general description the MAX77231 is optimized for boost applications, requiring very low ripple/noise and small pcb space. output ripple and noise are suppressed to 35v rms (in 1mhz bw) by a pmos linear post-regulator set 0.5v below the boost regulator output to reject noise while optimizing efficiency. the boost regulator operates using a 1h/400ma inductor and 2.2f (0.22 (min) after derating) output capacitance. fast transient response and stable operation are guaranteed using a current-limited pfm architecture. a pmos low-noise linear post-regulator attenuates boost converter ripple by ~50db (10mhz bw) before delivering 11.2v to the load. other output voltages up to 16.2v can be factory set. the ldo also disconnects the load from the boost during shutdown, allowing the output to fall to 0v (true shutdown). active discharge can also be activated. the MAX77231 is packaged in a 9-bump wafer-level package (wlp), providing a compact layout when combined with the inductor and external capacitors. total solution size is less than 7mm 2 . benefts and features ultra-small solution size (< 7mm 2 ) 35v rms (typ) output ripple/noise 11.2v/10ma output output factory trimmable from 11.2v to 16.2v 125a no load supply current output on < 1a shutdown supply current true shutdown load disconnect selectable active discharge 9-bump, 1.238mm x 1.238mm x 0.35mm wlp applications low-noise bias supply sensor bias supply ordering information appears at end of data sheet. 19-6658; rev 2; 5/16 typical operating circuit enm input 2.7 to 4.8v lx bstp out gnd bst in pgnd on off l1 1h 400ma c1 2.2uf 6.3v c2 2.2f 25v c3 2.2f 25v output 11.2v 10ma MAX77231 ens MAX77231 2.75v to 4.8v input, 10ma output, 35 v rms ultra-low noise boost regulator evaluation kit available
bst, bstp, out to gnd ...................................... -0.3v to +22v bst to bstp ........................................................ -0.3v to +0.3v bst to out ............................................................. -0.3v to +6v in, enm, ens to gnd ............................................ -0.3v to +6v pgnd to gnd ...................................................... -0.3v to +0.3v rms lx_ current (per bump) ................................................. 1a continuous power dissipation (t a = +70c) wlp (derate 6.7mw/c above +70c) ........................ 533mw operating temperature range ........................... -40c to +85c junction temperature ...................................................... +150c storage temperature range ............................ -65c to +150c bump temperature (soldering, reflow) ............................ +300c (v in = v enm = v ens = 3.7v, v bstp = v bst = 11.7v, v out = 11.2v, c in = c bst = c out = 2.2f, t a = -40c to +85c, figure 1, unless otherwise noted. typical values are at t a = +25c.) (note 2) electrical characteristics maxim integrated 2 note 1: package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four-layer board. for detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial . absolute maximum ratings parameter conditions min typ max units in operating range 2.75 4.8 v in undervoltage threshold when output is enabled/ disabled in rising 2.65 2.75 v in falling 2.4 2.55 shutdown supply current total of i in and i lx , v in = v lx = 4.8v, v out = v enm = v ens = 0v t a = +25c 0.01 1 a t a = +85c 0.1 a supply current output regulating, no load 120 a in supply current bst supply current not included 50 100 a bst supply current i bst + i bstp , v bst = 11.7v (not switching) 20 60 a boost regulator bst regulation voltage ldo output voltage is 0.5v less than bst -3% 11.7 +3% v bst output range factory trimmed 11.7 16.7 v lx maximum on-time 570 ns lx minimum off-time vin = 2.7v to 4.8v v bst = 11v 35 ns v bst = v in + 3.5v 35 ns v bst = v in 320 ns lx peak current limit static measurement (note 2) ma v in = 3.7v, t a = +25c 213 225 237 v in = 2.7v to 4.8v, over temperature 170 300 dynamic measurement (note 2) 350 lx inductor value 20% tolerance 1.0 to 4.7 h lx on resistance i lx = 150ma 250 600 m? lx shutdown leakage v lx = 18v t a =+25 c 0.05 5 a t a =+85 c 0.5 a diode forward voltage v lx to v bstp , v lx = 3.7v, i lx = 150ma 0.4 v boost effciency 0402 1h inductor v in = 3.7v, v bst = 11.7v, 3ma 76 % MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator www.maximintegrated.com
