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for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim's website at www.maxim-ic.com. general description the MAX8625A pwm step-up/down regulator is intend- ed to power digital logic, hard disk drives, motors, and other loads in portable, battery-powered devices such as pdas, cell phones, digital still cameras (dscs), and mp3 players. the MAX8625A provides either a fixed 3.3v or adjustable output voltage (1.25v to 4v) at up to 0.8a from a 2.5v to 5.5v input. the MAX8625A utilizes a 2a peak current limit. maxim? proprietary h-bridge topology* provides a seamless transition through all operating modes without the glitches commonly seen with other devices. four internal mosfets (two switches and two synchronous rectifiers) with internal compensation minimize external components. a skip input selects a low-noise, fixed- frequency pwm mode, or a high-efficiency skip mode where the converter automatically switches to pfm mode under light loads for best light-load efficiency. the internal oscillator operates at 1mhz to allow for a small external inductor and capacitors. the MAX8625A features current-limit circuitry that shuts down the ic in the event of an output overload. in addi- tion, soft-start circuitry reduces inrush current during startup. the ic also features true shutdown tm , which disconnects the output from the input when the ic is disabled. the MAX8625A is available in a 3mm x 3mm, 14-pin tdfn package. applications pdas and smartphones dscs and camcorders mp3 players and cellular phones battery-powered hard disk drive (hdd) features ? four internal mosfet true h-bridge buck/boost ? glitch-free, buck-boost transitions ? minimal output ripple variation on transitions ? up to 92% efficiency ? 37 a (typ) quiescent current in skip mode ? 2.5v to 5.5v input range ? fixed 3.3v or adjustable output ? 1 a (max) logic-controlled shutdown ? true shutdown ? output overload protection ? internal compensation ? internal soft-start ? 1mhz switching frequency ? thermal-overload protection ? small 3mm x 3mm, 14-pin tdfn package MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter ________________________________________________________________ maxim integrated products 1 ordering information MAX8625A skip in gnd fb out lx1 lx2 on input 2.7v to 5.5v output 3.3v off on pwm skip ref typical operating circuit 19-1006; rev 2; 10/08 * us patent #7,289,119. true shutdown is a trademark of maxim integrated products, inc. evaluation kit available note: the device is specified over the -40? to +85? extended temperature range. + denotes a lead-free package. ** ep = exposed pad. part pin- package top mark MAX8625Aetd+ 14 tdfn-ep** (3mm x 3mm) abq MAX8625A tdfn-ep top view 245 13 11 10 in gnd out lx1 lx2 on 1 + 14 in lx1 3 12 gnd lx2 6 9 out skip 7 8 ref fb ep ep = exposed pad. pin configuration
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = 3.6v, on = skip = in, fb = gnd, v out = 3.3v, lx_ unconnected, c ref = c5 = 0.1? to gnd, figure 4. t a = -40? to +85?. typical values are at t a = +25?, unless otherwise noted.) (note 2) 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. in, out, skip , on to gnd ......................................-0.3v to +6v ref, fb, to gnd...............................................-0.3v, (in + 0.3v) lx2, lx1 (note 1).........................................................?.5a rms continuous power dissipation (t a = +70?) single-layer board (derate 18.5mw/? above t a = +70?) ...................................................1482mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units supply range v in 2.5 5.5 v uvlo threshold uvlo v in rising, 60mv hysteresis 2.20 2.49 v quiescent supply current, fpwm mode, switching i in no load, v out = 3.2v 15 22 ma quiescent supply current, skip mode, switching i in skip = gnd, no load 37 ? quiescent supply current, no switching, skip mode i in skip = gnd, fb = 1.3v 35 45 ? on = gnd, t a = +25? 0.1 1 shutdown supply current i in t a = +85? 0.2 ? pwm mode, v in = 2.5v to 5.5v 3.30 v i out = 0 to 0.5a, v in = 2.5v to 5.5v, t a = -40? to +85? (note 3) -1 +1 % skip mode, valley regulation value 3.28 v average skip voltage 3.285 output voltage accuracy (fixed output) load step +0.5a -3 % output voltage range (adjustable output) 1.25 4.00 v maximum output current v in = 3.6v 0.80 a soft-start l = 3.3?; c out = c3 + c4 = 44? 250 ma/ms load regulation i out = 0 to 500ma 0.1 %/a line regulation v in = 2.5v to 5.5v 0.03 %/v out bias current i out v out = 3.3v 3 a ref output voltage v ref v in = 2.5v to 5.5v 1.244 1.25 1.256 v ref load regulation i ref = 10? 1 mv fb feedback threshold v fb i out = 0 to full load, pwm mode; v in = 2.5v to 5.5v 1.244 1.25 1.258 v note 1: lx1 and lx2 have internal clamp diodes to in, pgnd and out, pgnd, respectively. applications that forward bias these diodes should take care not to exceed the device's power-dissipation limits.
