tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a lithium-ion battery charger features low power dissipation shutdown current: 1 a (typical) space-saving 8-pin msop package no inductor required 1% overall system accuracy charge current monitor output charge status indicator output foldback current limiting ?0 c to +85 c ambient operating temperature range typical applications pdas cradle chargers li-ion battery chargers desktop computers hand-held instruments cellular telephones battery operated devices self-charging battery packs general description the tc3827 is a battery charger controller for a single cell li-ion battery. using an external pmos transistor, safe and fast charging of a single li-ion cell is accomplished. features include over-current foldback, charge current monitor, and charge status led indicator output. an overall system accuracy of 1% ensures that the cell capacity is fully utilized without cycle life degradation. an external resistor sets charge current. the tc3827 operates with an input voltage range from 4.5v to 5.5v. it is specified over the ambient operating temperature range of ?0 c to +85 c and is available in a space-saving 8-pin msop. ordering information temperature part no. package range tc3827-4.1vua 8-pin msop ?0 c to +85 c tc3827-4.2vua 8-pin msop ?0 c to +85 c 8-pin msop pin configuration gnd v drv v sns v in mode i mon v out shdn 1 2 3 4 8 7 6 5 tc3827 r sense ndp6020p pmos +5 v in v sns v drv gnd v in v out shdn imon mode led 10 f controller tc3827 li-ion 22 f + shdn mode imon functional block diagram typical application circuit e/a shdn v out gnd v v in v sns v ref + e/a + c/a + control block k i mon mode tc3827 drv figure 1. tc3827 typical application circuit
2 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a absolute maximum ratings* input voltage (v in ), v out , v sns , mode, and i mon ........... .............................................................. ?.3v to 6.0v shdn ...............................................?.3v to (v in + 0.3v) 8-pin msop (derate 4.1mw/ c above +70 c) ..... 330mw operating ambient temperature range .. ?0 c to +85 c storage temperature range ................. ?5 c to +150 c lead temperature (soldering, 10 sec) ................. +300 c vapor phase (60 sec) ........................................... +210 c infrared (15 sec) .................................................... +220 c i imon (source) ......................................................0.375ma electrical characteristics: v in = [v reg + 1v] , t a = -20 c to +85 c, unless otherwise noted. typical values at t a = +25 c, r sense = 500m ? , test circuit figure 3. symbol parameter test conditions min typ max units i vin power supply current shutdown mode, v shdn = 0v 1 15 a constant voltage mode 350 560 v in power supply voltage in 4.5 5.5 v voltage regulation (constant voltage mode) v reg battery regulation volts 3827- 4.2vua 4.2 v 3827- 4.1vua 4.1 v out output voltage accuracy v in = v reg + 1v to 5.5v, 1 +1 % li reg line regulation v in = 4.5v to 5.5v, i out = 75ma ?0 +10 mv ld reg load regulation i out =10ma to 75ma ? 0.2 +1 mv id isch output reverse leakage v in = floating, v out = v reg ? 5 a mosfet gate drive i drv gate drive current sink, constant voltage mode (note 1) 1 ma source, constant voltage mode (note 1) 0.08 v drv gate drive min voltage 1.0 v current sense amp v gain gain ( ? v gs / ? v out ) 100 db v cs current limit threshold (v in ?v sns ) @ i max 40 53 75 mv i sc short circuit current 46 ma k kfactor 0.46 a/a mode v th mode threshold v reg ? v ol mode low voltage i sink = 10ma, v out = 3.5v 400 mv i lk mode leakage current v mode = 5.5v, i o = 0ma, +1 a mode = constant voltage shdn v ih shdn high threshold 40 %v dd v il shdn low threshold 25 %v dd i lk shdn leakage current v shdn = 0v to 5v +1 a i mon ? v imon current sense gain v o = 0v to 3.5v,r l > 20k ? 26 v/v ? (v in - v sns ) i mode (sink) .............................................................. 20ma i drv ............................................................................1ma esd rating ................................................................. 2kv *static-sensitive device. unused devices must be stored in conductive material. protect devices from static discharge and static fields. stresses above those listed under absolute maximum ratings may cause perma- nent damage to the device. these are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. notes: 1. where v out = 1% from nominal, continuous current.
