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general description the aat3685 batterymanager? is a highly inte- grated single cell lithium-ion/polymer battery charg- er ic designed to operate with usb port or line adapter inputs. it requires the minimum number of external components. the aat3685 precisely regulates battery charge volt- age and current for 4.2v lithium-ion/polymer battery cells. regardless of the type of input power source (usb or adapter), the aat3685 can be programmed for two separate constant current charge levels up to 1a. an optional charge reduction loop is built in to allow users to charge the battery with available cur- rent from the charge supply, while keeping the port voltage regulated. battery temperature and charge state are fully monitored for fault conditions. in the event of an over-voltage or over-temperature failure, the device will automatically shut down, thus protecting the charging device, control system, and the bat- tery under charge. status monitor output pins are provided to indicate the battery charge status by directly driving two external leds. a serial interface output is available to report any one of 14 various status states to a microcontroller. the aat3685 is available in a pb-free, thermally- enhanced, space-saving 12-pin 3x3mm tdfn package and is rated over the -40c to +85c tem- perature range. features ? adapter or usb charger ? programmable up to 1a max ? 4.0v to 5.5v input voltage range ? high level of integration with internal: ? charging device ? reverse blocking diode ? current sensing ? automatic recharge sequencing ? charge reduction loop ? battery temperature monitoring ? full battery charge auto turn-off ? over-voltage protection ? emergency thermal protection ? power on reset and soft start ? serial interface status reporting ? 12-pin 3x3mm tdfn package applications ? cellular telephones ? digital still cameras ? hand-held pcs ? mp3 players ? personal data assistants (pdas) ? other lithium-ion/polymer battery-powered devices aat3685 lithium-ion/polymer battery charger typical application 3685.2006.10.1.3 1 batterymanager ? aat3685 c2 10 f batt- temp a dapter or usb input battery pack serial data adp/usb pwrsel gnd ts bat batt+ input hi/lo select stat1 r seth seth r setl setl chr en stat2 data enable
pin descriptions pin configuration tdfn33-12 (top view) pin # name type function 1 adp/usb in line adapter or usb power supply input. 2 bat in/out battery charging and sensing. 3 gnd ground ground connection. 4 chr in/out resistor divider to set usb voltage regulation for charge reduction mode. leave this pin open for default 4.5v usb regulation point. tie to adp/usb pin to disable this function. 5 en in enable pin. logic high enables the ic. 6 ts in/out connect to 10k ntc thermistor. 7 data in/out status report to microcontroller via serial interface, open-drain. 8 stat2 out battery charge status indicator pin to drive an led: active low, open-drain. 9 stat1 out battery charge status indicator pin to drive an led: active low, open-drain. 10 pwrsel in when adp/usb is present, use this pin to toggle between seth and setl charging levels. 11 setl in/out connect resistor here to set charge current for low-current port. 12 seth in/out connect resistor here to set charge current for high-current port. ep exposed paddle (bottom); connect to gnd directly beneath package. aat3685 lithium-ion/polymer battery charger 2 3685.2006.10.1.3 a dp/usb bat gnd 1 chr en ts seth setl pwrsel stat1 stat2 data 2 3 4 5 6 12 11 10 9 8 7
aat3685 feature options absolute maximum ratings 1 thermal information 2 symbol description value units ja maximum thermal resistance (3x3mm tdfn) 50 c/w p d maximum power dissipation 2.0 w symbol description value units v p adp/usb input voltage, <30ms, duty cycle <10% -0.3 to 7.0 v v p adp/usb input voltage, continuous -0.3 to 6.0 v v n bat, pwrsel, seth, setl, stat1, stat2, data, ts, chr, en -0.3 to v p + 0.3 v t j operating junction temperature range -40 to 150 c t lead maximum soldering temperature (at leads) 300 c internal pull-up can leave product resistor on en pin ts pin open aat3685 no no aat3685-1 yes yes aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 3 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at c ondi- tions other than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any one time. 2. mounted on an fr4 board.
