo2 is internally pulled to ground through a 100 resistor when this regulator is disabled. b2 buck_en step-down converter enable input. connect buck_en to in1_ or logic-high for normal operation.connect buck_en to agnd or logic-low for step-down shutdown mode. b3 ldo2_en ldo2 enable input. connect ldo2_en to in2 or logic-high for normal operation. connect ldo2_en toagnd or logic-low for ldo2 shutdown mode. b4 lx inductor connection. connect an inductor from lx to the output of the step-down converter. c1 in2 supply voltage input for ldo1, ldo2, and internal reference. connect in2 to a battery or supplyvoltage from 2.7v to 5.5v. bypass in2 with a 4.7f ceramic capacitor as close as possible to in2 and agnd. connect in2 to the same source as in1a and in1b. c2 sel output voltage selection for ldo1 and step-down converter. connect to in1_ or agnd for output voltage selection. see table 1. c3, c4 in1b, in1a supply voltage input for step-down converter. connect in1b and in1a to a battery or supply voltagefrom 2.7v to 5.5v. bypass the connection of in1b and in1a with a 2.2f ceramic capacitor as close as possible to in1b, in1a, and pgnd. in1a and in1b are internally connected together. connect in1a and in1b to the same source as in2. d1 ldo1 300ma ldo regulator 1 output. for 300ma application, bypass ldo1 with a 2.2f ceramic capacitoras close as possible to ldo1 and agnd. for low-output current capability, up to 10ma, an output capacitor of 0.1f is sufficient to keep output voltage stable. ldo1 is internally pulled to agnd through a 100 resistor when this regulator is disabled. d2 ldo1_en ldo1 enable input. connect ldo1_en to in2 or logic-high for normal operation. connect ldo1_en toagnd or logic-low for ldo1 shutdown mode. d3 nc2 no internal connection. connect nc2 to ground. d4 fb fb is connected to the internal feedback network downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp 10 ______________________________________________________________________________________ the off period, the low-side synchronous rectifier turnson and remains on until the high-side switch turns on again. the internal synchronous rectifier eliminates the need for an external schottky diode. hysteretic control is sometimes referred to as ripple con- trol, since voltage ripple is used to control when the high- side and low-side switches are turned on and off. to ensure stability with low esr ceramic output capacitors, the max8884y/max8884z combine ripple from the out- put with the ramp signal generated by the switching node (lx). this is seen in figure 2 with resistor r1 and capacitor c1 providing the combined ripple signal. injecting ramp from the switch node also improves line regulation, since the slope of the ramp adjusts with changes in input voltage. hysteretic control has a significant advantage over fixed frequency control schemes: fast transient response. hysteretic control uses an error comparator, instead of an error amplifier with compensation, and there is no fixed frequency clock. therefore, a hysteretic converter reacts virtually immediately to any load transient on the output, without having to wait for a new clock pulse, or for the output of the error amplifier to move, as with a fixed-frequency converter. with a fixed-frequency step-down converter, the magni- tude of output voltage ripple is a function of the switching frequency, inductor value, output capacitor and esr, and input and output voltage. since the inductance value and switching frequency are fixed, the output ripple varies with changes in line voltage. with a hysteretic step-down converter, since the ripple voltage is essen- tially fixed, the switching frequency varies with changes in line voltage. some variation with load current is also seen, however, this is part of what gives the hysteretic converter its great transient response. see the typical operating characteristics section for more information on how switching frequency canchange with load and line changes. at inductor currents below 40ma (60ma), the max8884y (max8884z) automatically switches to pulse-skipping mode to improve light-load efficiency. output voltage ripple remains low at all loads, while the skip-mode switching frequency remains ultrasonic down to 1ma (typ) loads. voltage positioning load regulation the max8884y/max8884z step-down converters utilizea unique feedback