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter _______________________________________________________________________________________ 3 note 2: devices are production tested at t a = +25?. specifications over the operating temperature range are guaranteed by design and characterization. note 3: limits are guaranteed by design and not production tested. note 4: the idle-mode current threshold is the transition point between fixed-frequency pwm operation and idle-mode operation. the specification is given in terms of output load current for an inductor value of 3.3?. for the step-up mode, the idle-mode transition varies with input to the output-voltage ratios. electrical characteristics (continued) (v in = 3.6v, on = skip = in, fb = gnd, v out = 3.3v, lx_ unconnected, c ref = c5 = 0.1? to gnd, figure 4. t a = -40? to +85?. typical values are at t a = +25?, unless otherwise noted.) (note 2) parameter symbol conditions min typ max units fb dual-mode threshold v fbdm 75 100 125 mv v fb = 1.3v, t a = +25? 0.001 0.1 fb leakage current i fb v fb = 1.3v, t a = +85? 0.01 ? on, skip input high voltage v ih 2.5v < v in < 5.5v 1.6 v on, skip input low voltage v il 2.5v < v in < 5.5v 0.45 v 2.5v < v in < 5.5v, t a = +25? 0.001 1 on input leakage current i ihl t a = +85? 0.01 ? i skiph v skip = 3.6v 3 12 skip input leakage current i skipl v skip = 0v -2 -0.2 ? peak current limit i limp lx1 pmos 1700 2000 2300 ma fault latch-off delay 100 ms each mosfet, t a = +25? 0.05 0.1 mosfet on-resistance r on each mosfet, v in = 2.5v to 5.5v, t a = -40? to +85? 0.2 rectifier-off current threshold i lx1off skip = gnd 125 ma skip = gnd, load decreasing 100 idle-mode current threshold (note 4) i skip load increasing 300 ma v in = v out = 5.5v, v lx1 = 0v to v in , v lx2 = 0v to v out , t a = +25? 0.01 1 lx1, lx2 leakage current i lxlkg t a = +85? 0.2 ? v in = v lx1 = v lx2 = 0v, v out = 5.5v, measure i (lx2), t a = +25? 0.01 1 out reverse current i lxlkgr t a = +85? 0.5 ? minimum t on t onmin 25 % osc frequency f oscpwm 850 1000 1150 khz thermal shutdown 15? hysteresis +165 ?