electrical characteristics 1 v adp = 5v, t a = -25c to +85c, unless otherwise noted. typical values are at t a = 25c. symbol description conditions min typ max units operation adp/usb input voltage range 4.0 5.5 v v uvlo under-voltage lockout rising edge 3.0 v under-voltage lockout hysteresis 150 mv i op operating current cc charge current = 500ma 0.75 1.5 ma i sleep sleep mode current aat3685: v bat = 4.25v 0.3 1.0 a aat3685-1: v bat = 4.25v 1 3 i leakage reverse leakage current from v bat = 4v, adp/usb pin 1.0 a bat pin open voltage regulation v bat _ eoc 1 end of charge voltage accuracy 4.158 4.2 4.242 v v bat /v bat eoc voltage tolerance 0.5 % v min preconditioning voltage threshold 2.8 3.0 3.15 v v rch battery recharge voltage threshold v bat _ eoc - 0.1 v v adp/usb _ chr charge reduction regulation no connection on chr pin 4.3 4.5 4.64 v v chr chr pin voltage accuracy 1.9 2.0 2.1 v current regulation i ch charge current 50 1000 ma i ch /i ch charge current regulation 10 % tolerance v seth seth pin voltage cc mode 2.0 v v setl setl pin voltage cc mode 2.0 v k iuh current set factor: i charge /i seth 2000 k iul current set factor: i charge /i setl 2000 charging devices r ds(on)u charging mosfet transistor v in = 5.5v 0.4 0.5 0.65 on resistance aat3685 lithium-ion/polymer battery charger 4 3685.2006.10.1.3 1. the aat3685 output charge voltage is specified over the 0 to 70c ambient temperature range; operation over the -25c to +8 5c temperature range is guaranteed by design.
electrical characteristics 1 v adp = 5v, t a = -25c to +85c, unless otherwise noted. typical values are at t a = 25c. symbol description conditions min typ max units logic control / protection v pwrsel(h) input high threshold 1.6 v v pwrsel(l) input low threshold 0.4 v v en(h) input high threshold 1.6 v v en(l) input low threshold 0.4 v i en(h) en input current aat3685-1 only, v en = 5v 10 a v s tat output low voltage stat pin sinks 4ma 0.4 v i s tat stat pin current sink capability 8.0 ma v ovp over-voltage protection threshold 4.4 v i tk /i chg pre-charge current for seth mode 10 % for setl mode 50 i term /i chg charge termination threshold current for seth mode 7.5 % i term /i chg charge termination threshold current for setl mode 35 % i ts current source from ts pin 70 80 90 a ts1 ts hot temperature fault threshold 310 330 350 mv hysteresis 15 ts2 ts cold temperature fault threshold 2.2 2.3 2.4 v hysteresis 10 mv i_data data pin sink current data pin is active low state 3.0 ma v data(h) input high threshold 1.6 v v data)(l) input low threshold 0.4 v sq pulse status request pulse width status request 200 ns t period system clock period 50 s f d ata data output frequency 20 khz t ovsd over-temperature shutdown threshold 145 c aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 5 1. the aat3685 output charge voltage is specified over the 0 to 70c ambient temperature range; operation over the -25c to +8 5c temperature range is guaranteed by design.