network. by taking a dc feedback from the lx node through r1 in the block diagram , the usual phase lag due to the output capacitor is removed, making the loop exceedingly stable andallowing the use of very small ceramic output capaci- tors. to improve the load regulation, resistor r3 is included in the feedback (see the block diagram ). this configuration yields load regulation equal to half theinductors series resistance multiplied by the load cur- rent. this voltage positioning load regulation greatly reduces overshoot during load transients. sel output voltage selection sel is used to determine the output voltage of the buckconverter and ldo1. see table 1. shutdown mode drive buck_en to logic-low to place the max8884y/max8884z step-down converter in shutdown mode. in shutdown, the control circuitry, internal switching mosfet, and synchronous rectifier turn off and lx becomes high impedance. the ldos are individually enabled. connect ldo1_en and ldo2_en to gnd or logic-low to place ldo1 and ldo2 in shutdown mode. in shutdown, the outputs of the ldos are pulled to ground through an internal 100 ? resistor. when the step-down converter and all ldos are in shut-down, the max8884y/max8884z enter a very low-power state, where the input current drops to 0.1a (typ). step-down converter soft-start the max8884y/max8884z step-down converter usesinternal soft-start circuitry to limit inrush current at startup, reducing transients on the input source. soft-start is partic- ularly useful for supplies with high output impedance such as li+ and alkaline cells. see the soft-start waveforms in the typical operating characteristics . vv ir i load cu buck buck no load load dcr load = = __ 2 r rrent r dc impedance of inductor v dcr buck no lo = __a ad v or v depending on sel = 12 18 .. sel buck converter output voltage (v) ldo1 output voltage (v) agnd 1.2 1.8 in1_ 1.8 2.8 table 1. sel output voltage selection downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp ______________________________________________________________________________________ 11 thermal shutdown thermal shutdown limits total power dissipation in themax8884y/max8884z. if the junction temperature exceeds +160c, thermal shutdown circuitry turns off the max8884y/max8884z, allowing the ics to cool. the ics turn on and begin soft-start after the junction temperature cools by 20c. this results in a pulsed out- put during continuous thermal-overload conditions. applications information output voltages the max8884y/max8884z dc-dc step-down convert-er sets the buck and ldo1 output voltage based on the state of sel. see table 1. contact the factory for other output voltage options. ldo dropout voltage the regulators minimum input/output differential (ordropout voltage) determines the lowest usable supply voltage. in battery-powered systems, this determines the useful end-of-life battery voltage. because the max8884y/max8884z ldos use a p-channel mosfet pass transistor, their dropout voltages are a function of drain-to-source on-resistance (r ds(on) ) multiplied by the load current (see the typical operating characteristics ). inductor selection the max8884y operates with a switching frequency of2mhz and utilizes a 2.2h inductor. the max8884z operates with a switching frequency of 4mhz and uti- lizes a 1h inductor. the higher switching frequency of the max8884z allows the use of physically smaller inductors at the cost of lower efficiency. the lower switching frequency of the max8884y results in greater efficiency at the cost of a physically larger inductor. see the typical operating characteristics for efficiency graphs for both the max8884y and the max8884z.the inductors dc current rating only needs to match the maximum load of the application because the max8884y/max8884z feature zero current overshoot during startup and load transients. for optimum transient response and high efficiency, choose an inductor with dc series resistance in the 50m ? to 150m ? range. see table 2 for suggested inductors and manufacturers. output capacitor selection for the dc-dc step-down converter, the output capacitorc buck is required to keep the output voltage ripple small and ensure regulation loop stability. c buck must have low impedance at the switching frequency. ceramic capaci- tors with x5r or x7r dielectric are highly recommendeddue to their small size, low