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_______________general description the max1705/max1706 are high-efficiency, low-noise, step-up dc-dc converters with an auxiliary linear- regulator output. these devices are intended for use in battery-powered wireless applications. they use a syn- chronous rectifier pulse-width-modulation (pwm) boost topology to generate 2.5v to 5.5v outputs from battery inputs, such as 1 to 3 nicd/nimh cells or 1 li-ion cell. the max1705 has an internal 1a n-channel mosfet switch. the max1706 has a 0.5a switch. both devices also have a built-in low-dropout linear regulator that delivers up to 200ma. with an internal synchronous rectifier, the max1705/ max1706 deliver 5% better efficiency than similar non- synchronous converters. they also feature a pulse- frequency-modulation (pfm) standby mode to improve efficiency at light loads, and a 1? shutdown mode. an efficiency-enhancing track mode reduces the step-up dc-dc converter output to 300mv above the linear-reg- ulator output. both devices come in a 16-pin qsop package, which occupies the same space as an 8-pin so. other features include two shutdown-control inputs for push-on/push-off control, and an uncommitted comparator for use as a volt- age monitor. ________________________applications digital cordless phones pcs phones personal communicators wireless handsets palmtop computers two-way pagers hand-held instruments ____________________________features ? up to 96% efficiency ? 1.1v in guaranteed start-up ? up to 850ma output (max1705) ? step-up output (2.5v to 5.5v adjustable) ? linear regulator (1.25v to 5.0v adjustable) ? pwm/pfm synchronous-rectified topology ? 300khz pwm mode or synchronizable ? 1? shutdown mode ? voltage monitor ? pushbutton on/off control max1705/max1706 1- to 3-cell, high-current, low-noise, step-up dc-dc converters with linear regulator ________________________________________________________________ maxim integrated products 1 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 lbp pout ona onb lx pgnd clk/sel lbo ldo top view max1705 max1706 qsop lbn ref out track gnd fb fbldo __________________pin configuration lx pout out step-up output fb clk/sel ona onb track input 0.7v to 5.5v pgnd gnd ldo fbldo lbp lbo lbn ref max1705 max1706 linear regulator output low-battery detection on/off control high efficiency low noise __________typical operating circuit 19-1198; rev 0; 4/97 part max1705 c/d max1705eee max1706 c/d 0? to +70? -40? to +85? 0? to +70? temp. range pin-package dice* 16 qsop dice* evaluation kit manual available ______________ordering information * dice are tested at t a = +25?, dc parameters only. for free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 max1706eee -40? to +85? 16 qsop
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v out = v pout = v lbp = 3.6v, clk/sel = fb = lbn = lbo = ona = onb = track = gnd, ref = open (bypassed with 0.22 f), lx = open, t a = 0 c to +85 c, unless otherwise noted. typical values are at t a = +25 c.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. ona, onb , fbldo, out, pout to gnd ................... -0.3v to 6v pgnd to gnd ..................................................................... 0.3v pout to out ...................................................................... 0.3v lx to pgnd ............................................ -0.3v to (v pout + 0.3v) clk/sel, ref, fb, track, ldo, lbn, lbp, lbo to gnd ....................... -0.3v to (v out + 0.3v) ldo short circuit ....................................................... continuous continuous power dissipation (t a = +70 c) qsop (derate 8.70mw/ c above +70 c) ................... 696mw operating temperature range ........................... -40 c to +85 c junction temperature ...................................................... +150 c storage temperature range ............................. -65 c to +160 c lead temperature (soldering, 10sec) ............................. +300 c clk/sel = out -1 a < i ref < 50 a (note 1) i ref = 0 a clk/sel = gnd, v fb = v fbldo = 1.5v, no load ona = gnd, onb = out, measure i out (note 2) v pout = v out = 1.5v v fb = 1.5v max1705, 0a i lx 0.5a; max1706, 0a i lx 0.25a; clk/sel = out track = v ldo > 2.3v clk/sel = out conditions mv 4 15 reference load regulation v 1.238 1.250 1.262 reference output voltage a 180 360 i out supply current in low-noise mode v 1.219 1.233 1.247 fb regulation voltage v 0.7 minimum operating battery voltage a 100 190 i out supply current in low-power mode a 1 20 i out supply current in shutdown v 2.00 2.15 2.30 start-up to normal mode transition voltage khz 40 150 300 f lx frequency in start-up mode na 0.01 50 fb input current v 2.5 5.5 out adjust range % 0.65 1.25 load regulation v v ldo v ldo v ldo + 0.2 + 0.3 + 0.4 out voltage in track mode units min typ max symbol parameter t a = +25 c, i load < 1ma, figure 2 v 0.9 1.1 minimum start-up voltage 2.5v < v out < 5.5v mv 0.2 5 reference supply regulation dc-dc converter reference v fb = v fbldo = 1.5v, no load fb = gnd (lx switching) 2.1 ma