typical characteristics aat3685 lithium-ion/polymer battery charger 6 3685.2006.10.1.3 preconditioning charge current vs. temperature (seth; seth = 3.83k ) temperature ( 80 90 100 110 120 -50 -25 0 25 50 75 100 preconditioning threshold voltage vs. temperature temperature ( 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 vs. temperature temperature ( 4.158 4.179 4.200 4.221 4.242 -50 -25 0 25 50 75 100 recharge voltage vs. temperature temperature ( 4.040 4.050 4.060 4.070 4.080 4.090 4.100 4.110 4.120 4.130 4.140 -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 5.25 5.5 i fastcharge vs. r set r set (k 10 100 1000 10000 1 10 100 1000 setl seth
typical characteristics aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 7 fast charge current vs. supply voltage (seth; seth = 3.83k ) supply voltage (v) i ch (ma) 0 200 400 600 800 1000 1200 4.40 4.50 4.60 4.70 4.80 4.90 5.0 0 0 c 25 c 70 c fast charge current vs. supply voltage (setl; setl = 40.2k ) supply voltage (v) i ch (ma) 0 20 40 60 80 100 120 4 4.5 5.5 6.5 56 v bat = 3.3v v bat = 3.5v v bat = 3.9v fast charge current vs. supply voltage (seth; seth = 3.83k ) supply voltage (v) i ch (ma) 0 200 400 600 800 1000 1200 4 4.25 4.5 4.75 5 5.25 5.5 5.75 6 v bat = 3.3v v bat = 3.9v v bat = 3.5v charging current vs. battery voltage (setl; setl = 40.2k ) battery voltage (v) i ch (ma) 0 20 40 60 80 100 120 2.5 3 3.5 4 4. 5 charging current vs. battery voltage (seth; seth = 3.83k 0 200 400 600 800 1000 1200 2.5 3 3.5 4 4.5 fast charge current vs. temperature (seth; seth = 3.83k ) temperature ( 900 920 940 960 980 1000 1020 1040 1060 1080 1100 -50 -25 0 25 50 75 100
typical characteristics aat3685 lithium-ion/polymer battery charger 8 3685.2006.10.1.3 v ih vs. supply voltage pwrsel (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 5.2 5.4 5.6 5.8 6 -40 c +25 c +85 c v il vs. supply voltage en pin (falling) supply voltage (v) v il (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 5.2 5.4 5.6 5.8 6 -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 5.2 5.4 5.6 5.8 6 -40 c +25 c +85 c charge current vs. time (seth; seth = 3.83k ) time (sec) v bus (400mv/div) charge current (400ma/div) peripheral current consumption (400ma/div) 01234 56 78910 charge reduction mode activated supply current vs. seth resistor seth resistor (k ) i q (ma) 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 1 10 100 100 0 constant current pre-conditioning v il vs. supply voltage pwrsel (falling) supply voltage (v) v il (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 5.2 5.4 5.6 5.8 6 -40 c +25 c +85 c
typical characteristics aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 9 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 75 100
functional block diagram aat3685 lithium-ion/polymer battery charger 10 3685.2006.10.1.3 functional description the aat3685 is a highly integrated single cell lithi- um-ion/polymer battery charger ic designed to operate from adapter or usb port v bus supplies, while requiring a minimum number of external components. the device precisely regulates bat- tery charge voltage and current for 4.2v lithium- ion/polymer battery cells. the aat3685 is specifically designed for being powered from a usb port v bus supply, but it can also be powered from any input voltage source capable supplying 4.5v to 5.5v for loads up to 1a. the aat3685 constant charge current can be externally programmed for two levels, seth and setl, for maximum constant current charge levels up to 1a. the seth/l mode has an automatic charge reduction loop control to allow users to charge the battery with limited available current from a port while maintaining the regulated port voltage. this system assures the battery charge function will not overload the port while charging if other system demands also share power with the respective port supply. status monitor output pins are provided to indicate the battery charge status by directly driving two external leds. a serial interface output is available to report 14 various charge states to a system microcontroller. battery temperature and charge state are fully monitored for fault conditions. in the event of an over-voltage or over-temperature failure, the device will automatically shut down, thus protecting the charging device, control system, and the bat- tery under charge. in addition to internal charge controller thermal protection, the aat3685 also provides 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 during charging. all fault events are reported to the user either by the simple status leds or via the data pin function. charge control current compare reverse blocking cv/ precharge a dp/usb pwrsel constant current ba t uvlo over- temperature protect charge status stat2 stat1 ts window comparator 80 a seth setl serial data data gnd charge reduction loop chr en ic enable
