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general description the aat2550 is a fully integrated total power solu- tion with two step-down converters plus a single- cell lithium-ion / polymer battery charger. the step- down converter input voltage range spans 2.7v to 5.5v, making the aat2550 ideal for systems pow- ered by single-cell lithium-ion/polymer batteries. the battery charger is a complete constant current/ constant voltage linear charger. it offers an inte- grated pass device, reverse blocking protection, high current accuracy and voltage regulation, charge status, and charge termination. the charg- ing current is programmable via external resistor from 100ma to 1a. in addition to these standard features, the device offers over-voltage, over-cur- rent, and thermal protection. the two step-down converters are highly integrated, operating at a switching frequency of 1.4mhz, mini- mizing the size of external components while keep- ing switching losses low. each converter has inde- pendent input, enable, and feedback pins. the out- put voltage ranges from 0.6v to v in . each converter is capable of delivering up to 600ma of load current. the aat2550 is available in a pb-free, space-sav- ing, thermally-enhanced qfn44-24 package and is rated over the -40c to +85c temperature range. features ? two step-down converters: ? 600ma output current per converter ?v in range: 2.7v to 5.5v ? 1.4mhz switching frequency ? low r ds(on) 0.4 integrated power switches ? internal soft start ? 27a quiescent current per converter ? highly integrated battery charger: ? programmable charging current from 100ma to 1a ? pass device ? reverse blocking diodes ? current sensing resistor ? digital thermal regulation ? short-circuit, over-temperature, and current limit protection ? qfn44-24 package ? -40c to +85c temperature range applications ? cellular telephones ? digital cameras ? handheld instruments ? mp3, portable music, and portable media players ? pdas and handheld computers aat2550 total power solution for portable applications typical application 2550.2006.07.1.0 1 systempower ? aat2550 adapter serial interface stat1 stat2 adpset data enbat ina inb li-ion battery or adapter bat ts ct batt+ batt- temp battery pack lxa c outa fba v outa r set lxb c outb fbb v outb ena enb gnd adp
pin descriptions pin # symbol function 1 ena enable pin for converter a. when connected to logic low, it disables the step-down converter and consumes less than 1a of current. when connected to logic high, the converter operates normally. 2 lxa power switching node for converter a. connect the inductor to this pin. internally, it is connect- ed to the drain of both high- and low-side mosfets. 3, 17 pgnd power ground. connect the pgnd pins together as close to the ic as possible. connect agnd to pgnd at a single point as close to the ic as possible. 4 data status report to the microcontroller via serial interface (open drain). 5, 7 n/c not connected. 6 adpset charge current set point. connect a resistor from this pin to ground. refer to typical characteristics curves for resistor selection. 8 bat battery charging and sensing. connect the positive terminal of the battery to bat. 9 adp input for adapter charger. 10, 11, 22 agnd analog signal ground. connect agnd to pgnd at a single point as close to the ic as possible. 12 enbat enable pin for the battery charger. when connected to logic low, the battery charger is dis- abled and consumes less than 1a of current. when connected to logic high, the charger operates normally. 13 ts temperature sense input. connect to a 10k ntc thermistor. 14 stat2 battery charge status indicator pin to drive an led. it is an open drain input. 15 stat1 battery charge status indicator pin to drive an led. it is an open drain input. 16 ct timing capacitor to adjust internal watchdog timer. sets maximum charge time for adapter powered trickle, constant current, and constant voltage charge modes. 18 lxb power switching node for converter b. connect the inductor to this pin. internally, it is connect- ed to the drain of both high- and low-side mosfets. 19 enb enable pin for converter b. when connected to logic low, it disables the step-down converter and consumes less than 1a of current. when connected to logic high, the converter operates normally. 20 inb input voltage for converter b. 21 fbb output voltage feedback input for converter b. fbb senses the output voltage for regulation control. for fixed output versions, connect fbb to the output voltage. for adjustable versions, drive fbb from the output voltage through a resistive voltage divider. the fbb regulation threshold is 0.6v. 23 fba output voltage feedback input for converter a. fba senses the output voltage for regulation control. for fixed output versions, connect fba to the output voltage. for adjustable versions, drive fba from the output voltage through a resistive voltage divider. the fba regulation threshold is 0.6v. 24 ina input voltage for converter a. ep exposed paddle; connect to ground directly beneath the package. aat2550 total power solution for portable applications 2 2550.2006.07.1.0
pin configuration qfn44-24 (top view) absolute maximum ratings 1 thermal information symbol description value units p d maximum power dissipation 2.0 w ja thermal resistance 2 50 c/w symbol description value units v ina/b , v adp ina, inb, and adp voltages to gnd -0.3 to 6.0 v v lxa/b , v fba/b v lxa , v lxb , v fba , and v fbb to gnd -0.3 to v ina/b , v adp + 0.3 v v x voltage on all other pins to gnd -0.3 to 6.0 v t j operating junction temperature range -40 to 150 c t lead maximum soldering temperature (at leads, 10 sec) 300 c aat2550 total power solution for portable applications 2550.2006.07.1.0 3 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at co nditions other than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any one tim e. 2. mounted on an fr4 printed circuit board. 1 3 2 5 4 6 18 16 17 14 15 13 10 11 12 8 9 7 19 21 20 23 22 24 ena lxa pgnd data n/c a dpset n/c bat adp agnd agnd enba t stat1 ct stat2 ts pgnd lxb enb inb fbb a gnd fba ina
electrical characteristics 1 v in = 3.6v; t a = -40c to +85c, unless otherwise noted. typical values are at t a = 25c. symbol description conditions min typ max units step-down converters a and b v in input voltage 2.7 5.5 v v in rising 2.7 v v uvlo under-voltage lockout threshold hysteresis 100 mv v in falling 1.8 v v out output voltage tolerance i out = 0 to 600ma, -3.0 3.0 % v in = 2.7v to 5.5v v out output voltage range 0.6 v in v i out output current per converter 600 ma i q quiescent current each converter 27 70 a i shdn shutdown current v ena = v enb = gnd 1.0 a i lim p-channel current limit each converter 0.8 1.0 a i lx_leak lx leakage current v in = 5.5v, v lx = 0 to v in , 1.0 a v ena = v enb = gnd i fb_leak feedback leakage v fb = 0.6v 0.2 a r fb fb impedance v out > 0.6v 250 k v fb feedback threshold voltage accuracy no load, t a = 25c 0.591 0.6 0.609 v (0.6v adjustable version) r ds(on)h high-side switch on resistance 0.45 r ds(on)l low-side switch on resistance 0.40 v linereg line regulation v in = 2.7v to 5.5v 0.1 %/v f osc switching frequency 1.4 mhz t sd over-temperature shutdown threshold 140 c t hys over-temperature shutdown hysteresis 15 c v en(l) enable threshold low 0.6 v v en(h) enable threshold high 1.4 v aat2550 total power solution for portable applications 4 2550.2006.07.1.0 1. the aat2550 is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is assu red by design, characterization, and correlation with statistical process controls.