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator _______________________________________________________________________________________ 3 electrical characteristics (continued) (v out = v pout = v lbp = 3.6v, clk/sel = fb = lbn = lbo = ona = onb = track = gnd, ref = open (bypassed with 0.22 f), lx = open, t a = 0 c to +85 c, unless otherwise noted. typical values are at t a = +25 c.) f = 300khz v out = 5.5v, clk/sel, track v lbo = v out = 5v i sink = 1ma, v out = 2.5v, lbp = gnd, lbn = out 1.2v < v out < 5.5v, ona, onb (note 3) v out = 2.5v, clk/sel, track v lbn = v lbp = 1v v lbn = 0.5v and 1.5v (at least one input must be within this range) hysteresis approximately 10 c lbp falling 1.2v < v out < 5.5v, ona, onb (note 3) lbp rising conditions a 1 input leakage current (clk/sel, ona, onb , track) 0.8v out v 0.8v out input high level 0.2v out v 0.2v out input low level db 38 ac power-supply rejection a 1 lbo high leakage v 0.4 lbo output low voltage na 0.01 50 lbn, lbp input current v 0.5 1.5 lbn, lbp common-mode input range c 155 thermal shutdown mv -5 5 lbn, lbp offset mv 16 lbn, lbp hysteresis units min typ max symbol parameter ma 20 70 120 p-channel synchronous- rectifier turn-off current v lx = 0v, v onb = v out = 5.5v a 0.1 20 pout leakage current clk/sel = gnd clk/sel = gnd 250 435 550 clk/sel = out ma 1000 1280 1550 i lim n-channel mosfet current limit 550 750 950 max1705 max1705 max1706 max1706 250 435 550 fbldo = ldo, i load = 1ma v 1.238 1.250 1.262 fbldo regulation voltage v fbldo = 1.5v na 0.01 50 fbldo input current fbldo = gnd ma 220 300 500 short-circuit current limit v fbldo = 1v, i ldo = 200ma w 0.5 1.2 dropout resistance 10 a < i ldo < 200ma, fbldo = ldo % 0.4 1.2 load regulation 2.5v < v out < 5.5v, fbldo = ldo, i ldo = 1ma % 0.1 0.5 line regulation p-channel, i lx = 100ma 0.27 0.50 n-channel, i lx = 100ma w 0.23 0.45 switch on-resistance 0.16 0.28 clk/sel = gnd clk/sel = out v lx = 0v, v onb = v out = 5.5v a 0.1 20 lx leakage current v 1.25 5.0 ldo adjust range control inputs low-battery comparator linear regulator dc-dc switches
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 4 _______________________________________________________________________________________ electrical characteristics (continued) (v out = v pout = v lbp = 3.6v, clk/sel = fb = lbn = lbo = ona = onb = track = gnd, ref = open (bypassed with 0.22 f), lx = open, t a = 0 c to +85 c, unless otherwise noted. typical values are at t a = +25 c.) electrical characteristics (v out = v pout = v lbp = 3.6v, clk/sel = fb = lbn = lbo = ona = onb = track = gnd, ref = open (bypassed with 0.22 f), lx = open, t a = -40 c to +85 c, unless otherwise noted, note 4.) parameter symbol min typ max units minimum clk/sel pulse internal oscillator frequency 260 300 340 khz 200 ns maximum clk/sel rise/fall time 100 ns conditions clk/sel = out supply current in low-power mode i out 190 a clk/sel = 0v, fb = fbldo = 1.5v, no load supply current in shutdown i out 20 a ona = 0v, onb = out, measure i out out voltage in track mode v ldo + v ldo + 0.2 0.4 v track = out, v ldo > 2.3v 250 570 max1706 max1706 clk/sel = out clk/sel = 0v max1705 clk/sel = out clk/sel = 0v 0.28 max1705 switch on-resistance 0.45 n-channel, i lx = 100ma 550 950 n-channel mosfet current limit i lim 1000 1700 ma clk/sel = out 250 570 0.50 clk/sel = 0v p-channel, i lx = 100ma parameter symbol min typ max p-channel synchronous- rectifier turn-off current units conditions 20 120 ma start-up to normal mode transition voltage 2.0 2.3 v fb regulation voltage 1.215 1.251 v clk/sel = out reference output voltage 1.235 1.265 v i ref = 0 a oscillator maximum duty cycle 80 86 90 % external oscillator synchronization range 200 400 khz supply current in low-noise mode i out 360 a clk/sel = out, v fb = v fbldo = 1.5v, no load dc-dc converter reference dc-dc converter
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator _______________________________________________________________________________________ 5 electrical characteristics (continued) (v out = v pout = v lbp = 3.6v, clk/sel = fb = lbn = lbo = ona = onb = track = gnd, ref = open (bypassed with 0.22 f), lx = open, t a = -40 c to +85 c, unless otherwise noted, note 4.) parameter symbol min typ max units lbn, lbp common-mode input range 0.5 1.5 v conditions lbn = 0.5v and 1.5v (at least one input must be within this range) lbo high leakage 1 a lbo = out = 5v input low level 0.15v out v 1.2v < v out < 5.5v, ona, onb (note 2) 0.85v out 1.2v < v out < 5.5v, ona, onb (note 2) internal oscillator frequency 260 340 khz clk/sel = out external oscillator synchronization range 200 400 khz 0.85v out v out = 5.5v, clk/sel, track note 1: once the output is in regulation, the max1705/max1706 operate down to a 0.7v input voltage. note 2: the device is in start-up mode when v out is below this value (see low-voltage start- u p oscillator section). note 3: ona and onb inputs have a hysteresis of approximately 0.15v out . note 4: specifications to -40 c to are guaranteed by design, not production tested. input high level v out = 2.5v, clk/sel, track 0.15v out v lbn, lbp offset -5 5 mv lbp falling fbldo regulation voltage 1.233 1.268 v fbldo = ldo, i load = 1ma short-circuit current limit 220 600 ma fbldo = ldo = gnd fbldo input current 0.01 50 na v fbldo = 1.5v dropout resistance 1.2 v fbldo = 1v, i ldo = 200ma linear regulator control inputs low-battery comparator