charging operation the aat3685 has four basic modes for the battery charge cycle and is powered from the input: pre-con- ditioning/trickle charge; constant current/fast charge; constant voltage; and end of charge. for reference, figure 1 shows the current versus voltage profile during charging phases. battery preconditioning before the start of charging, the aat3685 checks several conditions in order to assure a safe charging environment. the input supply must be above the minimum operating voltage, or under-voltage lockout threshold (v uvlo ), for the charging sequence to begin. in addition, the cell 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 aat3685 checks the state of the battery. if the cell voltage is below the preconditioning voltage threshold (v min ), the aat3685 begins preconditioning the cell. the battery preconditioning trickle charge current is equal to the fast charge constant current divided by 10. for example, if the programmed fast charge current is 500ma, then the preconditioning mode (trickle charge) current will be 50ma. cell precon- ditioning is a safety precaution for a deeply dis- charged battery and also aids in limiting power dis- sipation in the pass transistor when the voltage across the device is at the greatest potential. fast charge / constant current charging battery cell preconditioning continues until the volt- age on the bat pin exceeds the preconditioning voltage threshold (v min ). at this point, the aat3685 begins the constant current fast charging phase. the fast charge constant current (i cc ) amplitude is determined by the selected charge mode seth or setl and is programmed by the user via the r seth and r setl resistors. the aat3685 remains in con- stant current charge mode until the battery reaches the voltage regulation point, v bat . constant voltage charging the system transitions to a constant voltage charg- ing mode when the battery voltage reaches output charge regulation threshold (v bat ) 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 battery cell 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 volt- age 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 charg- er will also automatically enter power-saving sleep mode. only consuming an ultra-low 0.3 a in sleep mode (1 a for aat3685-1), the aat3685 mini- mizes battery drain when it is not charging. this feature is particularly useful in applications where the input supply level may fall below the battery charge or under-voltage lockout level. in such cases where the aat3685 input voltage drops, the device will enter the sleep mode and automatically resume charging once the input supply has recov- ered from its fault condition. aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 11 figure 1: current vs. voltage profile during charging phases. constant current charge phase constant voltage charge phase preconditioning trickle charge phase charge complete voltage constant current mode voltage threshold regulated current trickle charge and termination threshold i = cc / 10 i = max cc
system operation flow chart aat3685 lithium-ion/polymer battery charger 12 3685.2006.10.1.3 current phase test v eoc >v bat no no no no no yes yes yes yes yes 0 1 no yes no yes no switch on uvlo v p > v uvlo input power yes input detect pwrsel= ? setl current loop seth current loop power on reset sleep mode fault conditions monitor ov, ot battery temperature monitor v ts1 < ts < v ts2 shut down mode battery temp. fault input voltage regulation enable recharge test v rch > v bat preconditioning test v min > v bat low current conditioning charge current charging mode charge current reduction port voltage test v adp/usb < v adp/usb_chr voltage charging mode voltage phase test i bat > i term charge completed
application information usb system power charging the usb charge mode provides two programma- ble fast charge levels up to 1a for each, seth and setl. the seth or setl modes may be exter- nally selected by the select pin (pwrsel). when the pwrsel pin is connected to a logic high level, the seth level will be active. conversely, when pwrsel is pulled to a logic low level (ground), the setl level will be used for fast charging. these two charge levels may be user programmed to any level between 50ma and 1a by selecting the appro- priate resistor values for r seth and r setl . refer to table 1 for recommended r seth and r setl values for the desired input constant current charge levels. charge reduction in many instances, product system