(v in = v enm = v ens = 3.7v, v bstp = v bst = 11.7v, v out = 11.2v, c in = c bst = c out = 2.2f, t a = -40c to +85c, figure 1, unless otherwise noted. typical values are at t a = +25c.) (note 2) note 2: limits are 100% production tested at t a = +25c. limits over the operating temperature range are guaranteed through cor - relation using statistical quality control (sqc) methods. static lx current limits test. note 3: in-circuit limit with 1h inductor is approximately 125ma higher than listed values due to current comparator delay. dynamic (in circuit) peak limit is typically 350ma. maxim integrated 3 electrical characteristics (continued) parameter conditions min typ max units linear regulator out regulation voltage i out = 0ma to 6ma -4% 11.2 +4% v out output range factory-trimmed output range (contact factory) 11.2 16.2 v output discharge current v enm = 0v, v ens = v bst = 3.7v, v out = 1v 15 ma psrr bst to out, f = 1mhz, i out = 5ma 50 db out output capacitance 20% tolerance, -90% voltage coeffcient 2.2 f logic (enm and ens) input threshold when output is enabled/ disabled rising 0.95 1.26 v falling 0.54 0.85 v ens pulldown resistance v ens = 1v, v enm = 0v 500 k? enm input leakage v enm = 0v to 4.8v, v ens = 0v t a = +25c 0.001 1 a t a = +85c 0.01 a transient/noise total output noise and ripple circuit of figure 1, i load = 0ma to 6ma, f = 100hz to 10mhz (-3db corners, frst order roll off) 35 v rms transient load regulation circuit of figure 1, i out = 0 to 6ma 20 mv p-p transient line regulation circuit of figure 2, at 16v load, v in = 2.7v to 4.8v, v in = 500mv step, t r = t f = 100mv/s 5 mv p-p startup time circuit of figure 2, at 16v load, from v enm and v ens high to v out = 16v 2 ms output active discharge time circuit of figure 2, at 16v load, from v enm low to v out < 0.1v 5 ms short-circuit output current v out = 0v 40 ma MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator www.maximintegrated.com
(t a = +25c, unless otherwise noted.) maxim integrated 4 typical operating characteristics 11.190 11.195 11.200 11.205 11.210 11.215 11.220 -40 -20 0 20 40 60 80 100 output voltage (v) temperature (oc) output voltage vs. temperature toc04 250 270 290 310 330 350 370 390 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 peak current ( ma ) input voltage (v) peak lx current vs. input voltage toc05 10mv/div 200ma/div 5v/div toc6 1s/div v out (ac) i l v lx typical operating waveforms 40 45 50 55 60 65 70 75 80 85 90 0.03 0.3 3 30 efficiency (%) load current (ma) out efficiency vs. load current toc01 bst 80 90 100 110 120 130 140 150 160 2.5 3.0 3.5 4.0 4.5 5.0 input current ( a ) input voltage (v) no - load input current vs. input voltage toc02 11.00 11.05 11.10 11.15 11.20 11.25 11.30 0 5 10 15 20 25 output voltage (v) load current (ma) output voltage vs. load current v in = 2.7v toc03 v in = 3.7v MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator www.maximintegrated.com
(t a = +25c, unless otherwise noted.) maxim integrated 5 typical operating characteristics (continued) 20mv/div 10ma/div toc10 100s/div v out i load load transient response (0ma - 6ma - 0ma) 2v/div load gate 0.1mv/div 50mv/div toc7 4s/div v out (1mhz bw) v bst output ripple and noise 5v/div 200ma/div toc8 200s/div v out i lx startup response (no load) 5v/div v enm 5v/div 200ma/div toc9 200s/div v out i lx startup response (6ma load) 5v/div v enm 5v/div 200ma/div toc11 4s/div v bst i lx short - circuit response 5v/div v out 0v MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator www.maximintegrated.com