electrical characteristics 1 v adp = 5v; t a = -40c to +85c, unless otherwise noted. typical values are at t a = 25c. symbol description conditions min typ max units battery charger v adp adapter voltage range 4.0 5.5 v v uvlo under-voltage lockout rising edge 3.0 v uvlo hysteresis 150 mv i q quiescent current i charge = 100ma 0.75 3.0 ma i sleep sleep mode current v bat = 4.25v 0.3 1.0 a i leakage reverse leakage current v bat = 4v, adp pin open 1.0 a i shdn shutdown current v en = gnd 1.0 a v bat _ eoc 2 end of charge voltage accuracy 4.158 4.2 4.242 v v ch /v ch output charge voltage tolerance 0.5 % v min preconditioning voltage threshold 2.80 3.0 3.15 v v rch battery recharge voltage threshold v bat _ eoc - 0.1 v i ch charge current 100 1000 ma i ch /i ch charge current regulation tolerance 10 % v adpset adpset pin voltage constant current mode 2.0 v k ia current set factor: i ch /i adpset 4000 r ds(on) charger pass device v in = 5.5v 0.20 0.25 0.35 t c constant current mode time-out c t = 100nf, v adp = 5.5v 3.0 hour t p preconditioning time-out c t = 100nf, v adp = 5.5v 25 minute t v constant voltage mode time-out c t = 100nf, v adp = 5.5v 3.0 hour v s tat output low voltage i sink = 4ma 0.4 v i s tat stat sink current 8.0 ma v ovp over-voltage protection 4.4 v i tk /i ch pre-charge current 10 % i term /i ch charge termination threshold current 7.5 % i ts current source from ts pin 70 80 90 a ts 1 ts hot temperature fault threshold 310 330 350 mv hysteresis 15 ts 2 ts cold temperature fault threshold 2.2 2.3 2.4 v hysteresis 10 mv i d ata data pin sink current data pin is active low 3.0 ma v data(h) input high threshold 1.6 v v data(l) input low threshold 0.4 v s qpulse status request pulse width 200 ns t period system clock period 50 s f d ata data output frequency 20 khz t reg thermal loop regulation 90 c t loop _ in thermal loop entering threshold 110 c t loop _ out thermal loop exiting threshold 85 c t sd over-temperature shutdown threshold 145 c aat2550 total power solution for portable applications 2550.2006.07.1.0 5 1. the aat2550 is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is assu red by design, characterization, and correlation with statistical process controls. 2. end of charge voltage accuracy is specified over the 0 to 70c ambient temperature range.
typical characteristics?step-down converter aat2550 total power solution for portable applications 6 2550.2006.07.1.0 dc regulation (v out = 3.3v; l = 6.8h) output current (ma) output error (%) -1.0 -0.5 0.0 0.5 1.0 0.1 1 10 100 1000 v in = 5.0v v in = 4.2v v in = 3.6v efficiency vs. load (v out = 3.3v; l = 6.8 h) output current (ma) efficiency (%) 50 60 70 80 90 100 0.1 1 10 100 1000 v in = 3.6v v in = 4.2v v in = 5.0v dc regulation (v out = 2.5v) output current (ma) output error (%) -1.0 -0.5 0.0 0.5 1.0 0.1 1 10 100 1000 v in = 5.0v v in = 3.6v v in = 3.0v v in = 4.2v efficiency vs. load (v out = 2.5v; l = 6.8 h) output current (ma) efficiency (%) 50 60 70 80 90 100 0.1 1 10 100 1000 v in = 5.0v v in = 3.6v v in = 4.2v v in = 2.7v dc regulation (v out = 1.8v) output current (ma) output error (%) -1.0 -0.5 0.0 0.5 1.0 0.1 1 10 100 1000 v in = 4.2v v in = 3.6v v in = 2.7v efficiency vs. load (v out = 1.8v; l = 4.7 h) output current (ma) efficiency (%) 50 60 70 80 90 100 0.1 1 10 100 100 0 v in = 2.7v v in = 3.6v v in = 4.2v
typical characteristics?step-down converter aat2550 total power solution for portable applications 2550.2006.07.1.0 7 no load quiescent current vs. input voltage input voltage (v) supply current ( a) 10 15 20 25 30 35 40 45 50 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85 c 25 c -40 c frequency vs. input voltage input voltage (v) frequency variation (%) -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 v out = 1.8v v out = 2.5v v out = 3.3v switching frequency vs. temperature (v in = 3.6v; v out = 1.8v) temperature ( c) variation (%) -15.0 -12.0 -9.0 -6.0 -3.0 0.0 3.0 6.0 9.0 12.0 15.0 -40 -20 0 20 40 60 80 100 output voltage error vs. temperature (v in = 3.6v; v o = 1.8v; i out = 400ma) temperature ( c) output error (%) -2.0 -1.0 0.0 1.0 2.0 -40 -20 0 20 40 60 80 100 line regulation (v out = 1.8v) input voltage (v) accuracy (%) -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 i out = 10ma i out = 400ma i out = 1ma soft start (v in = 3.6v; v out = 1.8v; i out = 400ma) time (100 s/div) enable and output voltage (top) (v) inductor current (bottom) (a) -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 v en i l v o
typical characteristics?step-down converter aat2550 total power solution for portable applications 8 2550.2006.07.1.0 load transient response (1ma to 300ma; v in = 3.6v; v out = 1.8v; c 1 = 10 f; c ff = 100pf) output voltage (top) (v) load and inductor current (200ma/div) (bottom) time (50 1.7 1.8 1.9 2.0 v o 300ma 1ma 0 i o i l n-channel r ds(on) vs. input voltage input voltage (v) r ds(on)l (m ) 300 350 400 450 500 550 600 650 700 750 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 25 c 120 c 100 c 85 c p-channel r ds(on) vs. input voltage input voltage (v) r ds(on)h (m ) 300 350 400 450 500 550 600 650 700 750 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 25 c 120 c 100 c 85 c load transient response (300ma to 400ma; v in = 3.6v; v out = 1.8v; c 1 = 10 f; c 4 = 100pf) output voltage (top) (v) load and inductor current (200ma/div) (bottom) time (50 1.775 1.800 1.825 1.850 0.1 0.2 0.3 0.4 v o i o i l 400ma 300ma load transient response (300ma to 400ma; v in = 3.6v; v out = 1.8v; c 1 = 10 f) output voltage (top) (v) load and inductor current (200ma/div) (bottom) time (50 1.75 1.80 1.85 1.90 0.1 0.2 0.3 0.4 v o i o i l 400ma 300ma load transient response (300ma to 400ma; v in = 3.6v; v out = 1.8v; c 1 = 4.7 f) output voltage (top) (v) load and inductor current (200ma/div) (bottom) time (50 1.75 1.80 1.85 1.90 0.1 0.2 0.3 0.4 v o i o i l 400ma 300ma
typical characteristics?step-down converter aat2550 total power solution for portable applications 2550.2006.07.1.0 9 output ripple (v in = 3.6v; v out = 1.8v; i out = 400ma) time (500ns/div) output voltage (ac coupled) (top) (mv) inductor current (bottom) (a) -120 -100 -80 -60 -40 -20 0 20 40 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 v o i l output ripple (v in = 3.6v; v out = 1.8v; i out = 1ma) time (10s/div) output voltage (ac coupled) (top) (mv) inductor current (bottom) (a) -120 -100 -80 -60 -40 -20 0 20 40 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 v o i l line response (v out = 1.8v @ 400ma) output voltage (top) (v) input voltage (bottom) (v) time (25 s/div) 1.76 1.77 1.78 1.79 1.80 1.81 1.82 3.0 3.5 4.0 4.5 5.0 5.5 6.0
aat2550 total power solution for portable applications 10 2550.2006.07.1.0 typical characteristics?battery charger fast charge current vs. temperature (adpset = 8.06k ) temperature ( 900 920 940 960 980 1000 1020 1040 1060 1080 1100 -50 -25 0 25 50 75 100 preconditioning i ch vs. temperature (adpset = 8.06k ) temperature ( 80 90 100 110 120 -50 -25 0 25 50 75 100 preconditioning threshold voltage vs. temperature temperature ( c) v min (v) 2.95 2.96 2.97 2.98 2.99 3.00 3.01 3.02 3.03 3.04 3.05 -50 -25 0 25 50 75 100 end of charge voltage regulation vs. temperature temperature ( c) v bat (v) 4.158 4.179 4.200 4.221 4.242 -50 -25 0 25 50 75 100 battery voltage vs. supply voltage supply voltage (v) v bat (v) 4.158 4.179 4.200 4.221 4.242 4.5 4.75 5.0 5.25 5.5 i fastcharge vs. r set r set (k ) i fastcharge (ma) 10 100 1000 10000 1 10 100
typical characteristics?battery charger aat2550 total power solution for portable applications 2550.2006.07.1.0 11 counter timeout vs. temperature (ct = 0.1 f) temperature ( -10 -8 -6 -4 -2 0 2 4 6 8 10 -50 -25 0 25 50 75 100 adapter mode supply current vs. adpset resistor adpset resistor (k ) i q (ma) 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 1 10 100 1000 pre-conditioning constant current v il vs. supply voltage en pin (falling) supply voltage (v) v ih (v) 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 -40 c +25 c +85 c v ih vs. supply voltage en pin (rising) supply voltage (v) v ih (v) 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 -40 c +25 c +85 c fast charge current vs. supply voltage (adpset = 8.06k ) supply voltage (v) i ch (ma) 0 200 400 600 800 1000 1200 4.5 4.75 5.0 5.25 5.5 5.75 6.0 v bat = 3.3v v bat = 3.5v v bat = 3.9v charging current vs. battery voltage (adpset = 8.06k ; v in = 5.0v) battery voltage (v) i ch (a) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 2.5 2.9 3.3 3.7 4.1 4.5