designers do not know the real properties of a potential port to be used to supply power to the battery charger. typical powered usb ports commonly found on desktop and notebook pcs should supply up to 500ma. in the event a port being used to supply the charger is unable to provide the programmed fast charge current, or if the system under charge must also share supply current with other func- tions, the aat3685 will automatically reduce usb fast charge current to maintain port integrity and protect the host system. the charge reduction system becomes active when the voltage on the input falls below the charge reduction threshold (v adp/usb_chr ), which is typical- ly 4.5v. regardless of which charge function is selected (seth or setl), the charge reduction system will reduce the fast charge current level in a linear fashion until the voltage sensed on the input recovers above the charge reduction threshold volt- age. the charge reduction threshold (v adp/usb_chr ) may be externally set to a value lower than 4.5v by placing a resistor divider network between v adp/usb and ground with the center connected to the chr pin. the charge reduction feature may be disabled by connecting a 10k resistor from the chr pin directly to the adp/usb input pin. the following equation may be used to approximate a usb charge reduction threshold below 4.5v: eq. 1: where r11/r12 << 1m . aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 13 table 1: recommended r set values. figure 2: internal equivalent circuit for the chr pin. seth setl seth setl i cc r set (k )r set (k )i cc r set (k )r set (k ) 50 86.6 86.6 500 8.06 8.06 75 57.6 57.6 600 6.65 6.65 100 42.2 42.2 700 5.62 5.62 200 21.0 20.5 800 4.87 4.87 300 13.7 13.7 900 4.32 4.32 400 10.2 10.2 1000 3.83 3.83 v adp/usb_chr = 2.0v r12 r12 + r11 1.025m 825k r11 r12 v chr = 2.0 v v adp/usb adp/usb chr
input charge inhibit and resume the aat3685 uvlo and power on reset feature will function when the input pin voltage level drops below the uvlo threshold. at this point, the charg- er will suspend charging and shut down. when power is re-applied to the adp/usb pin or the uvlo condition recovers, the system charge con- trol 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. single path charging from a line adapter or usb source most usb charging applications limit charging cur- rent to 500ma due to the limitations of a usb port as a power source. the aat3685 is capable of, and may be programmed for, constant current charge levels up to 1a. thus, charging operation is not just restricted to use with usb port supplies. any power source may be used within the operat- ing voltage limits as specified in the electrical characteristics section of this datasheet. this makes the aat3685 perfect for applications that only have one input path, but may access either a line adapter source or a usb port supply. in order to fully utilize the power capacity from a line adapter or usb port supply, program the seth charge rate according to the highest charging cur- rent capacity of the two possible sources, providing that neither supply exceeds 1a. a lower charge level may be set with the setl charge rate and selection of the higher or lower charge rate is con- trolled via the pwrsel function. if the pro- grammed charge rate is greater than the current source capacity, there is little danger of system fail- ure because the aat3685 charge reduction loop will activate to automatically reduce the charging current and maintain a supply voltage set by the chr threshold. if the input supply is incapable of maintaining an input voltage greater than the under- voltage lockout level of the aat3685, the charge control will suspend charging until the source sup- ply is capable of supplying the minimum input cur- rent to charge. at this point, the aat3685 will auto- matically resume charging in the appropriate mode based on the battery cell voltage. in case of an over-temperature condition with a high charge cur- rent and large input-to-battery voltage difference, the device will cycle from charging to thermal shut- down and re-charge after temperature drops suffi- ciently, until the battery is charged to 4.2v. enable / disable the aat3685 provides an enable function to con- trol the charger ic on and off. the enable (en) pin is an active high. when pulled to a logic low level, the aat3685 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 for the adp/usb input is programmed with set resistors placed between the seth and setl pins and ground. the accuracy of the fast charge, as well as the preconditioning trickle charge current, is domi- nated by the tolerance of the set resistors used. for this