3 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a pin no. 8-pin msop symbol type description 1 shdn signal input shutdown input 2 gnd power system ground 3 mode signal output charge mode indicator 4i mon voltage output buffered copy of current sense resistor drop 5v out voltage input charger dc output voltage sense 6v drv signal output gate drive to external mosfet 7v sns signal input current sense voltage input 8v in power charger dc input voltage pin description functional description the tc3827 controller only requires a p-channel power mosfet and two small capacitors to perform as an inex- pensive li-ion battery charger. the tc3827 controller drives an external pmos to provide a regulated output current to charge the battery. initially, current limited charging occurs until a pre-specified battery voltage is measured at the v out pin. it then switches to constant-voltage mode. during constant-voltage mode the tc3827 works like a linear regulator, holding the output voltage within the specified accuracy. the charger output is sensed at the v out pin. the charging current follows the foldback characteristic as shown in figure 2. the sense resistor sets the maximum charging current, i max . the voltage drop across the current sense resistor is sensed at the v sns input. an amplified copy of this sense voltage is provided as output on the current monitor pin (i mon ). when the battery is deeply discharged to a minimum voltage level, or if the battery is shorted, the current sense circuit folds back the charge current to limit the power dissipation of the pmos. both the v in and v out pins i/o description shdn: when shdn is low, v drv is pulled high to v in and the charge is interrupted. gnd: connect to the battery? negative terminal. see layout guidelines for information on system grounding. v out : battery positive terminal and charger regulated output voltage.this pin is connected to the external pmos drain and directly to the load for optimal regulation. v out pin draws typically 1 a from the battery when v in power is removed. requires a bypass capacitor. mode: charge status indicator. mode is an open-drain, n-channel mosfet capable of sinking 20ma for an led status indication of charger in current limited mode. led is off in current-voltage mode. v drv : gate drive output for the external pmos pass device. i mon : battery charge current profile. this output is an amplified copy of the voltage drop across the current sense resistor . it can be used as input to an a/d converter to provide the controller with information about the charge current profile. v in : charger power supply input (+6v absolute max.). bypass to gnd with a capacitor. v sns : battery charge current sense voltage feedback. this voltage is developed across a small value precision resistor that is in series with the battery. of the ic need a suitable bypass capacitor. the tc3827 also has a logic-level shutdown input, shdn, which may be connected to the input voltage to enable the ic. pulling it ?ow?or to ground will disable the pmos drive (v drv pulled up to v in voltage). also, a charger mode pin (mode) is provided to drive an optional led for a visual indication of current limited mode operation. led will be turned off in constant voltage mode operation.
4 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a applications information a typical li-ion cell should be charged at a controlled current until it reaches 4.1v or 4.2v (depending on the type of cell), then charged at this voltage. the tc3827 is de- signed to offer the maximum integration and function with a small application circuit. the only necessary external com- ponents are a pmos , two small capacitors, and an r sense . the charge current profile can be monitored using the voltage signal at i mon . the use of an led as a status indicator is optional. the application circuit is shown in figure 1. selecting external components power supply input in most applications, this will be a small ?all cube switching converter with an output voltage limit range of 5v to 6v. p-channel pass device the pmos is used to regulate current from the source into the li-ion cell. specifications to consider when choosing an appropriate pmos are the minimum drain-source break- down voltage, the minimum turn-on threshold voltage (v gsth ), drain current and power-dissipation capabilities. bypass capacitors bypass v in with a capacitor value of at least 10 f. bypass v out with a capacitor value of at least 1 f. charger modes description initiating a charge cycle the tc3827 initiates a charge upon toggling the shut- down pin high, insertion of the battery or application of an external power source. the tc3827 provides a foldback current limited charge where an external current sense resistor sets i max . the voltage drop across the current sense resistor is applied to the v in -v sns pins and presented to the current limited control-loop.the current loop will protect a deeply discharged (or shorted) battery by folding back the current limited charge, and reduces the power dissipation in pmos. current limited, constant-voltage charge cycle the tc3827 begins to charge the li-ion cell by turning on the external pmos. the charge continues until the battery voltage rises to the lithium-ion cell voltage of 4.2v or 4.1v (depending on type of cell). as the battery voltage reaches the regulated output voltage, the internal feedback figure 3. tc3827 test circuit v reg v out i reg i max i foldback constant voltage mode foldback current limited mode i sc i out figure 2. tc3827 charging characteristic r sense =500m ? s g d ndp6020p pmos v sns v drv gnd v in v in v out v out shdn i mon mode 10 f tc3827 22 f