typical characteristics?battery charger aat2550 total power solution for portable applications 12 2550.2006.07.1.0 temperature sense output current vs. temperature temperature ( c) ts pin current ( 72 74 76 78 80 82 84 86 88 -50 -25 0 25 50 75 10 0 ct pin capacitance vs. counter timeout time (hours) capacitance ( f) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0246810 precondition timeout precondition + constant current timeout or constant voltage timeout
aat2550 total power solution for portable applications 2550.2006.07.1.0 13 functional block diagram functional description the aat2550 is a highly integrated power manage- ment ic comprised of a battery charger and two step-down voltage converters. the battery charger is designed for charging single-cell lithium-ion / polymer batteries. featuring an integrated pass device and reverse blocking, it offers a constant current / constant voltage charge algorithm with a user-programmable charge current level. the two step-down converters have been designed to mini- mize external component size and maximize effi- ciency over the entire load range. each converter has independent enable and input voltage pins and can provide 600ma of load current. enb lxb err. amp. dh dl pgnd fbb voltage reference control logic logic ena lxa err. amp. dh dl pgnd fba voltage reference control logic logic inb charge control reverse blocking cv/pre- charge constant current current compare adp bat otp charge status stat2 stat1 4.2v enbat a dpset ts ina window comparator 80a watchdog timer ct uvlo
aat2550 total power solution for portable applications 14 2550.2006.07.1.0 battery charger the battery charger is designed to operate with standard ac adapter input sources, while requiring a minimum number of external components. it pre- cisely regulates charge voltage and current for sin- gle-cell lithium-ion / polymer batteries. the adapter charge input constant current level may be programmed up to 1a for rapid charging applications. the battery charger features thermal loop charge reduction. in the event of operating ambient temperatures exceeding the power dissi- pation abilities of the device package for a given constant current charge level, the charge control will enter into thermal regulation. when the system thermal regulation becomes active, the pro- grammed constant current charge amplitude will automatically decrease to a safe level for the pres- ent operating conditions. if the ambient tempera- ture drops to a level sufficient to allow the device to come out of thermal regulation, then the system will automatically resume charging at the full pro- grammed constant current level. this intelligent thermal management system permits the battery charger to operate and charge a battery cell safely over a wide range of ambient conditions, while maximizing the greatest possible charge current and minimizing the battery charge time for a given set of conditions. status monitor output pins are provided to indicate the battery charge state by directly driving two external leds. a serial interface output is also available to report any one of 12 distinct charge states to the host system microcontroller / micro- processor. battery temperature and charge state are fully monitored for fault conditions. in the event of an over-voltage or over-temperature condition, the device will automatically shut down, protecting the charging device, control system, and the bat- tery under charge. in addition to internal charge controller thermal protection, the charger also offers a temperature sense feedback function (ts pin) from the battery to shut down the device in the event the battery exceeds its own thermal limit dur- ing charging. all fault events are reported to the user either by simple status leds or via the data pin function. charging operation as shown in figure 1, there are four basic modes for the battery charge cycle: 1. pre-conditioning / trickle charge 2. constant current / fast charge 3. constant voltage 4. end of charge figure 1: typical charge profile. preconditioning (trickle charge) phase constant current phase constant voltage phase output charge voltage (v ch ) preconditioning voltage threshold (v min ) regulation current (i charge(reg) ) trickle charge and termination threshold
aat2550 total power solution for portable applications 2550.2006.07.1.0 15 battery preconditioning before the start of charging, the charger checks sev- eral conditions in order to assure a safe charging environment. the input supply must be above the minimum operating voltage, or under-voltage lock- out threshold (v uvlo ), for the charging sequence to begin. also, the battery temperature, as reported by a thermistor connected to the ts pin from the bat- tery, must be within the proper window for safe charging. when these conditions have been met and a battery is connected to the bat pin, the charg- er checks the state of the battery. if the battery volt- age is below the preconditioning voltage threshold (v min ), then the charge control begins precondition- ing the battery. the preconditioning trickle charge current is equal to the fast charge constant current divided by 10. for example, if the programmed fast charge current is 1a, then the preconditioning mode (trickle charge) current will be 100ma. battery pre- conditioning is a safety precaution for deeply dis- charged batteries and also helps to limit power dis- sipation in the pass transistor when the voltage across the device is at the greatest potential. fast charge/constant current charging battery preconditioning continues until the voltage on the bat pin exceeds the preconditioning voltage threshold (v min ). at this point, the charger begins the constant current fast charging phase. the fast charge constant current (i ch ) amplitude is programmed by the user via the r set resistor. the charger remains in the constant current charge mode until the battery reaches the voltage regulation threshold, v bat_eoc . constant voltage charging the system transitions to a constant voltage charging mode when the battery voltage reaches the output charge regulation threshold (v bat_eoc ) during the con- stant current fast charge phase. the regulation voltage level is factory programmed to 4.2v (1%). the charge current in the constant voltage mode drops as the bat- tery under charge reaches its maximum capacity. end of charge cycle termination and recharge sequence when the charge current drops to 7.5% of the pro- grammed fast charge current level in the constant voltage mode, the device terminates charging and goes into a sleep state. the charger will remain in a sleep state until the battery voltage decreases to a level below the battery recharge voltage threshold (v rch ). when the input supply is disconnected, the charger will automatically transition into a power- saving sleep mode. consuming only an ultra-low 0.3a in sleep mode, the charger minimizes battery drain when it is not charging. this feature is particu- larly useful in applications where the input supply level may fall below the battery charge or under-volt- age lockout level. in such cases where the input volt- age drops, the device will enter sleep mode and resume charging automatically once the input sup- ply has recovered from the fault condition. step-down converters the aat2550 offers two high-performance, 600ma, 1.4mhz step-down converters. both con- verters minimize external component size and opti- mize efficiency over the entire load range. the fixed output version requires only three external power components (c in , c out , and l) for each con- verter. the adjustable version is programmed with external feedback resistors to any voltage ranging from 0.6v to the input voltage. at dropout, the con- verter duty cycle increases to 100% and the output voltage tracks the input voltage minus the r ds(on) drop of the p-channel mosfet. input voltage range is 2.7v to 5.5v and each convert- er's efficiency has been optimized for all load condi- tions, ranging from no load to 600ma. the internal error amplifier and compensation provides excellent transient response, load regulation, and line regula- tion. soft start eliminates output voltage overshoot when the enable or the input voltage is applied. soft start / enable the internal soft start limits the inrush current dur- ing start-up. this prevents possible sagging of the input voltage and eliminates output voltage over- shoot. typical start-up time for a 4.7f output capacitor and load current of 600ma is 100s. the aat2550 offers independent enable pins for each converter. when connected to logic low, the enable input forces the respective step-down con- verter into a low-power, non-switching, shutdown state. the total input current during shutdown is less than 1a for each channel.