reason, 1% tolerance metal film resistors are recommended for programming the desired con- stant current level. the fast charge constant current charge control provides for two current set levels, seth and setl. the pwrsel pin is used to select the high or low charge current levels. when the pwrsel pin is pulled to a voltage level above the v pwrsel(h) threshold, the seth current level will be selected. conversely, this pin should be pulled below the v pwrsel(l) to enable the setl charge level. these two charge levels may be set to any level between 50ma and 1a, depending upon the system design requirements for a given charge application. refer to table 1 and figure 3 for recommended r seth and r setl values. aat3685 lithium-ion/polymer battery charger 14 3685.2006.10.1.3
figure 3: i fastcharge vs. r set . protection circuitry over-voltage protection an over-voltage event is defined as a condition where the voltage on the bat pin exceeds the maximum battery charge voltage and is set by the over-voltage protection threshold (v ovp ). if an over-voltage condition occurs, the aat3685 charge control will shut down the device until voltage on the bat pin drops below the over-voltage protec- tion threshold (v ovp ). the aat3685 will resume normal charging operation after the over-voltage condition is removed. during an over-voltage event, the stat leds will report a system fault; the actual fault condition may also be read via the data pin signal. over-temperature shutdown the aat3685 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 dis- play a system fault. after the system recovers from a temperature fault, the device will resume charging operation. the aat3685 checks battery temperature before starting the charge cycle, as well as during all stages of charging. this is accomplished by monitoring the voltage at the ts pin. this system is intended for use negative temperature coefficient (ntc) thermis- tors which are typically integrated into the battery package. most commonly used ntc thermistors used in battery packs are approximately 10k at room temperature (25c). the ts pin has been specifically designed to source 80 a of current to the thermistor. the voltage on the ts pin that results from the resistive load should stay within a window from 335mv to 2.32v. if the battery becomes too hot during charging due to an internal fault, the thermis- tor will heat up and reduce in value, thus pulling the ts pin voltage lower than the ts1 threshold, and the aat3685 will halt charging and signal the fault con- dition. if the use of the ts pin function is not required by the system, it should be terminated to ground using a 10k resistor. alternatively, on the aat3685-1, the ts pin may be left open. battery charge status indication the aat3685 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 aat3685 also provides a bi-directional data reporting function so that a system microcontroller may interrogate the data pin and read any one of 14 system states. status indicator display simple system charging status may be displayed using one or two leds in conjunction with the stat1 and stat2 pins on the aat3685. these two pins are simple switches to connect the display led cathodes to ground. it is not necessary to use both display leds if a user simply wants to have a single lamp to show "charging" or "not charging." this can be accomplished by just using the stat1 pin and a single led. using two leds and both stat pins simply gives the user more information for charging states. refer to table 2 for led dis- play definitions. aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 15 r set (k 10 100 1000 10000 1 10 100 1000 setl seth
the led anodes should be connected to v adp/usb . the leds should be biased with as little current as necessary to create reasonable illumination; there- fore, a ballast resistor should be placed between each of the led cathodes and the stat1/2 pins. led current consumption will add to the over-ther- mal power budget for the device package, hence it is recommended to keep the led drive current to a minimum. 2ma should be sufficient to drive most low-cost green, red, or multi-color leds. it is not recommended to exceed 8ma for driving an indi- vidual status led. the required ballast resistor value can be estimat- ed using the following formulas: eq. 2: example: note: red led forward voltage (v f ) is typically 2.0v @ 2ma. table 2 shows the four status led display conditions. digital charge status reporting the aat3685 has a comprehensive digital data reporting system by use of the data pin feature. this function can provide detailed information regarding the state of the charging system. the data pin is a bi-directional port which will read back a series of data pulses when the system microcontroller asserts a request pulse. this sin- gle strobe request protocol will invoke one of 14 possible return pulse counts in which the micro- controller can look up based on the serial report shown in table 3. the data pin function is active low and should nor- mally be pulled high to v adp/usb . 