maxim integrated 6 bump confguration bump description pgnd in ens lx enm gnd bstp bst out 1 2 3 a b c (view from top of package, pins down) name location function pgnd a1 power ground. connect to ground through a low-inductance trace. low side of internal lx switch. in a2 input supply voltage. connect this pin to the 2.5v to 4.8v input power source. connect a 2.2f/6.3v ceramic capacitor from in to ground. ens a3 slave enable input. logic-high enables the output. logic-low turns it off. typically, a 0.9v logic threshold with 50mv hysteresis. lx b1 inductor pin. connect a 1.0h inductor from this pin to the input voltage source. enm b2 master enable input. a logic-high on both enm and ens enables the output. logic-low turns the output off, while also enabling a 15ma (min) output discharge current. typically, a 0.9v logic threshold with 50mv hysteresis. agnd b3 analog ground bstp c1 boost power output. output of internal schottky diode. delivers up to 400ma current pulses at high switching speeds. bypass to ground through a low-inductance trace with a 2.2f/25v ceramic capacitor at bst/bstp. bstp should be connected to the linear regulator input at bst. bst c2 linear regulator input. connect this pin to the boost output, bstp, to supply the linear regulator when the part is enabled. connect a 2.2f/25v ceramic capacitor from bst/bstp to agnd to ensure proper operation. out c3 linear regulator low-noise/ripple output (when max77321 is enabled). out falls to 0v when disabled. connect a 2.2f/25v ceramic capacitor from out to ground. MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator www.maximintegrated.com
detailed description the MAX77231 is a low-noise boost regulator designed to occupy minimal pcb board space. a high-frequency pfm boost regulator creates an 11.7v supply, which is then post-regulated to 11.2v with a low-noise, high psrr pmos linear regulator (see figure 1 ). other output volt - ages up to 16.2v are available on request. boost converter an 11.7v (or other factory trimmed) output is generated by a current-limited, maximum on-time, minimum off- time, pfm boost converter. when the output drops below 11.7v, an internal nmos switch forces the input voltage across the inductor. the switch turns off when the inductor current reaches 350ma, and the lx pin is driven high by the inductor until the internal schottky diode, d1, turns on. inductor current is delivered to the boost output through the diode until the reverse inductor voltage causes the current to drop to 0ma, and the lx voltage drops. a maximum on-time timer prevents the lx switch from staying on longer than 570ns if resistive, or other, losses prevent the inductor current from reaching 350ma. if the inductor discharge time exceeds the 35ns minimum off time, and the bst output is still less than 11.7v, lx switches back down to 0v, and the current builds back up to 350ma. under this condition, the inductor current ramps back up before reaching 0ma, causing the boost to operate in continuous conduction mode. this mode is typically reached only during startup, when the bst output is much less than 11.7v. the typical switching frequency is: f sw = (1/t off )(2 i out /i lpk )/eff where: i out = load current, eff = estimated boost efficien - cy (0.75), i lpk = inductor peak current (350ma), and t off is time needed to discharge the inductor. the expression for t off is: t off = l x i lpk /(v bst + v diode - v in ) for the typical application circuit: t off = 1h x 350ma/(11.7v + 0.4v - 3.7v) = 41.7ns where: l = 1h, i lpk = 350ma, v bst = 11.7v, v diode = 0.4v, and v in = 3.7v, and t off = 41.7ns: f sw(ma) = 183khz/ma of load current the MAX77231 maximum operating frequency (and hence available output current) is governed by the charge (t on ) and discharge time (t off ) of the inductor. t off is calculated above, but is limited to at least 35ns by an internal timer. t on is calculated below: t on = l x i lpk /v in the maximum possible frequency is: f sw(max) = 1/(t on + t off ) and consequently, typical available output current is: i out(max) = f sw(max) /f sw(ma) for a typical scenario with v in = 3.7v, l ipk = 350ma, and a 1h inductor: t on = l x i lpk /v in = 1h x 350ma/3.7v = 94.6ns f sw(max) = 1/(t on + t off ) = 1/(94.6ns + 41.7ns) = 7.33mhz typical available output current for an 11.2v output (at out) and a 3.7v input is then: i out(max) = f sw(max) /f sw(ma) = 7.33/0.183 = 40ma linear regulator the boost is followed by an 11.2v linear regulator. this regulator passes the boost output current to the load, while rejecting the unwanted ripple and reducing noise. the linear regulator can deliver 10ma of output current and provides 50db of ripple rejection at 1mhz. the linear regulator is fed from an internal low-noise reference. the reference voltage is filtered to remove unwanted thermal, shot, and 1/f noise generated in the preceding circuitry. using this low-noise reference, the linear regulator output is able to achieve 35v rms noise in a 100khz bandwidth. maxim integrated 7 MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator www.maximintegrated.com