current limit and over-temperature protection for overload conditions, the peak input current is limited. to minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. thermal protection completely disables switching when internal dissipation becomes excessive. the junction over-temperature threshold is 140c with 15c of hysteresis. once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. under-voltage lockout the under-voltage lockout circuit prevents the device from improper operation at low input volt- ages. internal bias of all circuits is controlled via the vin input. under-voltage lockout (uvlo) guaran- tees sufficient v in bias and proper operation of all internal circuitry prior to activation. aat2550 total power solution for portable applications 16 2550.2006.07.1.0 system operation flow chart uvlo battery temp. monitor v ts1 v bat v min >v bat voltage phase test v p > v uvlo shut down mode shutdown mode no no yes yes low current conditioning charge low current conditioning charge battery temp. fault battery temp. fault no no current charging mode current charging mode yes voltage charging mode voltage charging mode i bat > i min no yes no switch on switch on yes yes charge completed charge completed recharge test v rch > v bat adp yes charge safety timer charge safety timer set expire power on reset power on reset sleep mode sleep mode power select output adpp output adpp no device temp. monitor t j > 110 c yes fault conditions monitor ov, ot yes thermal loop current reduction in adp charging mode thermal loop current reduction in adp charging mode no thermal loop enable thermal loop enable timing adp loop adp loop adp voltage test adp > v adpp no yes no enable
application information ac adapter power charging the adapter constant current charge levels can be programmed up to 1a. the aat2550 will operate from the adapter input over a 4.0v to 5.5v range. the constant current fast charge current for the adapter input mode is set by the r set resistor con- nected between the adpset and ground. refer to table 1 for recommended r set values for a desired constant current charge level. the precise charging function in the adapter mode may be read from the data pin and/or status leds. please refer to the battery charge status indication discussion in this datasheet for further details on data reporting. thermal loop control due to the integrated nature of the linear charging control pass device, a special thermal loop control system has been employed to maximize charging current under all operation conditions. the thermal management system measures the internal circuit die temperature and reduces the fast charge cur- rent when the device exceeds a preset internal temperature control threshold. once the thermal loop control becomes active, the fast charge cur- rent is initially reduced by a factor of 0.44. the initial thermal loop current can be estimated by the following equation: the thermal loop control re-evaluates the circuit die temperature every three seconds and adjusts the fast charge current back up in small steps to the full fast charge current level or until an equilibrium cur- rent is discovered and maximized for the given ambient temperature condition. the thermal loop controls the system charge level; therefore, the aat2550 will always provide the highest level of constant current possible in the fast charge mode for any given ambient temperature condition. adapter input charge inhibit and resume the aat2550 has an under-voltage lockout and power on reset feature so that the charger will sus- pend charging and shut down if the input supply to the adapter pin drops below the uvlo threshold. when power is re-applied to the adapter pin or the uvlo condition recovers and adp > v bat , the sys- tem charge control will assess the state of charge on the battery cell and will automatically resume charging in the appropriate mode for the condition of the battery. table 1: resistor values. enable / disable the aat2550 provides an enable function to con- trol the charger ic on and off. the enable (en) pin is active high. when pulled to a logic low level, the aat2550 will be shut down and forced into the sleep state. charging will be halted regardless of the battery voltage or charging state. when the device is re-enabled, the charge control circuit will automatically reset and resume charging functions with the appropriate charging mode based on the battery charge state and measured cell voltage. programming charge current the fast charge constant current charge level is programmed with a resistor placed between the adpset pin and ground. the accuracy of the fast charge, as well as the preconditioning trickle charge current, is dominated by the tolerance of the set resistor used. for this reason, 1% tolerance metal film resistors are recommended for the set resistor function. fast charge constant current levels from 100ma to 1a can be set by selecting the appropriate resistor value from table 1. the r set resistor should be con- nected between the adpset pin and ground. adp i ch r set (k ) 100 84.5 200 43.2 300 28.0 400 21.0 500 16.9 600 13.3 700 11.5 800 10.2 900 9.09 1000 8.06 aat2550 total power solution for portable applications 2550.2006.07.1.0 17 i tloop = i ch 0.44
figure 2: i fastcharge vs. r set . protection circuitry programmable watchdog timer the aat2550 contains a watchdog timing circuit for the adapter input charging mode. typically, a 0.1f ceramic capacitor is connected between the ct pin and ground. when a 0.1f ceramic capacitor is used, the device will time a shutdown condition if the trickle charge mode exceeds 25 minutes and a combined trickle charge plus fast charge mode of three hours. when the device transitions to the con- stant voltage mode, the timing counter is reset and will time out after three hours and shut down the charger (see table 2). table 2: summary for a 0.1f used for the timing capacitor. the ct pin is driven by a constant current source and will provide a linear response to increases in the timing capacitor value. thus, if the timing capac- itor were to be doubled from the nominal 0.1f value, the time-out durations would be doubled. if the programmable watchdog timer function is not needed, it can be disabled by connecting the ct pin to ground. the ct pin should not be left float- ing or un-terminated, as this will cause errors in the internal timing control circuit. the constant current provided to charge the timing capacitor is very small, and this pin is susceptible to noise and changes in capacitance value. therefore, the timing capacitor should be physical- ly located on the printed circuit board layout as closely as possible to the ct pin. since the accu- racy of the internal timer is dominated by the capacitance value, 10% tolerance or better ceram- ic capacitors are recommended. ceramic capacitor materials, such as x7r and x5r type, are a good choice for this application. over-voltage protection an over-voltage event is defined as a condition where the voltage on the bat pin exceeds the max- imum battery charge voltage and is set by the over- voltage protection threshold (v ovp ). if an over-volt- age condition occurs, the aat2550 charge control will shut down the device until voltage on the bat pin drops below the over-voltage protection thresh- old (v ovp ). the aat2550 will resume normal charg- ing operation after the over-voltage condition is removed. during an over-voltage event, the stat leds will report a system fault, and the actual fault condition may be read via the data pin signal. over-temperature shutdown the aat2550 has a thermal protection control cir- cuit which will shut down charging functions should the internal die temperature exceed the preset thermal limit threshold. battery temperature fault monitoring in the event of a battery over-temperature condi- tion, the charge control will turn off the internal pass device and report a battery temperature fault on the data pin function. the stat leds will also display a system fault. after the system recovers from a temperature fault, the device will resume charging operation. the aat2550 checks battery temperature before starting the charge cycle, as well as during all stages of charging. this is accomplished by moni- toring the voltage at the ts pin. this system is intended to use negative temperature coefficient thermistors (ntc), which are typically integrated into the battery package. most of the commonly mode time trickle charge (tc) time out 25 minutes trickle charge (tc) + 3 hours fast charge (cc) time out constant voltage (vc) mode 3 hours time out aat2550 total power solution for portable applications 18 2550.2006.07.1.0 r set (k 10 100 1000 10000 1 10 100 adp