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 microcontroller. 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 tim- ing 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 the value of the pull-up resistor used is too high, the strobe pulse from the system microcontroller may 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 at the v usb input. if the data line is pulled high to a voltage level less than 5.0v, the pull-up resistor may be calculated based on a recommended minimum pull-up current of 3ma. use the following formula: eq. 3: aat3685 lithium-ion/polymer battery charger 16 3685.2006.10.1.3 table 2: led display status 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. v pull-up r pull-up 3ma (5.0v - 2.0 v) r b(stat1) = = 1.5k 2ma (v apd/usb - v f(led) ) r b(stat1/2) = i led(stat1/2)
aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 17 table 3: serial data report table. figure 4: data pin application circuit. n data report status 1 chip over-temperature shutdown 2 battery temperature fault 3 over-voltage turn off 4 not used 5 not used 6 not used 7 not used 8 not used 9 not used 10 not used 11 not used 12 not used 13 seth battery condition mode 14 seth charge reduction in constant current mode 15 seth constant current mode 16 seth constant voltage mode 17 seth end of charging 18 setl battery condition mode 19 setl charge end of charging reduction in constant current mode 20 setl constant current mode 21 setl constant voltage mode 22 setl end of charging 23 data report error aat3685 status control 1.8v to 5.0v data pin r pull_up p gpio port gpio in in out out
data timing the system microcontroller should assert an active low data request pulse for minimum duration of 200ns; this is specified by t lo(data) . upon sensing the rising edge of the end of the data request pulse, the aat3685 status data control will reply the data word back to the system microcontroller after a delay specified by the data report time specification t data(rpt) . the period of the following group of data pulses will be specified by the t d ata specification. aat3685 lithium-ion/polymer battery charger 18 3685.2006.10.1.3 timing diagram thermal considerations the aat3685 is packaged in a pb-free, 3x3mm tdfn package which can provide up to 2.0w of power dissipation when it is properly bonded to a printed circuit board and has a maximum thermal resistance of 50c/w. many considerations should be taken into account when designing the printed circuit board layout, as well as the placement of the charger ic package in proximity to other heat gen- erating devices in a given application design. the ambient temperature around the charger ic will also have an affect on the thermal limits of a bat- tery charging application. the maximum limits that can be expected for a given ambient condition can be estimated by the following discussion. first, the maximum power dissipation for a given situation should be calculated: eq. 4: where: p d = total power dissipation by the device v in = input voltage level, v adp/usb v bat = battery voltage as seen at the bat pin i cc = maximum constant fast charge current programmed for the application i op = quiescent current consumed by the charger ic for normal operation next, the maximum operating ambient temperature for a given application can be estimated based on the thermal resistance of the 3x3mm tdfn pack- age when sufficiently mounted to a pcb layout and the internal thermal loop temperature threshold. eq. 5: sq sq pulse 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 t a = t j - ( ja p d ) p d = [(v in - v bat ) i cc + (v in i op )]