typical operating characteristics (v in = 3.6v, skip = gnd, t a = +25?, figure 4, unless otherwise noted.) MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter 4 _______________________________________________________________________________________ efficiency vs. load current skip and fpwm modes MAX8625A toc01 load current (ma) efficiency (%) 100 10 1 10 20 30 40 50 60 70 80 90 100 0 0.1 1000 v out = 3.3v v in = 2.7v 3.0v, 3.3v, 3.6v, 4.2v, 5.0v 60 70 65 80 75 85 90 95 100 2.0 3.0 3.5 2.5 4.0 4.5 5.0 5.5 6.0 skip-mode efficiency vs. input voltage MAX8625A toc02 input voltage (v) efficiency (%) 100ma 300ma 500ma v out = 3.3v load current = 100ma, 300ma, 500ma efficiency vs. load current fpwm mode (figure 3) MAX8625A toc03 load current (ma) efficiency (%) 100 10 1 10 20 30 40 50 60 70 80 90 100 0 0.1 1000 v out = 2.8v v in = 2.7v 3.0v, 3.3v, 3.6v, 4.2v, 5.0v efficiency vs. load current fpwm mode (figure 3) MAX8625A toc04 load current (ma) efficiency (%) 100 10 1 10 20 30 40 50 60 70 80 90 100 0 0.1 1000 v out = 3.45v v in = 2.7v 3.0v, 3.3v, 3.6v, 4.2v, 5.0v output voltage (3.3v internal fb) vs. load current MAX8625A toc05 load current (ma) deviation (%) 100 10 1 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 -2.0 0.1 1000 v out = 3.3v t a = +25 c, t a = -40 c, t a = +85 c, output voltage (2.8v external fb) vs. load current (figure 3) MAX8625A toc06 load current (ma) deviation (%) 100 10 1 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 -2.0 0.1 1000 v out = 2.8v t a = +25 c, t a = -40 c, t a = +85 c 3.27 3.29 3.28 3.31 3.30 3.32 3.33 3.0 4.0 4.5 3.5 5.0 5.5 6.0 output voltage vs. input voltage with internal fb resistors MAX8625A toc07 input voltage (v) output voltage (v) load: 500ma, v out = 3.3v t a = +25 c, t a = -40 c, t a = +85 c 2.75 2.77 2.76 2.79 2.78 2.81 2.80 2.82 3.0 4.0 4.5 3.5 5.0 5.5 6.0 output voltage vs. input voltage with external fb resistors MAX8625A toc08 input voltage (v) output voltage (v) load: 500ma, v out = 2.8v t a = +25 c, t a = -40 c, t a = +85 c (figure 3) supply current vs. input voltage with no load MAX8625A toc09 input voltage (v) supply current (ma) 5.5 5.0 4.5 4.0 3.5 3.0 2.5 0.1 1 10 100 0.01 2.0 6.0 no load v out = 3.3v fpwm mode
typical operating characteristics (continued) (v in = 3.6v, skip = gnd, t a = +25?, figure 4, unless otherwise noted.) MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter _______________________________________________________________________________________ 5 0 200 100 400 300 600 500 700 900 800 1000 2.0 3.0 3.5 2.5 4.0 4.5 5.0 5.5 6.0 maximum load current vs. input voltage MAX8625A toc10 input voltage (v) maximum load current (ma) v out = 3.3v 1 s/div switching waveforms v in = 3v, load = 500ma, v out = 3.3v MAX8625A toc11 v lx1 2v/div v out 50mv/div (ac-coupled) v lx2 2v/div i lx 500ma/div 1 s/div switching waveforms v in = 3.3v, load = 500ma, v out = 3.3v MAX8625A toc12 v lx1 2v/div v out 50mv/div (ac-coupled) v lx2 2v/div i lx 500ma/div 1 s/div switching waveforms v in = 3.6v, load = 500ma, v out = 3.3v MAX8625A toc13 v lx1 2v/div v out 50mv/div (ac-coupled) v lx2 2v/div i lx 500ma/div 10 s/div skip mode v in = 3v, load = 20ma, v out = 3.288v MAX8625A toc14 ch1 = v lx1 2v/div v out 20mv/div (ac-coupled) ch2 = v lx2 2v/div i lx 500ma/div 1 s/div fpwm mode v in = 3v, load = 20ma, v out = 3.308v MAX8625A toc15 v lx1 2v/div out 20mv/div (ac-coupled) v lx2 2v/div i lx 500ma/div
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter 6 _______________________________________________________________________________________ 2ms/div startup waveforms v in = 3.6v, load = 5 , v out = 3.288v MAX8625A toc16 shdn 2v/div v out 20mv/div i batt 500ma/div i lx 500ma/div 2ms/div startup waveforms (figure 3) v in = 3.6v, load = 30 , v out = 1.5v MAX8625A toc17 shdn 2v/div i batt 100ma/div v out 500ma/div i lx 500ma/div 400 s/div load transient v out = 3.3v MAX8625A toc18 v out 100mv/div (dc offset = 3.3v) i lx 500ma/div i batt 250ma/div typical operating characteristics (continued) (v in = 3.6v, skip = gnd, t a = +25?, figure 4, unless otherwise noted.) 1ms/div line transient v out = 3.3v, load = 5.5 , v in ramp 3v to 4v MAX8625A toc19 ch1 = v in 500mv/div 3v offset ch2 = v out 50mv/div (ac-coupled) bode plot gain and phase vs. frequency MAX8625A toc20 frequency (khz) gain (db) 100 10 -50 -40 -30 -20 -10 0 10 20 30 40 -60 1 1000 v in = 3.6 v out = 3.3v load = 200ma -180 -144 -108 -72 -36 0 36 72 108 144 180 phase (deg) gain phase 0.90 0.94 0.92 0.98 0.96 1.04 1.02 1.00 1.06 -40 0 -20 20 40 60 80 100 oscillator frequency vs. temperature MAX8625A toc21 temperature ( c) oscillator frequency (mhz)