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 6 _______________________________________________________________________________________ __________________________________________ t ypical operating characteristics (circuit of figure 2, t a = +25 c, unless otherwise noted.) 100 0 0.1 10 100 1 1000 max1705 efficiency vs. output current (v out = 5v) 20 max1705/6 toc02 output current (ma) efficiency (%) 40 60 80 90 10 30 50 70 l = 10 m h v out = 5v a: v in = 0.9v c: v in = 2.4v e: v in = 3.6v 1: pfm mode 2: pwm mode a.1 a.2 c.1 c.2 b.2 b.1 100 0 0.1 10 100 1 1000 max1705 efficiency vs. output current (v out = 3.3v) 20 max1705/6 toc01 output current (ma) efficiency (%) 40 60 80 90 10 30 50 70 l = 10 m h v out = 3.3v a: v in = 0.9v b: v in = 2.7v 1: pfm mode 2: pwm mode b.1 b.2 a.1 a.2 0 0 max1705 maximum output current vs. input voltage 200 100 300 max1705/6 toc03 input voltage (v) maximum output current (ma) 3.5 700 600 900 800 400 500 1.0 2.5 4.5 1000 2.0 3.0 0.5 4.0 1.5 l = 10 m h pwm mode pfm mode v out = 3.3v v out = 3.3v v out = 5v v out = 5v 100 0 0.1 10 100 1 1000 max1706 efficiency vs. output current (v out = 3.3v) 20 max1705/6 toc04 output current (ma) efficiency (%) 40 60 80 90 10 30 50 70 b.2 a.2 a.1 b.1 l = 22 m h v out = 3.3v a: v in = 0.9v b: v in = 2.7v 1: pfm mode 2: pwm mode 0.5 0.01 max1705 start-up input voltage vs. output current 0.9 0.7 1.1 max1705/6 toc07 output current (ma) start-up input voltage (v) 100 1.7 1.5 2.1 1.9 1.3 0.1 10 1000 2.3 1 no-load start-up: 1.0v at -40? 0.79 at +25? 0.64v at +85? constant-current load v out = 3.3v l = 10 m h d1 = mbr0520l t a = -40? t a = +25? t a = +85? 100 0 0.1 10 100 1 1000 max1706 efficiency vs. output current (v out = 5v) 20 max1705/6 toc05 output current (ma) efficiency (%) 40 60 80 90 10 30 50 70 a.1 a.2 c.2 b.2 c.1 b.1 l = 22 m h v out = 5v a: v in = 0.9v b: v in = 2.4v c: v in = 3.6v 1: pfm mode 2: pwm mode 0 0 max1706 maximum output current vs. input voltage 200 100 300 max1705/6 toc06 input voltage (v) maximum output current (ma) 3.5 700 600 400 500 1.0 3 4.5 2.0 0.5 2.5 4 1.5 pwm mode l = 22 m h pfm mode v out = 5v v out = 5v v out = 3.3v v out = 3.3v 0 0 no-load supply current vs. input voltage 2 1 3 max1705/6 toc8 input voltage (v) no-load supply current (ma) 4.0 7 6 10 9 8 4 5 1.0 3.0 5.0 12 11 2.0 3.5 0.5 2.5 4.5 1.5 pfm mode pwm mode v out = 3.3v l = 10 m h 0 0 linear-regulator dropout voltage vs. load current 20 40 max1705/6 toc09 load current (ma) dropout voltage (mv) 160 120 100 60 80 40 120 200 140 80 v ldo = 3.3v v ldo = 2.5v v ldo = 5v
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator _______________________________________________________________________________________ 7 ____________________________ t ypical operating characteristics (continued) (circuit of figure 2, t a = +25 c, unless otherwise noted.) 60 0 100 10k 100k 1m 1k 10m linear-regulator power-supply rejection ratio vs. frequency 10 20 max1705/6 toc10 frequency (hz) psrr (db) 30 50 40 v out = 4v to 5v v ldo = 3.3v i ldo = 200ma c5 = 0.33 m f 100 0 1 100 50 200 250 150 300 linear-regulator region of stable c6 esr vs. load current 0.1 max1705/6 toc11 load current (ma) c6 esr ( w ) 1 10 stable region c2 = 22pf (feed forward) uncompensated c6 = 22 m f 1k 10k 100k 1m 10m max1705 noise spectrum at pout (v out = 4.5v, v in = 1.2v, 200ma load) 0v max1705/6 toc13 frequency (hz) noise (5mv rms/ div) 1k 10k 100k 1m 10m max1705 linear-regulator output noise spectrum (v ldo = 3.3v, v out = 4.5v, v in = 1.2v, i ldo = 200ma) 0v max1705/6 toc14 frequency (hz) noise (50 m v/div)
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 8 _______________________________________________________________________________________ ____________________________ t ypical operating characteristics (continued) (circuit of figure 2, t a = +25 c, unless otherwise noted.) 200 m s/div max1705 line-transient response max1705/6 toc15 i out = 0ma, v out = 3.3v a = v in , 1.5v to 2.0v, 200mv/div b = v out, 10mv/div, 3.3v dc offset a b 200 m s/div max1705 power-on delay (pwm mode) max1705/6 toc17 v in = 1.2v, load = 1k w a = ona, 2v/div b = v ldo , 2v/div c = v out , 2v/div d = inductor current, 500ma/div a c d 3v 2.5v 3.3v 0ma b 1 m s/div max1705 pwm switching waveforms max1705/6 toc18 v in = 1.2v, v out = 4.5v, v ldo = 3.3v, i ldo = 200ma a = inductor current, 500ma/div b = lx voltage, 5v/div c = v out ripple, 50m/div ac coupled d = v ldo ripple, 5m/div ac coupled c5 = 0.33 m f a b d c 0v 1a v out v ldo 2 m s/div max1705 pfm switching waveforms max1705/6 toc19 v in = 1.2v, v out = 4.5v, v ldo = 3.3v, i ldo = 40ma a = inductor current, 500ma/div b = lx voltage, 5v/div c = v out ripple, 50mv/div ac coupled d = v ldo ripple, 5mv/div ac coupled c5 = 0.33 m f a c d 0ma 0v v out v ldo b 1ms/div max1705 linear-regulator output noise max1705/6 toc20 v ldo is ac coupled, 1mv/div i ldo = 200ma c5 = 0.33 m f v ldo dc to 500khz 200 m s/div max1705 load-transient response max1705/6 toc16 v in = 1.2v, v out = 3.3v a = v out , 50mv/div, 3.3v dc offset b = i out , 0ma to 200ma, 200ma/div a b
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator _______________________________________________________________________________________ 9 ______________________________________________________________ pin description boost dc-dc converter power output. pout is the source of the p-channel synchronous-rectifier mosfet switch. connect an external schottky diode from lx to pout. the output current available from pout is reduced by the current drawn from the ldo linear-regulator output. pout 16 on control input. when ona = high or onb = low, the ic turns on. connect ona to out for normal operation (table 2). ona 15 off control input. when onb = high and ona = low, the ic is off. connect onb to gnd for normal operation (table 2). onb 14 inductor connection to the drains of the p-channel synchronous rectifier and n-channel switch lx 13 power ground for the source of the n-channel power mosfet switch pgnd 12 low-dropout linear-regulator output. ldo sources up to 200ma. bypass to gnd with a 22 f