esr, and small temperature coefficients. due to the unique feedback network, the out- put capacitance can be very low. a 2.2f ceramic capaci- tor is recommended for most applications. for optimum load-transient performance and very low output ripple, the output capacitor value can be increased. for ldo1 and ldo2, the minimum output capacitance required is dependent on the load currents. for loads lighter than 10ma, it is sufficient to use a 0.1f ceramic capacitor for stable operation over the full temperature range. for loads up to 200ma, an output capacitor of 1f is sufficient for stable operation over the entire tem- perature range. operating the ldo at maximum rated current the ldo1 and ldo2 requires a 2.2f ceramic capacitor. using larger output capacitors reduces out- put noise and improves load-transient response, stabili- ty, and power-supply rejection. note that some ceramic dielectrics exhibit large capaci- tance and esr variation with temperature. with dielectrics such as z5u and y5v, it is necessary to use 4.7f or more to ensure stability at temperatures below -10c. with x7r or x5r dielectrics, 2.2f is sufficient at all operating tem- peratures. these regulators are optimized for ceramic capacitors. tantalum capacitors are not recommended. input capacitor selection the input capacitor (c in1 ) of the dc-dc step-down converter reduces the current peaks drawn from thebattery or input power source and reduces switching noise in the max8884y/max8884z. the impedance of c in1 at the switching frequency should be kept very low. ceramic capacitors with x5r or x7r dielectric arehighly recommended due to their small size, low esr, and small temperature coefficients. a 2.2f ceramic capacitor is recommended for most applications. for optimum noise immunity and low input ripple, the input capacitor value can be increased. for the ldos, use an input capacitance equal to the value of the sum of the output capacitance of ldo1 and ldo2. larger input capacitor values and lower esr pro- vide better noise rejection and line transient response. note that some ceramic dielectrics exhibit large capaci- tance and esr variation with temperature. with dielectrics such as z5u and y5v, it may be necessary to use two times the sum of the output capacitor value of ldo1 and ldo2 (or larger) to ensure stability at temperatures below -10c. with x7r or x5r dielectrics, a capacitance equal to the sum is sufficient at all operating temperatures. downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp 12 ______________________________________________________________________________________ table 2. suggested inductors manufacturer series inductance (h) esr ( ) current rating (ma) dimensions (mm) cb2016t 1.0 2.2 0.09 0.13 510 2.0 x 1.6 x 1.8 = 5.8mm 3 taiyo yuden cb2518t 2.2 4.7 0.09 0.13 510 340 2.5 x 1.8 x 2.0 = 9mm 3 mipf2520 1.0 1.5 2.2 0.05 0.07 0.08 1500 1500 1300 2.5 x 2.0 x 1.0 = 5mm 3 fdk mipf2016 1.0 2.2 0.11 1100 2.0 x 1.6 x 1.0 = 3.2mm 3 murata lqh32c_53 1.0 2.2 0.06 0.10 1000 790 3.2 x 2.5 x 1.7 = 14mm 3 d3010fb 1.0 0.20 1170 3.0 x 3.0 x 1.0 = 9mm 3 d2812c 1.2 2.2 0.09 0.15 860 640 3.0 x 3.0 x 1.2 = 11mm 3 d310f 1.5 2.2 0.13 0.17 1230 1080 3.6 x 3.6 x 1.0 = 13mm 3 toko d312c 1.5 2.2 0.10 0.12 1290 1140 3.6 x 3.6 x 1.2 = 16mm 3 cdrh2d09 1.2 1.5 2.2 0.08 0.09 0.12 590 520 440 3.0 x 3.0 x 1.0 = 9mm 3 sumida cdrh2d11 1.5 2.2 3.3 0.05 0.08 0.10 680 580 450 3.2 x 3.2 x 1.2 = 12mm 3 coilcraft lpo3310 1.0 1.5 2.2 0.07 0.10 0.13 1600 1400 1100 3.3 x 3.3 x 1.0 = 11mm 3 elc3fn 1.0 2.2 0.08 0.12 1400 1000 3.2 x 3.2 x 1.2 = 12mm 3 panasonic ell3gm 1.0 2.2 0.07 0.10 1400 1100 3.2 x 3.2 x 1.5 = 15mm 3 hitachi ksli-252010 1.5 2.2 0.070 0.100 2200 1800 2.5 x 2.0 x 1.0 = 5mm 3 downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp ______________________________________________________________________________________ 13 reference noise bypass capacitor selection the refbp capacitor reduces the output noise of ldo1and ldo2. a value of 0.033f is sufficient for most appli- cations. this value can be increased up to 0.150f with some effect on the soft-start time of the ldos. see the typical operating characteristics for more information. do not use values greater than 0.150f as this degradesthe performance of the internal reference voltage and has a corresponding impact on all output voltages. ceramic capacitors with x5r or