where: t a = ambient temperature in degrees c t j = maximum device junction temperature protected by the thermal limit control p d = total power dissipation by the device ja = package thermal resistance in c/w example: for an application where the fast charge current is set to 500ma, v usb = 5.0v and the worst case bat- tery voltage at 3.0v, what is the maximum ambient temperature at which the thermal limiting will become active? given: v usb = 5.0v v bat = 3.0v i cc = 500ma i op = 0.75ma t j = 140c ja = 50c/w using equation 4, calculate the device power dissi- pation for the stated condition: eq. 6: the maximum ambient temperature before the aat3685 thermal limit protection will shut down charging can now be calculated using equation 5: eq. 7: therefore, under the stated conditions for this worst case power dissipation example, the aat3685 will suspend charging operations when the ambient operating temperature rises above 89.81c. capacitor selection input capacitor in general, it is good design practice to place a decoupling capacitor between the adp/usb pin and ground. an input capacitor in the range of 1 f to 22 f 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 aat3685 input is to be used in a system with an external power supply source rather than a usb port v bus , such as a typical ac-to-dc wall adapter, then a c in capacitor in the range of 10 f should be used. a larger input capacitor in this application will minimize switching or power bounce effects when the power supply is "hot plugged" in. likewise, a 10 f or greater input capacitor is recommended for the usb input to help buffer the effects of usb source power switching noise and input cable impedance. output capacitor the aat3685 only requires a 1 f ceramic capaci- tor on the bat pin to maintain circuit stability. this value should be increased to 10 f or more if the battery connection is made any distance from the charger output. if the aat3685 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 10 f may be required to prevent the device from cycling on and off when no battery is present. printed circuit board layout considerations for the best results, it is recommended to physi- cally place the battery pack as close as possible to the aat3685 bat pin. to minimize voltage drops on the pcb, keep the high current carrying traces adequately wide. for maximum power dis- sipation of the aat3685 3x3mm tdfn package, the metal substrate should be solder bonded to the board. it is also recommended to maximize the substrate contact to the pcb ground plane layer to further increase local heat dissipation. refer to the aat3685 evaluation board for a good layout example (see figures 5 and 6). aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 19 t a = 140 c - ( 50 c/w 1.00375w) = 89.81 c p d = (5.0v - 3.0v) (500ma) + (5.0v 0.75ma) = 1.00375w
aat3685 evaluation board layout figure 5: aat3685 evaluation board figure 6: aat3685 evaluation board component side layout. solder side layout. aat3685 lithium-ion/polymer battery charger 20 3685.2006.10.1.3
aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 21 aat3685 evaluation board schematic diagram grn led d2 red led d1 8.06k r8 1.5k r5 1.5k r6 1.5k r9 open r3 10k r4 40.2k r7 10 f c1 1 2 3 pwrsel j2 sw1 lo hi dat a 1 2 3 on/off j1 adp/usb 1 bat 2 gnd 3 chr 4 en 5 ts 6 data 7 stat2 8 stat1 9 pwrsel 10 setl 11 seth 12 aat3685 u1 1 2 tb1 bat gnd ts a dp/usb a dp/usb gnd tdfn33-12 1 2 3 4 5 mini-b 10 f c2 gnd id d+ d- 1 2 3 tb2 open r2 open r1
aat3685 lithium-ion/polymer battery charger 22 3685.2006.10.1.3 22 3685.2006.10.1.3 aat3685 evaluation board bill of materials (bom) quantity description desig. footprint manufacturer part number 1 test pin data pad mill-max 6821-0-0001-00-00-08-0 1 connecting terminal block, usb,gnd tblok2 phoenix contact 277-1274-nd 2.54mm, 2 pos 1 connecting terminal block, bat, gnd, ts tblok3 phoenix contact 277-1273-nd 2.54mm, 3 pos 1 usb 2.0 receptacle, 5 pos usb usb-mini-b hirose electronic h2959ct-nd co. ltd. 2 capacitor, ceramic, 10 f c1, c2 0805 murata 490-1717-1-nd 6.3v 10% x5r 0805 1 typical red led, super d1 1206led chicago miniature cmd15-21src/tr8 bright lamp 1 typical green led d2 1206led chicago miniature cmd15-21vgc/tr8 lamp 2 header, 3-pin j1, j2 header2mm-3 sullins 6821-0-0001-00-00-08-0 1 resistor, 10k 1/16w 5% r4 0603 panasonic/ecg p10kcfct-nd 0603 smd 3 resistor, 1.5k 1/16w r5, r6, r9 0603 panasonic/ecg p1.5kcgct-nd 1% 0603 smd 1 resistor, 40.2k 1/16w r7 0603 panasonic/ecg p40.2khtr-nd 1% 0603 smd 1 resistor, 8.06k 1/16w r8 0603 panasonic/ecg p8.06khct-nd 1% 0603 smd 1 switch tact 6mm spst sw1 switch itt industries/ ckn9012-nd h = 5.0mm c&k div. 1 aat3685 lithium-ion/ u1 tdfn33-12 analogictech aat3685iwp polymer battery charger
ordering information package information all dimensions in millimeters. package marking 1 part number (tape and reel) 2 tdfn33-12 rnxyy aat3685iwp-4.2-t1 tdfn33-12 tmxyy aat3685iwp-4.2-1-t1 aat3685 lithium-ion/polymer battery charger 3685.2006.10.1.3 23 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737-4600 fax (408) 737-4611 ? 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. top view bottom view detail "b" detail "a" side view 3.00 2.40 + 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.

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