5 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a control loop changes from current limiting to voltage regula- tion. if an external micro-controller determines battery con- ditions are unsafe for charge it can toggle the shutdown pin low and interrupt the charge cycle. otherwise, once the pre- determined cell voltage is reached the tc3827 shifts into a constant-voltage mode (linear regulation) and a variable charge current is applied as required to maintain the battery cell voltage to within 1% accuracy of the cell voltage set- point. i mon charge current status the i mon pin provides an output voltage that is propor- tional to the battery charging current . it is an amplified version of the sense resistor voltage drop that the current loop uses to control the pmos device. this voltage signal can be applied to the input of an a/d converter and used by a controller to display information about the state of the battery or charge current profile. mode charge mode status led the mode pin indicates the battery charging mode. an led can be connected to the mode for a visible indicator. alternatively, a pull-up resistor (typically 100k ? ) from the interfacing logic supply to mode provides a logic-level output. the mode pin will toggle low and the led will illuminate when the charger is in the current limited mode. the mode pin toggles to a high impedance state and the led will be off during constant-voltage mode charging or if the battery is not connected. the mode pin toggles at a v out of v reg , typically. application circuit design due to the low efficiency of linear regulator charging, the most important factors are thermal design and cost, which is a direct function of the input voltage, output current and thermal impedance between the pmos and the ambi- ent cooling air. the worst-case situation is when the battery is shorted since the pmos has to dissipate the maximum power. a tradeoff must be made between the charge cur- rent, cost and thermal requirements of the charger. higher current requires a larger pmos with more effective heat dissipation leading to a more expensive design. lowering the charge current reduces cost by lowering the size of the pmos, possibly allowing a smaller package such as 6-pin sot. the following designs consider both options. higher current option the current sense resistor for the circuit shown in figure 1 is calculated by: r sense = v cs /i max . where v cs is the current limit threshold voltage of 40mv to 75mv, 50mv typical. if i max = 1a is desired, r sense = 50m ?. pre-regulated input voltage (5v 0%) for this application, the required ja thermal imped- ance is calculated as follows: if: the pmos data sheet allows a max junction temperature of t jmax = 150 c , then: at 50 c ambient with convection cooling, the maximum allowed junction temperature rise is: t jmax ?t amax = 150 c ?50 c = 100 c. ja = ? t/(i o x k x v in ) = 100/(1 x 0.46 x 5.5) = 39.5 c/w this k factor is : k = i sc /i max 0.46. this thermal impedance can be realized using the transistor shown in figure 1 when mouted to a heat sink. the sa or thermal impedance of a suitable heatsink is calculated below: sa ( ja ? jc ? cs ) = 39.5 ?2.5 ?0.3 = 36.7 c/w where the jc , or junction-to-case thermal impedance is for the pmos from the pmos data sheet. a low cost heatsink is thermalloy type pf430, with a sa = +25.3 c/w.
6 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a lower current option preregulated input voltage (5v +/- 10%) if lower charging current is allowed, the ja value can be increased, and the system cost decreased. this is accom- plished by using a fdc638p pmos, for example, in a 6-pin sot package mounted on a small 1in x 1in area of 2oz cu on fr-4 board. this provides a convection cooled thermal impedance of ja = +78 c/w. allowing a maximum fet junction temperature of +150 c, at +50 c ambient, with convection cooling the maximum allowed heat rise is: 150 c?0 c = 100 c. the maximum short circuit current, i sc, is found as: i sc = ? t/( ja x v in ) = 100/(78 x 5.5) = 0.23a thus the maximum charging current, i max , is: i max = i sc /k = 0.51a the current sense resistor for this application is then: r sense = v cs /i max = 0.05/0.51 = 98m ? 100m ? fet selection the type and size of the pass transistor is determined by the threshold voltage, input-output voltage differential and load current. the selected pmos must satisfy the physical and thermal design requirements. to ensure that the maxi- mum v gs provided by the controller will turn on the fet at worst case conditions, (i.e., temperature and manufacturing tolerances) the maximum available v gs must be deter- mined. maximum v gs is calculated as follows: v gsmax = v in ?(i max x r sense ) ?v drvmax for example: v in = 5v, and i max = 1a, v gsmax = 5v - (1a x 50m ?) ?1v= 3.95v the difference between v in and v o (v ds ) must exceed the voltage drop due to the sense resistor plus the on- resistance of the pmos at the maximum charge current. v ds v in ?v o ?v cs = 5v ?4.2v ?0.075v = 0.725v the maximum r ds(on) required at the available gate drive (v dr ) and drain-to-source voltage (v ds ) is: r ds(on) = v ds /i max 0.725v/1a = 725m ? the selected pmos must satisfy these criteria. external capacitors the tc3827 is stable with or without a battery load, and virtually any good quality output filter capacitors can be used, independent of the capacitor? minimum esr (effec- tive series resistance) value. the actual value of the capacitor and its associated esr depends on the g m and capacitance of the external pmos device. a 22 f tantalum or aluminum electrolytic capacitor at the output is sufficient to ensure stability for up to a 10a output current. shutdown mode applying a logic high signal to the shdn pin or tying it to the input pin will enable the output. pulling this pin low or tying it to ground will disable the output. in shutdown mode, the controller? quiescent current is reduced to typically 1 a. short circuit protection the pmos is protected during short circuit conditions with a foldback type of current limiting that reduces the power dissipation. current sense resistor the current limit sense resistor, r sense , is calculated previously. proper de-rating is advised to select the power dissipation rating of the resistor. the simplest and cheapest sense resistor for high current applications, is a pcb trace. however, the temperature dependence of the copper trace and the thickness tolerances of the trace must be consid- ered in the design. copper? tempco, in conjunction with the proportional- to-absolute temperature ( 0.3%) current limit voltage, can provide an accurate current limit. alternately, an appropriate sense resistor, such as surface mount sense resistors, available from krl, can be used. pcb layout issues for optimum voltage regulation, place the load as close as possible to the device? v out and gnd pins. it is recommended to use dedicated pcb traces to connect the pmos drain to the positive terminal and v ss to the negative terminal of the load to avoid voltage drops along the high current carrying pcb traces. if the pcb layout is used as a heatsink, adding many vias around the power fet helps conduct more heat from the fet to the back-plane of the pcb, thus reducing the maximum fet junction temperature.