capacitor. ldo 9 low-battery comparator output. this open-drain, n-channel output is low when lbp < lbn. input hysteresis is 16mv. lbo 10 switching-mode selection and external-clock synchronization input: ? clk/sel = low: low-power, low-quiescent-current pfm mode. ? clk/sel = high: low-noise, high-power pwm mode. switches at a constant frequency (300khz). full output power is available. clk/sel = driven with an external clock: low-noise, high-power synchronized pwm mode. synchronizes to an external clock (from 200khz to 400khz). turning on the dc-dc converter with clk/sel = gnd also serves as a soft-start function, since peak inductor current is reduced. clk/sel 11 ground gnd 5 step-up converter feedback input, used during track mode. ic power and low-dropout linear-regulator input. bypass out to gnd with a 0.1 f ceramic capacitor placed as close to the ic as possible. out 6 step-up dc-dc converter feedback input. connect fb to a resistor voltage divider between pout and gnd to set the output voltage between 2.5v and 5.5v. fb regulates to 1.233v. fb 7 low-dropout linear-regulator feedback input. connect fbldo to a resistor voltage divider between ldo to gnd to set the output voltage from 1.25v to v out - 0.3v (5.0v max). fbldo regulates to 1.250v. fbldo 8 track-mode control input for dc-dc converter. in track mode, the boost-converter output is sensed at out and set 0.3v above ldo to improve efficiency. set track to out for track mode. connect track to gnd for normal operation. track 4 1.250v reference output. bypass ref with a 0.33 f capacitor to gnd. ref can source up to 50 a. ref 3 pin low-battery comparator inverting input. common-mode range is 0.5v to 1.5v. lbn 2 low-battery comparator noninverting input. common-mode range is 0.5v to 1.5v. lbp 1 function name
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 10 ______________________________________________________________________________________ _______________ detailed description the max1705/max1706 are designed to supply both power and low-noise circuitry in portable rf and data- acquisition instruments. they combine a linear regula - tor, step-up switching regulator, n-channel power mosfet, p-channel synchronous rectifier, precision reference, and low-battery comparator in a single 16- pin qsop package (figure 1). the switching dc-dc converter boosts a 1- or 2-cell input to an adjustable output between 2.5v and 5.5v. the internal low-dropout regulator provides linear post-regulation for noise- sensitive circuitry, as well as outputs from 1.25v to 300mv below the switching-regulator output. the max1705/max1706 start from a low, 1.1v input and remain operational down to 0.7v. these devices are optimized for use in cellular phones and other applications requiring low noise during full- power operation, as well as low quiescent current for maximum battery life during standby and shutdown. they feature constant-frequency (300khz), low-noise pulse-width-modulation (pwm) operation with 300ma or 730ma output capability from one or two cells, respec - tively, with 3.3v output. a low-quiescent-current stand - by pulse-frequency-modulation (pfm) mode offers an output up to 60ma and 140 a, respectively, and reduces quiescent power consumption to 500 w. in shutdown mode, the quiescent current is further reduced to just 1 a. figure 2 shows the standard appli - cation circuit for the max1705 configured in high- power pwm mode. additional features include synchronous rectification for high efficiency and improved battery life, and an uncommitted comparator for low-battery detection. a clk/sel input allows frequency synchronization to reduce interference. dual shutdown controls allow shut - down using a momentary pushbutton switch and micro - processor control. lbp fbldo out 2.15v ona on onb ref gnd clk/sel fb ldo pout lx pgnd lbo lbn ref shutdown logic thermal sensor max1705 max1706 error amp st ar t -up oscilla tor en q p p n mosfet driver with current limiting en 300khz oscilla tor en d osc mode pfm/pwm q q ifb pfm/pwm controller n rdy 1.250v reference track ic pwr iref v out - 300mv v ldo ics out figure 1. functional diagram
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator ______________________________________________________________________________________ 11 step-up converter the step-up switching dc-dc converter generates an adjustable output to supply both power circuitry (such as rf power amplifiers) and the internal low-dropout linear regulator. during the first part of each cycle, the internal n-channel mosfet switch is turned on. this allows current to ramp up in the inductor and store energy in a magnetic field. during the second part of each cycle, when the mosfet is turned off, the voltage across the inductor reverses and forces current through the diode and synchronous rectifier to the out - put filter capacitor and load. as the energy stored in the inductor is depleted, the current ramps down, and the output diode and synchronous rectifier turn off. voltage across the load is regulated using either pwm or pfm operation, depending on the clk/sel pin set - ting (table 1). low-noise, high-power pwm operation when clk/sel is pulled high, the max1705/max1706 operate in a high-power, low-noise pwm mode. during pwm operation, they switch at a constant frequency (300khz), and modulate the mosfet switch pulse width to control the power transferred per cycle and regulate the voltage across the load. in pwm mode, the devices can output up to 850ma. switching harmonics generated by