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter _______________________________________________________________________________________ 7 typical operating characteristics (continued) (v in = 3.6v, skip = gnd, t a = +25?, figure 4, unless otherwise noted.) 2.28 2.34 2.32 2.30 2.36 2.38 2.40 2.42 2.44 2.46 2.48 -50 0 -25 25 50 75 100 minimum startup voltage vs. temperature MAX8625A toc22 temperature ( c) minimum startup voltage (v) v out = 3.3v, no load 1.22 1.24 1.23 1.26 1.25 1.27 1.28 -40 20 40 -20 0 60 80 100 reference vs. temperature no load MAX8625A toc23 temperature ( c) reference (v) v out = 3.3v v in = 3.0v, 3.6v, 4.2v, 5.0v 1.22 1.24 1.23 1.26 1.25 1.27 1.28 -40 20 40 -20 0 60 80 100 reference vs. temperature with 300ma load MAX8625A toc24 temperature ( c) reference (v) v out = 3.3v v in = 3.0v, 3.6v, 4.2v, 5.0v 100 s/div shutdown due to overload v in = 3.6v, v out = 3.288v MAX8625A toc25 v lx2 2v/div v lx2 2v/div v out 500mv/div i lx 500ma/div 2 s/div boost-to-buck transition fpwm mode v in = 3.6v, v out = 3.288v MAX8625A toc26 v in 1v/div dc offset = 3v v out 100mv/div ac-coupled i lx 200ma/div
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter 8 _______________________________________________________________________________________ detailed description the MAX8625A step-up/down architecture employs a true h-bridge topology that combines a boost converter and a buck converter topology using a single inductor and output capacitor (figure 1). the MAX8625A utilizes a pulse-width modulated (pwm), current-mode control scheme and operates at a 1mhz fixed frequency to minimize external component size. a proprietary h-bridge design eliminates mode changes when transi- tioning from buck to boost operation. this control scheme provides very low output ripple using a much smaller inductor than a conventional h-bridge, while avoiding glitches that are commonly seen during mode transitions with competing devices. the MAX8625A switches at an internally set frequency of 1mhz, allowing for tiny external components. internal compensation further reduces the external component count in cost- and space-sensitive applications. the MAX8625A is optimized for use in hdds, dscs, and other devices requiring low-quiescent current for opti- mal light-load efficiency and maximum battery life. control scheme the MAX8625A basic noninverting step-up/down con- verter operates with four internal switches. the control logic determines which two internal mosfets operate to maintain the regulated output voltage. unlike a tradi- tional h-bridge, the MAX8625A utilizes smaller peak- inductor currents, thus improving efficiency and lowering input/output ripple. the MAX8625A uses three operating phases during each switching cycle. in phase 1 (fast-charge), the inductor current ramps up with a di/dt of v in /l. in phase 2 (slow charge/discharge), the current either ramps up or down depending on the difference between the input voltage and the output voltage (v in - v out )/l. in phase 3 (discharge), the inductor current discharges at a rate of v out /l through mosfets p2 and n1 (see figure 1). an additional fourth phase (phase 4: hold) is entered when the inductor current falls to zero during phase 3. this fourth phase is only used during skip operation. the state machine (figure 2) decides which phase to use and when to switch phases. the converter goes through the first three phases in the same order at all pin description pin name function 1, 2 lx1 inductor connection 1. connect the inductor between lx1 and lx2. both lx1 pins must be connected together externally. lx1 is internally connected to gnd during shutdown. 3, 4 lx2 inductor connection 2. connect the inductor between lx1 and lx2. both lx2 pins must be connected together externally. lx2 is internally connected to gnd during shutdown. 5 on enable input. connect on to the input or drive high to enable the ic. drive on low to disable the ic. 6 skip mode select input. connect skip to gnd to enable skip mode. this mode provides the best overall efficiency curve. connect skip to in to enable forced-pwm mode. this mode provides the lowest noise, but reduces light- load efficiency compared to skip mode. 7fb feedback input. connect to ground to set the fixed 3.3v output. connect fb to the center tap of an external resistor-divider from the output to gnd to set the output voltage to a different value. v fb regulates to 1.25v. 8 ref reference output. bypass ref to gnd with a 0.1? ceramic capacitor. v ref is 1.25v and is internally pulled to gnd during shutdown. 9, 10 out power output. bypass out to gnd with two 22? ceramic capacitors. both out pins must be connected together externally. 11, 12 gnd ground. connect the exposed pad and gnd directly under the ic. 13, 14 in power-supply input. bypass in to gnd with two 22? ceramic capacitors. connect in to a 2.5v to 5.5v supply. both in pins must be connected together externally. ?p exposed pad. connect to gnd directly under the ic. connect to a large ground plane for increased thermal performance.