used ntc thermistors in battery packs are approx- imately 10k at room temperature (25c). the ts pin has been specifically designed to source 80a of current to the thermistor. the volt- age on the ts pin that results from the resistive load should stay within a window from 330mv to 2.3v. if the battery becomes too hot during charg- ing due to an internal fault, the thermistor will heat up and reduce in value, pulling the ts pin voltage lower than the ts1 threshold, and the aat2550 will signal the fault condition. if the use of the ts pin function is not required by the system, it should be terminated to ground with a 10k resistor. battery charge status indication the aat2550 indicates the status of the battery under charge with two different systems. first, the device has two status led driver outputs. these two leds can indicate simple functions such as no battery charge activity, battery charging, charge complete, and charge fault. the aat2550 also pro- vides a bi-directional data reporting function so that a system microcontroller can interrogate the data pin and read any one of 13 system states. status indicator display simple system charging status states can be dis- played using one or two leds in conjunction with the stat1 and stat2 pins on the aat2550. these two pins are simple switches to connect the led cath- odes to ground. it is not necessary to use both dis- play leds if a user simply wants to have a single lamp to show "charging" or "not charging." this can be accomplished by using the stat1 pin and a sin- gle led. using two leds and both stat pins simply gives the user more information to the charging states. refer to table 3 for led display definitions. the led anodes should be connected to adp. the leds should be biased with as little current as nec- essary to create reasonable illumination; therefore, a ballast resistor should be placed between the led cathodes and the stat1/2 pins. led current consumption will add to the overall thermal power budget for the device package, so it is wise to keep the led drive current to a minimum. 2ma should be sufficient to drive most low-cost green or red leds. it is not recommended to exceed 8ma for driving an individual status led. the required ballast resistor value can be estimat- ed using the following formulas: for connection to the adapter supply: example: note: red led forward voltage (v f ) is typically 2.0v @ 2ma. green led forward voltage (v f ) is typically 3.2v @ 2ma. the four status led display conditions are described in table 3. aat2550 total power solution for portable applications 2550.2006.07.1.0 19 table 3: status led display conditions. event description stat1 stat2 charge disabled or low supply off off charge enabled without battery flash 1 flash 1 battery charging on off charge completed off on fault on on 1. flashing rate depends on output capacitance. r b(stat1) = = 1.75k 5.5v - 2.0v 2ma r b(stat1/2) = v adp - v f(led) i led(stat1/2)
digital charge status reporting the aat2550 has a comprehensive digital data reporting system by use of the data pin feature. this function can provide detailed information regarding the status of the charging system. the data pin is a bi-directional port which will read back a series of data pulses when the system microcon- troller asserts a request pulse. this single strobe request protocol will invoke one of 13 possible return pulse counts which the microcontroller can look up based on the serial report table shown in table 4. the data pin function is active low and should nor- mally be pulled high to v adp . this data line may also be pulled high to the same level as the high state for the logic i/o port on the system microcon- troller. in order for the data pin control circuit to generate clean, sharp edges for the data output and to maintain the integrity of the data timing for the system, the pull-up resistor on the data line should be low enough in value so that the data signal returns to the high state without delay. if too small a pull-up resistor is used, the strobe pulse from the system microcontroller could exceed the maximum pulse time and the data output control could issue false status reports. a 1.5k resistor is recommended when pulling the data pin high to 5.0v. if the data line is pulled high to a voltage level less than 5.0v, the pull-up resistor can be calculat- ed based on a recommended minimum pull-up cur- rent of 3ma. use the following formula: aat2550 total power solution for portable applications 20 2550.2006.07.1.0 table 4: serial data report table. figure 3: data pin application circuit. number data report status 1 chip over-temperature shutdown 2 battery temperature fault 3 over-voltage turn off 4 not used 5 adp watchdog time-out in battery condition mode 6 adp battery condition mode 7 adp watchdog time-out in constant current mode 8 adp thermal loop regulation in constant current mode 9 adp constant current mode 10 adp watchdog time-out in constant voltage mode 11 adp constant voltage mode 12 adp end of charging 23 data report error r pull-up v pull-up 3ma in out aat2550 status control data pin p gpio port out in gpio r pull_up 1.8v to 5.0v
data timing the system microcontroller should assert an active low data request pulse for minimum duration of 200ns; this is specified by the s qpulse . upon sens- ing the rising edge of the end of the data request pulse, the aat2550 status data control will reply the data word back to the system microcontroller after a delay defined by the data report time specification t data(rpt) . the period of the following group of data pulses will be defined by the t data specification. aat2550 total power solution for portable applications 2550.2006.07.1.0 21 timing diagram capacitor selection input capacitor in general, it is good design practice to place a decoupling capacitor between the adp pin and ground. an input capacitor in the range of 1f to 22f is recommended. if the source supply is unregulated, it may be necessary to increase the capacitance to keep the input voltage above the under-voltage lockout threshold during device enable and when battery charging is initiated. if the aat2550 adapter input is to be used in a sys- tem with an external power supply source, such as a typical ac-to-dc wall adapter, then a c in capaci- tor in the range of 10f should be used. a larger input capacitor in this application will minimize switching or power bounce effects when the power supply is "hot plugged." output capacitor the aat2550 only requires a 1f ceramic capac- itor on the bat pin to maintain circuit stability. this value should be increased to 10f or more if the battery connection is made any distance from the charger output. if the aat2550 is to be used in applications where the battery can be removed from the charger, such as in the case of desktop charging cradles, an output capacitor greater than 10f may be required to prevent the device from cycling on and off when no battery is present. sq s qpulse data system reset system start ck t sync t lat n=1 n=2 n=3 t off t data(rpt) = t sync + t lat < 2.5 p data t off > 2 p data p data