fixed-frequency operation are consistent and easily filtered. during pwm operation, each of the internal clock? ris - ing edges sets a flip-flop, which turns on the n-channel mosfet switch (figure 3). the switch is turned off when the sum of the voltage-error and current- feedback signals trips a multi-input comparator and resets the flip-flop; the switch remains off for the rest of the cycle. when a change occurs in the output voltage error signal into the comparator, it shifts the level that the inductor current is allowed to ramp to during each cycle and modulates the mosfet switch pulse width. a second comparator enforces a 1.55a (max) inductor- lx pout out boost output 3.6v fb ldo output 3.3v input 0.9v to 3.6v (to pgnd) (to pgnd) pgnd gnd ldo fbldo lbo lbn ref max1705 max1706 lbp clk/sel ona onb track r3 165k r4 100k r5 r6 r7 100k c2* d1 c7 22 m f c8 0.33 m f l1 10 m h (22 m h) *optional. ( ) are for max1706. c4 220 m f (100 m f) c5* 0.33 m f c6 22 m f r1 191k c3 0.1 m f c9 0.33 m f c1* r2 100k note: hea vy lines indica te high-current p a th. figure 2. typical operating circuit (pwm mode) clk/sel mode features 0 pfm low supply current 1 pwm low noise, high output current external clock (200khz to 400khz) synchronized pwm low noise, high output current table 1. selecting the operating mode
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 12 ______________________________________________________________________________________ current limit for the max1705, and 950ma (max) for the max1706. during pwm operation, the circuit operates with a continuous inductor current. synchronized pwm operation the max1705/max1706 can also be synchronized to a 200khz to 400khz frequency by applying an external clock to clk/sel. this allows the user to set the har - monics, to avoid if bands in wireless applications. the synchronous rectifier is also active during synchronized pwm operation. low-power pfm operation pulling clk/sel low places the max1705/max1706 in low-power standby mode. during standby mode, pfm operation regulates the output voltage by transferring a fixed amount of energy during each cycle, and then modulating the switching frequency to control the power delivered to the output. the devices switch only as needed to service the load, resulting in the highest possible efficiency at light loads. output current capa - bility in pfm mode is 140ma (from 2.4v input to 3.3v output). the output is regulated at 1.3% above the pwm threshold. during pfm operation, the error comparator detects output voltage falling out of regulation and sets a flip-flop, turning on the n-channel mosfet switch (figure 4). when the inductor current ramps to the pfm mode current limit (435ma) and stores a fixed amount of energy, the current-sense comparator resets a flip- flop. the flip-flop turns off the n-channel switch and turns on the p-channel synchronous rectifier. a second flip-flop, previously reset by the switch? ?n?signal, inhibits the error comparator from initiating another cycle until the energy stored in the inductor is dumped into the output filter capacitor and the synchronous rec - tifier current ramps down to 70ma. this forces opera - tion with a discontinuous inductor current. synchronous rectifier the max1705/max1706 feature an internal 270m , p-channel synchronous rectifier to enhance efficiency. synchronous rectification provides a 5% efficiency improvement over similar nonsynchronous step-up regulators. in pwm mode, the synchronous rectifier is turned on during the second half of each cycle. in pfm mode, an internal comparator turns on the synchronous rectifier when the voltage at lx exceeds the step-up converter output, and then turns it off when the inductor current drops below 70ma. linear regulator the internal low-dropout linear regulator steps down the output from the step-up converter and reduces switching ripple. it is intended to power noise-sensitive analog cir - cuitry, such as low-noise amplifiers and if stages in cel - lular phones and other instruments, and can deliver up to 200ma. however, in practice, the maximum output cur - rent is further limited by the current available from the boost converter and by the voltage differential between out and ldo. use a 22 f capacitor with a 1 or less equivalent series resistance (esr) at the output for sta - bility (see the linear regulator region of stable c6 esr vs. load current graph in the typical operating characteristics ). during power-up, the linear regulator remains off until the step-up converter goes into regula - tion for the first time. pout lx pgnd p n s q ics r ifb* iref* current limit level osc *see figure 1 n lx pgnd ifb* iref* current limit level s q r q q r d logic high pout p *see figure 1 figure 3. simplified pwm controller block diagram figure 4. controller block diagram in pfm mode