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter _______________________________________________________________________________________ 9 times. this reduces the ripple and removes any mode transitions from boost-only or buck-only to hybrid modes as seen in competing h-bridge converters. the time spent in each phase is set by a pwm con- troller, using timers and/or peak-current regulation on a cycle-by-cycle basis. the heart of the pwm control block is a comparator that compares the output volt- age-error feedback signal and the sum of the current- sense and slope compensation signals. the current- mode control logic regulates the inductor current as a function of the output error voltage signal. the current- sense signal is monitored across the mosfets (p1, n1, and n2). a fixed time delay of approximately 30ns occurs between turning the p1 and n2 mosfets off, and turning the n1 and p2 mosfets on. this dead time prevents efficiency loss by preventing ?hoot- through?current. step-down operation (v in > v out ) during medium and heavy loads and v in > v out , mosfets p1 and n2 turn on to begin phase 1 at the clock edge and ramp up the inductor current. the duration of phase 1 is set by an internal timer. during phase 2, n2 turns off, and p2 turns on to further ramp up inductor current and also transfer charge to the out- put. this slow charge phase is terminated on a clock edge and p1 is turned off. the converter now enters the fast discharge phase (phase 3). in phase 3, n1 turns on and the inductor current ramps down to the valley current-regulation point set by the error signal. at the end of phase 3, both p2 and n1 turn off and another phase 1 is initiated and the cycle repeats. with skip asserted low, during light loads when induc- tor current falls to zero in phase 3, the converter switch- es to phase 4 to reduce power consumption and avoid figure 1. simplified block diagram max8625 gm fb uvlo p1 current sense reference pwm/pfm control p1 p2 n2 out in ref lx1 lx2 n1 on skip oscillator gnd 1.25v 125mv
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter 10 ______________________________________________________________________________________ shuttling current in and out of the output capacitor. if skip is asserted high for forced-pwm mode, phase 4 is not entered and current shuttling is allowed (and is necessary to maintain the pwm operation frequency when no load is present). step-up operation (v in < v out ) during medium and heavy loads when v in < v out, mosfets p1 and n2 turn on at the clock edge to ramp up the inductor current. phase 1 terminates when the inductor current reaches the peak target current set by the pwm comparator and n2 turns off. this is followed by a slow-discharge phase (phase 2) instead of a charge phase (since v in is less than v out ) when p2 turns on. the slow-discharge phase terminates on a clock edge. the converter now enters the fast-dis- charge phase (phase 3). during phase 3, p1 turns off and n1 turns on. at the end of the minimum time, both p2 and n1 turn off and the cycle repeats. if skip is asserted low, during light loads when inductor current falls to zero in phase 3, the converter switches to phase 4 (hold) to reduce power consumption and avoid shuttling current in and out of the output. if skip is high to assert forced-pwm mode, the converter never enters phase 4 and allows negative inductor current. step-up/down transition-zone operation (v in = v out ) when v in = v out , the converter still goes through the three phases for moderate to heavy loads. however, the maximum time is now spent in phase 2 where inductor current di/dt is almost zero, since it is propor- tional to (v in - v out ). this eliminates transition glitches figure 2. state diagram fault timeout (asynchronous from anywhere) error on = 1 p1, p2 = off n1, n2 = on off on = 0 p1, p2 = off n1, n2 = on i q = 0 a on = 0 (asynchronous from anywhere) refok = 0 or uvlo = 0 (asynchronous from anywhere) phase 2 slow charge/ discharge osc = on p1, p2 = on n1, n2 = off phase 3 fast discharge osc = on p2, n1 = on p1, n2 = off phase 1 fast-charge osc = on p1, n2 = on p2, n1 = off phase 4 hold osc = off n1, n2 = on p1, p2 = off power-up on = 1, p1, p2 = off, n1, n2 = on, osc = on and ref = on if uvlo ok t2-3 t3-4 t1-2 t3-1 t1-3 t4-1 trun tpup (skip)