step-down converter functional description the aat2550 step-down converter is a high per- formance 600ma 1.4mhz monolithic power supply. it has been designed with the goal of minimizing external component size and optimizing efficiency over the complete load range. apart from the small bypass input capacitor, only a small l-c filter is required at the output. typically, a 4.7h inductor and a 4.7f ceramic capacitor are recommended (see table 5). the fixed output version requires only three exter- nal power components (c in , c out , and l). the adjustable version can be programmed with exter- nal feedback to any voltage, ranging from 0.6v to the input voltage. an additional feed-forward capacitor can also be added to the external feed- back with a 10f output capacitor for improved transient response (see c10 and c11 in figure 4). at dropout, the converter duty cycle increases to 100% and the output voltage tracks the input volt- age minus the r ds(on) drop of the p-channel high- side mosfet. the input voltage range is 2.7v to 5.5v. the con- verter efficiency has been optimized for all load conditions, ranging from no load to 600ma. the internal error amplifier and compensation pro- vides excellent transient response, load, and line regulation. soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. control loop the aat2550 step-down converter is a peak cur- rent mode control converter. the current through the p-channel mosfet (high side) is sensed for current loop control, as well as short-circuit and overload protection. a fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. the peak current mode loop appears as a voltage-pro- grammed current source in parallel with the output capacitor. the output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. internal loop compen- sation terminates the transconductance voltage error amplifier output. for fixed voltage versions, the error amplifier reference voltage is internally set to program the converter output voltage. for the adjustable output, the error amplifier reference is fixed at 0.6v. soft start / enable soft start limits the current surge seen at the input and eliminates output voltage overshoot. when pulled low, the enable input forces the aat2550 into a low-power, non-switching state. the total input current during shutdown is less than 1a. current limit and over-temperature protection for overload conditions, the peak input current is limited. to minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. thermal protection completely disables switching when internal dissipation becomes excessive. the junction over-temperature threshold is 140c with 15c of hysteresis. once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. under-voltage lockout internal bias of all circuits is controlled via the vin input. under-voltage lockout (uvlo) guarantees sufficient v in bias and proper operation of all inter- nal circuitry prior to activation. aat2550 total power solution for portable applications 22 2550.2006.07.1.0
step-down converter applications information inductor selection the step-down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50%. the output induc- tor value must be selected so the inductor current down slope meets the internal slope compensation requirements. the internal slope compensation for the adjustable and low-voltage fixed versions of the aat2550 is 0.24a/sec. this equates to a slope compensation that is 75% of the inductor current down slope for a 1.5v output and 4.7h inductor. this is the internal slope compensation for the adjustable (0.6v) version or low-voltage fixed ver- sions. when externally programming the 0.6v ver- sion to 2.5v, the calculated inductance is 7.5h. in this case, a standard 6.8h value is selected. for high-voltage fixed versions ( 2.5v), m = 0.48a/ sec. table 5 displays inductor values for the aat2550 fixed and adjustable options. manufacturer's specifications list both the inductor dc current rating, which is a thermal limitation, and the peak current rating, which is determined by the saturation characteristics. the inductor should not show any appreciable saturation under normal load conditions. some inductors may meet the peak and average current ratings yet result in excessive loss- es due to a high dcr. always consider the losses associated with the dcr and its effect on the total converter efficiency when selecting an inductor. the sumida 4.7h cdrh3d16 series inductor has a 105m dcr and a 900ma dc current rating. at full load, the inductor dc loss is 38mw, which gives a 4% loss in efficiency for a 600ma, 1.5v output. input capacitor select a 4.7f to 10f x7r or x5r ceramic capac- itor for the input. to estimate the required input capacitor size, determine the acceptable input rip- ple level (v pp ) and solve for c. the calculated value varies with input voltage and is a maximum when v in is double the output voltage. always examine the ceramic capacitor dc voltage coefficient characteristics when selecting the prop- er value. for example, the capacitance of a 10f, 6.3v, x5r ceramic capacitor with 5.0v dc applied is actually about 6f. aat2550 total power solution for portable applications 2550.2006.07.1.0 23 table 5: inductor values. configuration output voltage inductor 0.6v adjustable with 1v, 1.2v 2.2h external feedback 1.5v, 1.8v 4.7h 2.5v, 3.3v 6.8h fixed output 0.6v to 3.3v 4.7h c in(min) = 1 ?? - esr 4 f s ?? v pp i o ?? 1 - = for v in = 2 v o ?? v o v in v o v in 1 4 ?? 1 - ?? v o v in c in = v o v in ?? - esr f s ?? v pp i o 0.75 ? v o l = = 3 ? v o = 3 ? 2.5v = 7.5 h m 0.75 ? v o 0.24a sec a sec a a sec 0.75 ? v o m = = = 0.24 l 0.75 ? 1.5v 4.7 h a sec
the maximum input capacitor rms current is: the input capacitor rms ripple current varies with the input and output voltage and will always be less than or equal to half of the total dc load current. for v in = 2 v o the term appears in both the input voltage ripple and input capacitor rms current equations and is a maximum when v o is twice v in . this is why the input voltage ripple and the input capacitor rms current ripple are a maximum at 50% duty cycle. the input capacitor provides a low impedance loop for the edges of pulsed current drawn by the aat2550. low esr/esl x7r and x5r ceramic capacitors are ideal for this function. to minimize stray inductance, the capacitor should be placed as closely as possible to the ic. this keeps the high frequency content of the input current localized, minimizing emi and input voltage ripple. proper placement of the input capacitors (c4 and c5) can be seen in the evaluation board schemat- ic in figure 4. a laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation board input voltage pins. the induc- tance of these wires, along with the low-esr ceramic input capacitor, can create a high q net- work that may affect converter performance. this problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. errors in the loop phase and gain measurements can also result. since the inductance of a short pcb trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. in applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high esr tantalum or aluminum electrolytic input capacitor should be placed in parallel with the low esr bypass ceramic input capacitor (c6 of figure 4). this dampens the high q network and stabilizes the system. output capacitor the output capacitor limits the output ripple and provides holdup during large load transitions. a 4.7f to 10f x5r or x7r ceramic capacitor typi- cally provides sufficient bulk capacitance to stabi- lize the output during large load transitions and has the esr and esl characteristics necessary for low output ripple. the output voltage droop due to a load transient is dominated by the capacitance of the ceramic out- put capacitor. during a step increase in load cur- rent, the ceramic output capacitor alone supplies the load current until the loop responds. within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. the relationship of the output volt- age droop during the three switching cycles to the output capacitance can be estimated by: once the average inductor current increases to the dc load level, the output voltage recovers. the above equation establishes a limit on the minimum value for the output capacitor with respect to load transients. the internal voltage loop compensation also limits the minimum output capacitor value to 4.7f. this is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. increased output capacitance will reduce the crossover frequency with greater phase margin. aat2550 total power solution for portable applications 24 2550.2006.07.1.0 c out = 3 i load v droop f s ?? 1 - ?? v o v in v o v in i o rms(max) i 2 = ?? 1 - = d (1 - d) = 0.5 2 = ?? v o v in v o v in 1 2 ?? i rms = i o 1 - ?? v o v in v o v in