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator ______________________________________________________________________________________ 13 the linear regulator in the max1705/max1706 features a 0.5 , p-channel mosfet pass transistor. this pro - vides several advantages, including longer battery life, over similar designs using a pnp pass transistor. the p-channel mosfet requires no base-drive current, which reduces quiescent current considerably. pnp- based regulators tend to waste base-drive current in dropout when the pass transistor saturates. the max1705/max1706 eliminate this problem. the linear-regulator error amplifier compares the output feedback sensed at the fbldo input against the inter - nal 1.250v reference, and amplifies the difference (figure 1). the mosfet driver reads the error signal and applies the appropriate drive to the p-channel pass transistor. if the feedback signal is lower than the reference, the pass-transistor gate is pulled lower, allowing more current to pass to the output, thereby increasing the output voltage. if the feedback voltage is too high, the pass-transistor gate is pulled up, allowing less current to pass to the output. additional blocks include a current-limiting block and a thermal-overload protection block. low-voltage start-up oscillator the max1705/max1706 use a cmos, low-voltage start-up oscillator for a 1.1v guaranteed minimum start- up input voltage at +25 c. on start-up, the low-voltage oscillator switches the n-channel mosfet until the out - put voltage reaches 2.15v. above this level, the normal step-up converter feedback and control circuitry take over. once the device is in regulation, it can operate down to a 0.7v input, since internal power for the ic is bootstrapped from the output using the out pin. to reduce current loading during step-up, the linear regulator is kept off until the start-up converter goes into regulation. minimum start-up voltage is influenced by load and temperature (see the typical operating characteristics ). to allow proper start-up, do not apply a full load at pout until after the device has exited start-up mode and entered normal operation. shutdown the max1705/max1706 feature a shutdown mode that reduces quiescent current to less than 1 a, preserving battery life when the system is not in use. during shut - down, the reference, the low-battery comparator, and all feedback and control circuitry are off. the step-up converter? output drops to one schottky diode drop below the input, but the linear regulator output is turned off. entry into shutdown mode is controlled by logic input pins ona and onb (table 2). both inputs have trip points near 0.5v out with 0.15v out hysteresis. tracking connecting track to the step-up converter output implements a tracking mode that sets the step-up converter output to 300mv above the linear-regulator output, improving efficiency. in track mode, feedback for the step-up converter is derived from the out pin. when track is low, the step-up converter and linear regulator are separately controlled by their respective feedback inputs, fb and fbldo. track is a logic input with a 0.5v out threshold, and should be hard- wired or switched with a slew rate exceeding 1v/ s. v ldo must be set above 2.3v for track mode to operate properly. on power-up with track = out, the step-up convert - er initially uses the fb input to regulate its output. after the step-up converter goes into regulation for the first time, the linear regulator turns on. when the linear regu - lator reaches 2.3v, track mode is enabled and the step- up converter is regulated to 300mv above the linear- regulator output. low-battery comparator the internal low-battery comparator has uncommitted inputs and an open-drain output capable of sinking 1ma. to use it as a low-battery-detection comparator, connect the lbn input to the reference, and connect the lbp input to an external resistor divider between the positive battery terminal and gnd (figure 2). the resistor values are then as follows: where v in,th is the desired input voltage trip point and v lbn = v ref = 1.25v. since the input bias current into lbp is less than 50na, r6 can be a large value (such as 270k or less) without sacrificing accuracy. connect the resistor voltage divider as close to the ic as possible, within 0.2in. (5mm) of the lbp pin. the inputs have a 0.5v to 1.5v common-mode input range, and a 16mv input-referred hysteresis. r r v v in th lbn 5 6 , = ? ? ? ? - 1 ona onb max1705/max1706 0 0 on 0 1 off 1 0 on 1 1 on table 2. on/off logic control
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 14 ______________________________________________________________________________________ the low-battery comparator can also be used to moni - tor the output voltage, as shown in figure 5. to set the low-battery threshold to a voltage below the 1.25v reference, insert a resistor divider between ref and lbn, and connect the battery to the lbp input through a 10k current-limiting resistor (figure 6). the equation for setting the resistors for the low-battery threshold is then as follows: alternatively, the low-battery comparator can be used to check the output voltage or to control the load direct - ly on pout during start-up (figure 7). use the following equation to set the resistor values: where v out,th is the desired output voltage trip point and v lbp is connected to the reference or 1.25v. reference the max1705/max1706 have an internal 1.250v, 1% bandgap reference. connect a 0.33 f bypass capaci - tor to gnd within 0.2in. (5mm) of the ref pin. ref can source up to 50 a of external load current. _________________ design pr ocedur e setting the output voltages set the step-up converter output voltage between 2.5v and 5.5v by connecting a resistor voltage-divider to fb from out to gnd, as shown in figure 8. the resistor values are then as follows: where v fb , the step-up regulator feedback setpoint, is 1.233v. since the input bias current into fb is less than 50na, r2 can have a large value (such as 270k or less) without sacrificing accuracy. connect the resistor voltage-divider as close to the ic as possible, within 0.2in. (5mm) of the fb pin. alternatively, set the step-up converter output to track the linear regulator by 300mv. to accomplish this, set track to out. r r v v pout fb 1 2 = ? ? ? ? - 1 r r v v out th lbp 5 6 , = ? ? ? ? - 1 r r v v ref in th 5 6 , = ? ? ? ? - 1 max1705 max1706 lbo ref lbn pout gnd r5 r6 0.33 m f ldo lbp max1705 max1706 lbn lbo lbp pout ref gnd r5 r6 ba tter y vol t age r8 10k 0.33 m f 270k max1705 max1706 lbp lbo lbn 0.33 m f out pout ref gnd r5 r6 p c3 0.1 m f c4 c5 step-up output figure 5. using the low-battery comparator to sense the output voltage figure 6. detecting battery voltages below 1.25v figure 7. using the low-battery comparator for load control during start-up