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter ______________________________________________________________________________________ 11 or oscillation between the boost and buck modes as seen in other step-up/down converters. see the switch- ing waveforms for each of the three modes and transi- tion waveforms in the typical operating characteristics section. forced-pwm mode drive skip high to operate the MAX8625A in forced- pwm mode. in this mode, the ic operates at a constant 1mhz switching frequency with no pulse skipping. this scheme is desirable in noise-sensitive applications because the output ripple is minimized and has a pre- dictable noise spectrum. forced pwm consumes higher supply current at light loads due to constant switching. skip mode drive skip low to operate the MAX8625A in skip mode to improve light-load efficiency. in skip mode, the ic switches only as necessary to maintain the output at light loads, but still operates with fixed-frequency pwm at medium and heavy loads. this maximizes light-load efficiency and reduces the input quiescent current to 37? (typ). do not dynamically transition between skip and fpwm. the MAX8625A is not designed for dynamic transitions between fpwm and skip modes. spikes of negative inductor current are possible when making these types of dynamic transitions. the magnitude of the spike depends on the load and output capacitance. the MAX8625A has no protection against these types of negative current spikes. load regulation and transient response during a load transient, the output voltage instantly changes due to the esr of the output capacitors by an amount equal to their esr times the change in load current ( v out = r esr x i load ). the output voltage then deviates further based on the speed at which the loop compensates for the load step. increasing the out- put capacitance reduces the output-voltage droop. see the capacitor selection section. the typical application circuit limits the output transient droop to less than 3%. see the typical operating characteristics section. soft-start soft-start prevents input inrush current during startup. internal soft-start circuitry ramps the peak inductor cur- rent with an internal dac in 8ms. once the output reaches regulation, the current limit immediately jumps to the maximum threshold. this allows full load capabil- ity as soon as regulation is reached, even if it occurs before the 8ms soft-start time is complete. when using the MAX8625A at low input voltages (close to uvlo and < 3v), it is recommended that the on pin should not be tied to the batt or supply voltage node directly. the on pin should be held low for > 1ms after power to the MAX8625A is applied before it is driven high for normal operation. shutdown drive on low to place the MAX8625A in shutdown mode and reduce supply current to less than 1?. during shutdown, out is disconnected from in, and lx1 and lx2 are connected to gnd. drive on high for normal operation. fault and thermal shutdown the MAX8625A contains current-limit and thermal shut- down circuitry to protect the ic from fault conditions. when the inductor current exceeds the current limit (2a for the MAX8625A), the converter immediately enters phase 3 and an internal 100ms timer starts. the con- verter continues to commutate through the three phas- es, spending most of its time in phase 1 and phase 3. if the overcurrent event continues and the output is out of regulation for the duration of the 100ms timer, the ic enters shutdown mode and the output latches off. on must then be toggled to clear the fault. if the overload is removed before the 100ms timer expires, the timer is cleared and the converter resumes normal operation. the thermal-shutdown circuitry disables the ic switching if the die temperature exceeds +165?. the ic begins soft-start once the die temperature cools by 15?.