7 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a v out vs i load (v in =5.1v) 4.090 4.095 4.100 4.105 4.110 0 200 400 600 800 1000 i load - ma v out vs v in (i load =1a) 4.090 4.095 4.100 4.105 4.110 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 v in - v figure. 4 figure. 5 v out vs v in (i load =10ma) 4.090 4.095 4.100 4.105 4.110 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 v in - v figure. 6 i gnd vs v in (i load =10ma) 0.200 0.210 0.220 0.230 0.240 0.250 0.260 0.270 0.280 0.290 0.300 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 v in - v figure. 7 typical curves v out - v v out - v i gnd - ma v out - v i gnd vs v in (i load =1a) 0.200 0.250 0.300 0.350 0.400 0.450 0.500 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 v in - v figure. 8 i gnd vs i load (v in = 5.1v) 0.000 0.100 0.200 0.300 0.400 0.500 0.001 0.01 0.1 1 10 100 1000 i load - ma figure. 9 i gnd - ma i gnd - ma
8 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a figure. 14 v out vs temperature (v in = 5.1v, i load = 10ma) 4.080 4.100 4.120 4.140 4.160 4.180 4.200 4.220 -20.0 0.0 20.0 40.0 60.0 80.0 temperature - c v out = v out figure. 13 current limit foldback (vin = 5.1v, r sense =0.5ohms) 0.000 1.000 2.000 3.000 4.000 5.000 0 20 40 60 80 100 120 i load -ma figure. 12 typical curves (cont.) v out - v v out - v i gnd vs temperature (v in = 5.1v, i load = 10ma) 0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.450 0.500 -20.0 0.0 20.0 40.0 60.0 80.0 temperature - c figure. 10 power-up/power-down (i load =10ma) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0.0 1.0 2.0 3.0 4.0 5.0 4.0 3.0 2.0 1.0 0.0 v in - v figure. 11 i gnd - ma v out - v line transient response (10 f output cap) v out - v 5.5 4.5 4.2 4.1 4.0 v out - v
9 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a printed in the u.s.a. package dimensions dimensions: inches (mm) 8-pin msop .122 (3.10) .114 (2.90) .122 (3.10) .114 (2.90) .043 (1.10) max. .006 (0.15) .002 (0.05) .016 (0.40) .010 (0.25) .197 (5.00) .187 (4.80) .008 (0.20) .005 (0.13) .028 (0.70) .016 (0.40) 6 max. .026 (0.65) typ. pin 1 taping form pin 1 pin 1 component taping orientation for 8-pin msop devices user direction of feed user direction of feed standard reel component orientation for tr suffix device reverse reel component orientation for rt suffix device w p package carrier width (w) pitch (p) part per full reel reel size 8-pin msop 12 mm 8 mm 2500 13 in carrier tape, number of components per reel and reel size
10 lithium-ion battery charger tc3827 tc3827-2 12/12/00 ?2001 microchip technology inc. ds21558a information contained in this publication regarding device applications and the like is intended through suggestion only and ma y be superseded by updates. it is your responsibility to ensure that your application meets with your specifications. no representation or warrant y is given and no liability is assumed by microchip technology incorporated with respect to the accuracy or use of such information, or infringement of patent s or other intellectual property rights arising from such use or otherwise. use of microchip?s products as critical components in life support systems is not authori zed except with express written approval by microchip. no licenses are conveyed, implicitly or otherwise, except as maybe explicitly expressed herein, under any intellec- tual property rights. the microchip logo and name are registered trademarks of microchip technology inc. in the u.s.a. and othe r countries. all rights reserved. all other trademarks mentioned herein are the property of their respective companies. all rights reserved. ? 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