the maximum output capacitor rms ripple current is given by: dissipation due to the rms current in the ceramic output capacitor esr is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. adjustable output resistor selection for applications requiring an adjustable output volt- age, the 0.6v version can be externally pro- grammed. resistors r7 through r10 of figure 4 pro- gram the output to regulate at a voltage higher than 0.6v. to limit the bias current required for the exter- nal feedback resistor string while maintaining good noise immunity, the minimum suggested value for r7 and r9 is 59k . although a larger value will fur- ther reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. table 6 summarizes the resistor values for various output voltages with r7 and r9 set to either 59k for good noise immunity or 221k for reduced no load input current. table 6: adjustable resistor values for use with 0.6v step-down converter. the adjustable version of the aat2550, combined with an external feedforward capacitor (c10 and c11 in figure 4), delivers enhanced transient response for extreme pulsed load applications. the addition of the feedforward capacitor typically requires a larger output capacitor for stability. thermal considerations the aat2550 is available in a 4x4mm qfn pack- age, which has a typical thermal resistance of 28c/w when the exposed paddle is soldered to a printed circuit board (pcb) in the manner dis- cussed in the printed circuit board layout section of this datasheet. thermal resistance will vary with the pcb area, ground plane area, size and number of other adjacent components, and the heat they generate. the maximum ambient operating tem- perature is limited by either the design derating cri- teria, the over-temperature shutdown temperature, or the thermal loop charge current reduction con- trol. to calculate the junction temperature, sum the step-down converter losses with the battery charg- er losses. multiply the total losses by the package thermal resistance and add to the ambient temper- ature to determine the junction temperature rise. p sd is the total loss associated with both step-down converters and p c is the loss associated with the charger. the total losses will vary considerably depending on input voltage, load, and charging current. while charging a battery, the current capa- bility of the step-down converters is limited. r7, r9 = 59k r7, r9 = 221k v out (v) r8, r10 (k ) r8, r10 (k ) 0.8 19.6 75 0.9 29.4 113 1.0 39.2 150 1.1 49.9 187 1.2 59.0 221 1.3 68.1 261 1.4 78.7 301 1.5 88.7 332 1.8 118 442 1.85 124 464 2.0 137 523 2.5 187 715 3.3 267 1000 aat2550 total power solution for portable applications 2550.2006.07.1.0 25 t j(max) = (p sd + p c ) ja + t amb ?? ?? r8 = -1 r7 = - 1 59k = 88.5k v out v ref ?? ?? 1.5v 0.6v 1 23 v out (v in(max) - v out ) rms(max) i l f s v in(max) =
step-down converter losses there are three types of losses are associated with the aat2550 step-down converter: switching losses (t sw f s ), conduction losses (i 2 r ds(on) ), and qui- escent current losses (i q v in ). at full load, assum- ing continuous conduction mode, a simplified form of the step-down converter losses is: aat2550 total power solution for portable applications 26 2550.2006.07.1.0 for the condition where one channel is in dropout at 100% duty cycle (i oa ), the step-down converter dissipation is: p sd = step-down converter dissipation v in = converter input voltage r ds(on)h = high side mosfet on resistance r ds(on)l = low side mosfet on resistance v oa = converter a output voltage v ob = converter b output voltage i oa = converter a load current i ob = converter b load current i q = converter quiescent current t sw = switching time estimate f s = converter switching frequency always use the r ds(on) and quiescent current value that corresponds to the applied input voltage. battery charger losses the maximum battery charger loss is: p c = total charger dissipation v adp = adapter voltage v min = preconditioning voltage threshold i ch = programmed charge current i qc = charger quiescent current consumed by the charger for an application where no load is applied to the step-down converters and the charger current is set to 1a with v adp = 5.0v, the maximum charger dissipation occurs at the preconditioning voltage threshold v min . the charger thermal loop begins reducing the charge current at a 110c junction temperature (t loop_in ). the ambient temperature at which the charger thermal loop begins reducing the charge current is: therefore, under the given conditions, the aat2550 battery charger will enter the thermal loop charge current reduction at an ambient tem- perature greater than 54c. p sd = + ( t sw f s ( i oa + i ob ) + 2 i q ) v in i oa 2 (r ds(on)h v oa + r ds(on)l (v in - v oa )) + i ob 2 (r ds(on)h v ob + r ds(on)l (v in - v ob )) v in t a = t loop_in - ja p c = 110c - (28c/w) 2w = 54c p c = (v adp - v min ) i ch + v adp i qc = (5.0v - 3.0v) 1a + 5.0v 0.74m a = 2w p c = (v adp - v min ) i ch + v adp i qc p sd = i oa 2 r ds(on)h + ( t sw f s i ob + 2 i q ) v in + i ob 2 (r ds(on)h v ob + r ds(on)l (v in - v ob ) ) v in
total power loss examples the most likely high power scenario is when the charger and step-down converter are both opera- tional and powered from the adapter. to examine the step-down converter maximum current capabil- ity for this condition, it is necessary to determine the step-down converter mosfet r ds(on) , quies- cent current, and switching losses at the adapter voltage level (5v). this example shows that with a 600ma battery charge current, the buck converter output current capability is limited 400ma. this lim- its the junction temperature to 110c and avoids the thermal loop charge reduction at a 70c ambi- ent temperature. conditions: v oa 2.5v @ step-down converter a 400ma v ob 1.8v @ step-down converter b 400ma i q 70a converter quiescent current v in = 5.0v charger and step-down v adp converter input voltage v min 3.0v battery preconditioning threshold voltage i ch 0.6a battery charge current i op 0.75ma charger operating current aat2550 total power solution for portable applications 2550.2006.07.1.0 27 the step-down converter load current capability is greatest when the battery charger is disabled. the following example demonstrates the junction tem- perature rise for conditions where the battery charg- er is disabled and full load is applied to both con- verter outputs at the nominal battery input voltage. conditions: v o1 2.5v @ step-down converter a 600ma v o2 1.8v @ step-down converter b 600ma i q 70a converter quiescent current v in 3.6v charger and step-down converter input voltage i ch = 0a charger disabled i op t j(max) = t amb + ja p loss = 70c + (28c/w) 1.38w = 108c p total = + ( t sw f s ( i oa + i ob ) + 2 i q ) v in + (v adp - v min ) i ch + v adp i op + 2 ( 5ns 1.4mhz 0.4a + 70a) 5.0v + (5.0v - 3.0v) 0.6a + 5.0v 0.75ma = 1.38w = i oa 2 (r ds(on)h v oa + r ds(on)l (v in - v oa )) + i ob 2 (r ds(on)h v ob + r ds(on)l (v in - v ob )) v in 0.4a 2 (0.475 2.5v + 0.45 (5.0v - 2.5v)) + 0.4a 2 (0.475 1.8v + 0.45 (5.0v - 1.8v)) 5.0v
printed circuit board layout use the following guidelines to ensure a proper printed circuit board layout. 1. step-down converter bypass capacitors (c4 and c5 in figure 4) must be placed as close as possible to the step-down converter inputs. 2. the connections from the lxa and lxb pins of the step-down converters to the output induc- tors should be kept as short as possible. this is a switching node, so minimizing the length will reduce the potential of this noisy trace interfering with other high impedance noise sensitive nodes. 3. the feedback trace should be separate from any power trace and connected as closely as possible to the load point. sensing along a high current load trace will degrade the dc load reg- ulation. if external feedback resistors are used, they should be placed as closely as possible to the fb pin. this prevents noise from being cou- pled into the high impedance feedback node. 4. the resistance of the trace from the load return to gnd should be kept to a minimum. this min- imizes any error in dc regulation due to differ- ences in the potential of the internal signal ground and the power ground. 5. for good thermal coupling, vias are required from the pad for the qfn paddle to the ground plane. via diameters should be 0.3mm to 0.33mm and positioned on a 1.2mm grid. avoid close placement to other heat generating devices. 6. minimize the trace impedance from the battery to the bat pin. the charger output is not remotely sensed, so any drop in the output across the bat output trace feeding the battery will add to the error in the eoc battery voltage. to minimize voltage drops on the pcb, main- tain an adequate high current carrying trace width. aat2550 total power solution for portable applications 28 2550.2006.07.1.0 t j(max) = t amb + ja p loss = 85c + (28c/w) 0.443w = 97c p total = + ( t sw f s ( i oa + i ob ) + 2 i q ) v in + (v adp - v min ) i ch + v adp i op + 2 ( 5ns 1.4mhz 0.4a + 70a) 3.6v = 0.443w = i oa 2 (r ds(on)h v oa + r ds(on)l (v in - v oa )) + i ob 2 (r ds(on)h v ob + r ds(on)l (v in - v ob )) v in 0.6a 2 (0.58 2.5v + 0.56 (3.6v - 2.5v)) + 0.2a 2 (0.58 1.8v + 0.56 (3.6v - 1.8v)) 3.6v