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter 12 ______________________________________________________________________________________ applications information selecting the output voltage the MAX8625A output is nominally fixed at 3.3v. connect fb to gnd to select the internally fixed-output voltage. for an adjustable output voltage, connect fb to the center tap of an external resistor-divider connect- ed from the output to gnd (r1 and r2 in figure 3). select 100k for r2 and calculate r1 using the follow- ing equation: where v fb = 1.25v and v out is the desired output reg- ulation voltage. v out must be between 1.25v and 4v. note that the minimum output voltage is limited by the minimum duty cycle. v out cannot be below 1.25v. calculating maximum output current the maximum output current provided by the MAX8625A circuit depends on the inductor value, switching frequen- cy, efficiency, and input/output voltage. see the typical operating characteristics section for the maximum load current vs. input voltage graph. capacitor selection the input and output ripple currents are both discontin- uous in this topology. therefore, select at least two 22? ceramic capacitors at the input. select two 22? ceramic output capacitors. for best stability over a wide temperature range, use x5r or better dielectric. inductor selection the recommended inductance range for the MAX8625A is 3.3? to 4.7?. larger values of l give a smaller ripple, while smaller l values provide a better transient response. this is because, for boost and step- up/down topologies, the crossover frequency is inversely proportional to the value of l for a given load and input voltage. the MAX8625A is internally compen- sated, and therefore, the choice of power components for stable operation is bounded. a 3.3? inductor with 2a rating is recommended for the 3.3v fixed output with 0.8a load. pcb layout and routing good pcb layout is important to achieve optimal per- formance from the MAX8625A. poor design can cause excessive conducted and/or radiated noise. conductors carrying discontinuous currents and any high-current path should be made as short and wide as possible. keep the feedback network (r1 and r2) very close to the ic, preferably within 0.2 inches of the fb and gnd pins. nodes with high dv/dt (switching nodes) should be kept as small as possible and routed away from fb. connect the input and output capacitors as close as possible to the ic. refer to the MAX8625A evaluation kit for a pcb layout example. rk v v out fb 1 100 1 = ? ? ? ? ? ? ? figure 3. typical application circuit (adjustable output) u1 MAX8625A r2 100k r1 140k in skip in out fb out lx1 lx1 lx2 lx2 12 13 14 6 on 5 ref 8 34 l 3.3 h c1, c2 22 f c5 0.1 f 9 7 10 c3, c4 22 f input 2.7v to 5.5v mode selection input output 3v off on gnd gnd 11 12
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter ______________________________________________________________________________________ 13 chip information process: bicmos figure 4. typical application circuit (fixed 3.3v output) u1 MAX8625A in skip in out fb out lx1 lx1 lx2 lx2 12 13 14 6 on 5 ref 8 34 l 3.3 h c1, c2 22 f c5 0.1 f 9 7 10 c3, c4 22 f input 2.7v to 5.5v mode selection input output 3.3v off on gnd gnd 11 12
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter 14 ______________________________________________________________________________________ package type package code document no. 14 tdfn-ep t1433-2 21-0137 package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . 6, 8, &10l, dfn thin.eps
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter ______________________________________________________________________________________ 15 common dimensions symbol min. max. a 0.70 0.80 d 2.90 3.10 e 2.90 3.10 a1 0.00 0.05 l 0.20 0.40 pkg. code n d2 e2 e jedec spec b [(n/2)-1] x e package variations 0.25 min. k a2 0.20 ref. 2.00 ref 0.250.05 0.50 bsc 2.300.10 10 t1033-1 2.40 ref 0.200.05 - - - - 0.40 bsc 1.700.10 2.300.10 14 t1433-1 1.500.10 mo229 / weed-3 0.40 bsc - - - - 0.200.05 2.40 ref t1433-2 14 2.300.10 1.700.10 t633-2 6 1.500.10 2.300.10 0.95 bsc mo229 / weea 0.400.05 1.90 ref t833-2 8 1.500.10 2.300.10 0.65 bsc mo229 / weec 0.300.05 1.95 ref t833-3 8 1.500.10 2.300.10 0.65 bsc mo229 / weec 0.300.05 1.95 ref 2.300.10 mo229 / weed-3 2.00 ref 0.250.05 0.50 bsc 1.500.10 10 t1033-2 package information (continued) for the latest package outline information and land patterns, go to www.maxim-ic.com/packages .
MAX8625A high-efficiency, seamless transition, step-up/down dc-dc converter maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 16 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2008 maxim integrated products printed usa is a registered trademark of maxim integrated products. inc. revision history revision number revision date description pages changed 0 3/08 initial release 1 5/08 added pcb layout and routing section 12 2 10/08 updated skip mode and soft-start sections 2, 11

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