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator ______________________________________________________________________________________ 15 to set the low-dropout linear-regulator output, use a resistor voltage-divider connected to fbldo from ldo to gnd. set the output to a value at least 300mv less than the step-up converter output using the following formula: where v fbldo , the linear-regulator feedback trip point, is 1.250v. since the input bias current into fbldo is less than 50na, r4 can be a large value (such as 270k or less). connect the resistor voltage-divider as close to the ic as possible, within 0.2in. (5mm) of the fbldo pin. inductor selection the max1705/max1706? high switching frequency allows the use of a small surface-mount inductor. use a 10 h inductor for the max1705 and a 22 h inductor for the max1706. make sure the saturation-current rat - ing exceeds the n-channel switch current limit of 1.55a for the max1705 and 950ma for the max1706. for high efficiency, chose an inductor with a high-frequency core material, such as ferrite, to reduce core losses. to minimize radiated noise, use a torroid, pot core, or shielded-bobbin inductor. see table 3 for suggested parts and table 4 for a list of inductor suppliers. connect the inductor from the battery to the lx pin as close to the ic as possible. attaching the output diode use a schottky diode, such as a 1n5817, mbr0520l, or equivalent. the schottky diode carries current during start-up, and in pfm mode after the synchronous rectifi - er turns off. thus, the current rating only needs to be 500ma. attach the diode between the lx and pout pins, as close to the ic as possible. in high-temperature applications, some schottky diodes may be unsuitable due to high reverse-leakage currents. try substituting a schottky diode with a higher reverse voltage rating, or use an ultra-fast silicon rectifi - er with reverse recover times less than 60ns (such as a mur150 or ec11fs1). do not use ordinary rectifier diodes, since slow switching speeds and long re- verse recovery times compromise efficiency and load regulation. choose input and output filter capacitors choose input and output filter capacitors that service the input and output peak currents with acceptable voltage ripple. choose input capacitors with working voltage ratings over the maximum input voltage, and output capacitors with working voltage ratings higher than the output. a 100 f, 100m , low-esr tantalum capacitor is recom - mended at the max1706? step-up output. for the max1705, use two in parallel or a 220 f low-esr tanta - lum capacitor. the input filter capacitor (c7) also reduces peak currents drawn from the input source and reduces input switching noise. the input voltage source impedance determines the size required for the input capacitor. when operating directly from one or two nicd cells placed close to the max1705/max1706, use a 22 f, low-esr input filter capacitor. when operating from a power source placed farther away, or r r v v ldo fbldo 3 4 = ? ? ? ? - 1 out pout fb fbldo ldo gnd pgnd max1705 max1706 step-up output linear- regula tor output r1 r2 r3 r4 c1* c2* * optional compensa tion cap acitors figure 8. feedback connections for the max1705/max1706 production inductors capacitors diodes surface mount sumida cdr63b, cd73, cdr73b, cd74b series coilcraft do1608, do3308, dt3316 series matsuo 267 series sprague 595d series avx tps series motorola mbr0520l through hole sumida rch654 series sanyo os-con series nichicon pl series motorola 1n5817 table 3. component selection guide
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 16 ______________________________________________________________________________________ from higher-impedance batteries, consider using one or two 100 f, 100m , low-esr tantalum capacitors. low-esr capacitors are recommended. capacitor esr is a major contributor to output ripple?ften more than 70%. ceramic, sanyo os-con, and panasonic sp/cb-series capacitors offer the lowest esr. low-esr tantalum capacitors are second best and generally offer a good trade-off between price and performance. do not exceed the ripple-current ratings of tantalum capaci - tors. avoid aluminum-electrolytic capacitors, since their esr is too high. adding bypass capacitors several ceramic bypass capacitors are required for proper operation of the max1705/max1706. bypass ref with a 0.33 f capacitor to gnd. connect a 0.1 f ceramic capacitor from out to gnd and a 0.33 f ceramic capacitor from pout to pgnd. place a 22 f, low-esr capacitor and an optional 0.33 f ceramic capacitor from the linear-regulator output ldo to gnd. an optional 22pf ceramic capacitor can be added to the linear-regulator feedback network to reduce noise (c2, figure 2). place each of these as close to their respective pins as possible, within 0.2in. (5mm) of the dc-dc converter ic. high-value, low-voltage, surface- mount