maxim integrated 8 block diagram (fpo) r 3 r 2 r 1 r 3 r 5 lx 1 h bstp lx pgnd c in 2 . 2 f 6 . 3 v v 1 35 mv 1 . 25 v dly q qb s r dly m 3 m 1 m 2 startup m 4 d 2 5 . 5 v bst out c 1 c out 2 . 2 f 25 v v out = 11 . 2 v 0 ma C 6 ma in enm ens gnd high = on high = on c bst 2 . 2 f 25 v v in = 2 . 7 v to 4 . 8 v 1 . 25 v enm ens bias d 1 max 77231 MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator www.maximintegrated.com
enable/active discharge the MAX77231 has two enable inputs: enm and ens. to turn on the device, both enm and ens must be high. a logic-low on enm disables the device with a 15ma active discharge current. a logic-low on ens disables the device without active discharge. enm and ems functionality is outlined in table 1 . overload and short-circuit protection the MAX77231 is fully protected against output short cir - cuits. in the case of a short circuit, off time is lengthened to prevent inductor current from climbing. the MAX77231 sources current into the short indefinitely, without dam - age, until the short is removed. note, however, that only out, not bst, is protected. a short of v bst can cause inductor and lx current to rise above guaranteed operating levels. component selection input and output capacitance the MAX77231 operates with small ceramic capacitors. x5r or x7r dielectrics are recommended. c in should be 2.2f 6.3v, while c out and c bst should be 2.2f 25v rated. it is expected that the elevated voltage on c out and c bst significantly derate the realized capacitance value at these nodes. the MAX77231 is designed with this expectation and can tolerate a minimum of 0.22f at c out and c bst after derating. inductors the MAX77231 is designed to operate with a 1h 400mh rated inductor. other values up to 10h can be used, but it is expected that in the space-constrained applica - tions for which the MAX77231 is likely to chosen, smaller values are preferred. inductance less than 1h is not recommended because the accompanying higher di/dt can exceed the current comparators ability to effectively limit current. table 1. MAX77231 enable truth table maxim integrated 9 enm ens power state active discharge 0 x power-down on 1 0 power-down off 1 1 active off ordering information chip information process: bicmos package information for the latest package outline information and land patterns (footprints), go to www.maximintegrated.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 the package regardless of rohs status. part temp range pin-package MAX77231ezl+ -40c to +85c 9 wlp package type package code outline no. land pattern no. 9 ultra-thin wlp z91a1+1 21-0691 refer to application note 1891 MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator www.maximintegrated.com
? 2016 maxim integrated products, inc. 10 revision history revision number revision date description pages changed 0 9/15 initial release 1 12/15 corrected typo in block diagram 8 2 5/16 updated boost converter section 7 maxim integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim integrated product. no circuit patent licenses are implied. maxim integrated reserves the right to change the circuitry and specifcations without notice at any time. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. maxim integrated and the maxim integrated logo are trademarks of maxim integrated products, inc. MAX77231 2.75v to 4.8v input, 10ma output, 35v rms ultra-low noise boost regulator for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim integrateds website at www.maximintegrated.com.
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