aat2550 total power solution for portable applications 2550.2006.07.1.0 29 figure 4: aat2550 evaluation board schematic. 1 3 2 voa tb2 1 2 adapter input tb3 gnd sw1 data strobe stat1 red d1 stat2 green d2 l2 4.7h l1 6.8h ena 1 lxa 2 pgnd 3 data 4 n/c 5 adpset 6 n/c 7 bat 8 adp 9 agnd 10 agnd 11 enbat 12 ts 13 stat2 14 stat1 15 ct 16 pgnd 17 lxb 18 enb 19 inb 20 fbb 21 agnd 22 fba 23 ina 24 aat2550 u1 c8 4.7f 4.7f c9 10f c4 10f c5 1 3 2 charger enable tb4 1 3 2 tb5 battery adp bat gnd ts 10f c3 0.1f c12 118k r10 r9 59.0k 59.0k r7 r8 267k c11 n/a n/a c10 4.7k r1 4.7k r2 8.06k r6 j3 vin vob j5 voa ct j7 j2 gnd j1 gnd j8 gnd 1 3 2 vob tb1 100f c6 1k r3 0.01f c14 lxa lxb j4 10k r4
figure 5: aat2550 evaluation board figure 6: aat2550 evaluation board top side layout. bottom side layout. table 7: aat2550 evaluation board bill of materials. reference qty. description designator manufacturer part number 1 conn. term block 2.54mm 2 pos adapter input phoenix contact 1 conn. term block 2.54mm 3 pos battery output phoenix contact 3 ceramic capacitor 10f 10%, 10v, c3,c4,c5 murata x5r, 0805 2 ceramic capacitor 4.7f 10%, 6.3v, c8,c9 murata x5r, 0805 1 ceramic capacitor 0.1f 25v 10% c12 vishay x5r 0603 1 tantalum capacitor 100f, 6.3v, case c c6 vishay 2 optional ceramic capacitor 100pf, 0402, cog c10, c11 vishay 2 ferrite shielded inductor cdrh3d16 l1, l2 sumida 2 4.7k, 5%, 1/16w, 0402 r1,r2 vishay 1 1.0k, 5%, 1/16w, 0402 r3 vishay 1 8.06k, 1%, 1/16w, 0402 r6 vishay 2 59.0k, 1%, 1/16w, 0402 r7,r9 vishay 1 1%, 1/16w, 0402 r10 vishay 1 1%, 1/16w, 0402 r8 vishay 1 10k, 5%, 1/16w, 0402 r4 vishay 1 red led, 1206 d1 chicago miniature lamp cmd15-21src/tr8 1 green led, 1206 d2 chicago miniature lamp cmd15-21src/tr8 1 switch tact 6mm spst h = 5.0mm sw1 itt industries/c&k div ckn9012-nd 1 aat2550 total power solution for portable u1 advanced analogic AAT2550ISK-CAA-T1 applications technologies aat2550 total power solution for portable applications 30 2550.2006.07.1.0
table 8: typical surface mount inductors. table 9: surface mount capacitors. table 10: evaluation board component values. adjustable version (0.6v device) r7, r9 = 59k r7, r9 = 221k 1 v out (v) r8, r10 (k ) r8, r10 (k ) l1, l2 (h) 0.8 19.6 75.0 2.2 0.9 29.4 113 2.2 1.0 39.2 150 2.2 1.1 49.9 187 2.2 1.2 59.0 221 2.2 1.3 68.1 261 2.2 1.4 78.7 301 4.7 1.5 88.7 332 4.7 1.8 118 442 4.7 1.85 124 464 4.7 2.0 137 523 6.8 2.5 187 715 6.8 3.3 267 1000 6.8 fixed version r7, r9 not used v out (v) r8, r10 (k ) l1, l2 (h) 0.6-3.3v 0 4.7 manufacturer part number value voltage temp. co. case murata grm219r61a475ke19 4.7f 10v x5r 0805 murata grm21br60j106ke19 10f 6.3v x5r 0805 murata grm21br60j226me39 22f 6.3v x5r 0805 inductance max dc dcr size (mm) manufacturer part number (h) current (a) ( ) lxwxh type sumida cdrh3d16-2r2 2.2 1.20 0.072 3.8x3.8x1.8 shielded sumida cdrh3d16-4r7 4.7 0.90 0.105 3.8x3.8x1.8 shielded sumida cdrh3d16-6r8 6.8 0.73 0.170 3.8x3.8x1.8 shielded murata lqh2mcn4r7m02 4.7 0.40 0.80 2.0x1.6x0.95 non-shielded murata lqh32cn4r7m23 4.7 0.45 0.20 2.5x3.2x2.0 non-shielded coilcraft lpo3310-472 4.7 0.80 0.27 3.2x3.2x1.0 1mm coiltronics sd3118-4r7 4.7 0.98 0.122 3.1x3.1x1.85 shielded coiltronics sd3118-6r8 6.8 0.82 0.175 3.1x3.1x1.85 shielded coiltronics sdrc10-4r7 4.7 1.30 0.122 5.7x4.4x1.0 1mm shielded aat2550 total power solution for portable applications 2550.2006.07.1.0 31 1. for reduced quiescent current, r7 and r9 = 221k .
step-down converter design example specifications v o1 = 2.5v @ 400ma (adjustable using 0.6v version), pulsed load i load = 300ma v o2 = 1.8v @ 400ma (adjustable using 0.6v version), pulsed load i load = 300ma v in = 2.7v to 4.2v (3.6v nominal) f s = 1.4mhz t amb = 85c 2.5v v o1 output inductor (see table 5) for sumida inductor cdrh3d16, 6.8h, dcr = 170m . 1.8v v o2 output inductor (see table 5) for sumida inductor cdrh3d16, 4.7h, dcr = 105m . aat2550 total power solution for portable applications 32 2550.2006.07.1.0 v o2 v o2 1.8 v 1.8v i2 = ? 1 - = ? 1 - = 156ma l ? f s v in 4.7 h ? 1.4mhz 4.2v i pk2 = i o2 + i2 = 0.4a + 0.078a = 0.48a 2 p l2 = i o2 2 ? dcr = 0.4a 2 ? 105m = 17mw ? ? ? ? ? ? ? ? l2 = 3 ? v o2 = 3 ? 1.8v = 5.4 h sec a sec a v o v o1 2.5 v 2.5v i1 = ? 1 - = ? 1 - = 106ma l1 ? f s v in 6.8 h ? 1.4mhz 4.2v i pk1 = i o1 + i1 = 0.4a + 0.053a = 0.453a 2 p l1 = i o1 2 ? dcr = 0.45 2 ? 170m = 0.45 2 a 2 ? 170m = 34mw ? ? ? ? ? ? ? ? l1 = 3 ? v o1 = 3 ? 2.5v = 7.5 h sec a sec a
2.5v output capacitor 1.8v output capacitor input capacitor input ripple v pp = 25mv. aat2550 total power solution for portable applications 2550.2006.07.1.0 33 i o1 + i o2 rms(max) i p = esr i rms 2 = 5m (0.4a) 2 = 0.8mw 2 = = 0.4arms c in = = = 6.8 f 1 ?? - esr 4 f s ?? v pp i o1 + i o2 1 ?? - 5m 4 1.4mhz ?? 25mv 0.8a 1 23 1 1.8v (4.2v - 1.8v) 4.7 h 1.4mhz 4.2v 23 rms(max) i l f s v in(max) = 3 i load v droop f s 3 0.3a 0.2v 1.4mhz c out = = = 3.2 f = 45marms (v out ) (v in(max) - v out ) = p esr = esr i rms 2 = 5m (45ma) 2 = 10 w 1 23 1 2.5v (4.2v - 2.5v) 10 h 1.4mhz 4.2v 23 rms(max) i l f s v in(max) = 3 i load v droop f s 3 0.3a 0.2v 1.4mhz c out = = = 3.2 f = 21marms (v out ) (v in(max) - v out ) = p esr = esr i rms 2 = 5m (21ma) 2 = 2.2 w
aat2550 total power solution for portable applications 34 2550.2006.07.1.0 ordering information voltage package converter 1 converter 2 marking 1 part number (tape and reel) 2 qfn44-24 0.6v 0.6v rjxyy AAT2550ISK-CAA-T1 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . legend voltage code adjustable a (0.6v) 0.9 b 1.2 e 1.5 g 1.8 i 1.9 y 2.5 n 2.6 o 2.7 p 2.8 q 2.85 r 2.9 s 3.0 t 3.3 w 4.2 c all analogictech products are offered in pb-free packaging. the term ?pb-free? means semiconductor products that are in compliance with current rohs standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. for more information, please visit our website at http://www.analogictech.com/pbfree.
aat2550 total power solution for portable applications 2550.2006.07.1.0 35 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737-4600 fax (408) 737-4611 qfn44-24 all dimensions in millimeters. ? advanced analogic technologies, inc. analogictech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an analogictech pr oduct. no circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. analogictech reserves the right to make changes to their products or specifi cations or to discontinue any product or service without notice. customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information b eing relied on is current and complete. all products are sold sub- ject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. analogictech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with anal ogictech?s standard warranty. testing and other quality con- trol techniques are utilized to the extent analogictech deems necessary to support this warranty. specific testing of all param eters of each device is not necessarily performed. analogictech and the analogictech logo are trademarks of advanced analogic technologies incorporated. all other brand and produ ct names appearing in this document are regis- tered trademarks or trademarks of their respective holders. 4.000 45 pin 1 dot by marking 4.000

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