ceramic capacitors are now readily available in small packages; see table 4 for suggested suppliers. designing a pc board high switching frequencies and large peak currents make pc board layout an important part of design. poor design can cause excessive emi and ground- bounce, both of which can cause instability or regulation errors by corrupting voltage- and current- feedback signals. it is highly recommended that the pc board example of the max1705 evaluation kit (ev kit) be followed. power components?uch as the inductor, converter ic, filter capacitors, and output diode?hould be placed as close together as possible, and their traces should be kept short, direct, and wide. place the ldo output capacitor as close to the ldo pin as possible. m ake the connection between pout and out very short. keep the extra copper on the board, and inte - grate it into ground as a pseudo-ground plane. on multilayer boards, do not connect the ground pins of the power components using vias through an internal ground plane. instead, place them close together and route them in a star-ground configuration using compo - nent-side copper. then connect the star ground to the internal ground plane using vias. keep the voltage-feedback networks very close to the max1705/max1706?ithin 0.2in. (5mm) of the fb and fbldo pins. keep noisy traces, such as from the lx pin, away from the reference and voltage-feedback net - works, especially the ldo feedback, and separated from them using grounded copper. consult the max1705/max1706 ev kit for a full pc board example. __________ applications infor mation use in a typical wireless phone application the max1705/max1706 are ideal for use in digital cord - less and pcs phones. the power amplifier (pa) is con - nected directly to the step-up converter output for maximum voltage swing (figure 9). the internal linear regulator is used for post-regulation to generate low- noise power for dsp, control, and rf circuitry. typically, rf phones spend most of their life in standby mode and short periods in transmit/receive mode. during standby, maximize battery life by setting clk/sel = gnd and track = out; this places the ic in pfm and track modes (for lowest quiescent power consumption). in transmit/receive mode, set track = gnd and clk/sel = out to increase the pa supply voltage and initiate high-power, low-noise pwm operation . table 5 lists the typical available output current when operating with one or more nicd/nimh cells or one li-ion cell. table 4. component suppliers (847) 956-0702 81-3-3607-5144 usa: (847) 956-0666 japan: 81-3-3607-5111 sumida (619) 661-1055 81-7-2070-1174 usa: (619) 661-6835 japan: 81-7-2070-6306 sanyo (602) 994-6430 usa: (602) 303-5454 motorola (714) 960-6492 usa: (714) 969-2491 matsuo (847) 639-1469 usa: (847) 639-6400 coilcraft (803) 626-3123 usa: (803) 946-0690 (800) 282-4975 avx fax phone supplier
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator ______________________________________________________________________________________ 17 implementing soft-start to implement soft-start, set clk/sel low on power-up; this forces pfm operation and reduces the peak switch - ing current to 435ma. once the circuit is in regulation, clk/sel can be set high for full-power operation. adding a manual power reset a momentary pushbutton switch can be used to turn the max1705/max1706 on and off (figure 10). ona is pulled low and onb is pulled high to turn the part off. when the momentary switch is pressed, onb is pulled low and the regulator turns on. the switch must be pressed long enough for the microcontroller ( c) to exit reset (200ms) and drive ona high. a small capacitor is added to help debounce the switch. the c issues a logic high to ona, which holds the part on regardless of the switch state. to turn the regulator off, press the switch again, allowing the c to read the switch status and pull ona low. when the switch is released, onb is pulled high. ___________________ chip infor mation transistor count: 1649 substrate connected to gnd max1705 2 nicd/nimh 2.4 3.3 730 2 nicd/nimh 2.4 5.0 500 3 nicd/nimh or 1 li-ion 3.6 5.0 850 max1706 450 350 550 table 5. typical available output current m c v dd i/o max1705 max1706 ona onb out i/o 0.1 m f on/off 270k 270k figure 10. momentary pushbutton on/off switch max1705 max1706 p a rf lx pout gnd ldo control inputs m c i/o figure 9. typical phone application 1 nicd/nimh 1.2 3.3 300 200 number of cells input voltage (v) step-up output voltage: (pa power supply) (v) total output current (ma)
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 18 ______________________________________________________________________________________ 4.0 ?.1 0.30 ?.05 0.8 ?.05 0.30r max. b o k o 2.2 ?.1 0.5 radius typical a0 4.0 ?.1 2.0 ?.05 1.5 +0.1/-0.0 diameter 1.75 ?.1 1.0 ?.1 a 8.0 ?.3 3.5 ?.05 1.0 minimum a ao = 3.1mm ?.1 bo = 2.7mm ?.1 ko = 1.2mm ?.1 note: dimensions are in mm. and follow eia481-1 standard. __________________________________________________ t ape-and-reel infor mation
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator ______________________________________________________________________________________ 19 ________________________________________________________ package infor mation qsop.eps
max1705/max1706 1- to 3-cell, high-cur r ent, low-noise, step-up dc-dc conver ters with linear regulator 20 ______________________________________________________________________________________ notes

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