x7r dielectric are high- ly recommended due to their small size, low esr, and small temperature coefficients. note that some ceramic dielectrics exhibit large capacitance and esr variation with temperature. with dielectrics such as z5u and y5v, it may be necessary to use two times the recom- mended value to achieve desired output noise perfor- mance at temperatures below -10c. tantalum capacitors are not recommended. thermal considerations in most applications, the max8884y/max8884z do notdissipate much heat due to their high efficiency. but in applications where the max8884y/max8884z run at high ambient temperature with heavy loads, the heat dissipat- ed may exceed the maximum junction temperature of the part. if the junction temperature reaches approximately +160c, all power switches are turned off and lx and fb become high impedance, and ldo1 and ldo2 are pulled down to ground through an internal 100 ? resistor. the max8884y/max8884z maximum power dissipationdepends on the thermal resistance of the ic package and circuit board, the temperature difference between the die junction and ambient air, and the rate of airflow. the power dissipated in the device, p diss , is: where buck is the efficiency of the dc-dc step-down converter, and p buck is the output power of the dc-dc step-down converter.the maximum allowed power dissipation, p max , is: where (t jmax - t a ) is the temperature difference between the max8884y/max8884z die junction andthe surrounding air, and ja is the thermal resistance of the junction through the pcb, copper traces, and othermaterials to the surrounding air. pcb layout high switching frequencies and relatively large peakcurrents make the pcb layout a very important part of design. good design minimizes excessive emi on the feedback paths and voltage gradients in the ground plane, resulting in a stable and well regulated output. minimize the ground loop formed by c in1 , c buck , and pgnd. to do this, connect c in1 close to in1a/in1b and pgnd. connect the inductor and output capacitoras close as possible to the ic and keep their traces short, direct, and wide. keep noisy traces, such as the lx node, as short as possible. connect agnd and pgnd to the common ground plane. figure 1 illustrates an example pcb layout and routing scheme. p tt max j max a ja = () _ pp buck ivv i vv diss buck ldo in ldo ldo in ldo = ? ? ? ? ? ? ++ 1 1 12 1 2 2 2 ()( ) downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp 14 ______________________________________________________________________________________ b3 a1 a2 a3 a4 b1 b2 b4 c1 c2 c3 c4 d1 d3 d4 buck ldo1 4.0mm 3.8mm ldo2 in gnd sel d2 ldo2_en buck_en ldo1_en pgnd lx in1a fb nc2 in1b ldo1_en ldo1 in2 ldo2 buck_en sel ldo2_en nc1 agnd refbp c refbp c ldo2 c ldo1 c in2 c in1 l buck c buck figure 1. recommended pcb layout downloaded from: http:///
max8884y/max8884z pwm logic step-down current limit pwm error amp lxpgnd fb in1a r1r2 r6 r7 c2 c1 in2 r8r7 erroramp error amp current limit refbp ldo1 ldo1_en r11r10 current limit refbp ldo2 ldo2_en r9 r12 ref refbp agnd ref ldo1_enldo2_en sel in1b buck_en control logic sel sel max8884y max8884z r3 block diagram 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp ______________________________________________________________________________________ 15 downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp 16 ______________________________________________________________________________________ package type package code document no. 16 csp r162a2+1 21-0226 2?mhz buck fb ref ldo1 control lx 2.2 h (max8884y) 1.0 h (max8884z) pgnd in1a sel refbpagnd ldo1 ldo2 in2 gpiogpio gpio baseband processor camera module core digital analog 1.2v in1b ldo2_en ldo1_en buck_en 4.7 f li+ battery 2.2 f 2.2 f 2.2 f 2.2 f 0.033 f max8884y max8884z ldo2 typical application circuit package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to th e package regardless of rohs status. downloaded from: http:///
max8884y/max8884z 700ma dc-dc step-down converters with dual 300ma ldo in 2mm x 2mm csp maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 17 ? 2010 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 4/09 initial release 1 1/10 added switching frequency tocs and updated step-down converter control scheme section 8, 10 downloaded from: http:///

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