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general description the max2003/max2003a are fast-charge battery charg- ers (with conditioning) for nicd (nickel cadmium) or nimh (nickel-metal hydride) rechargeable batteries. the max2003a has the same features as the max2003 with an additional pulsed trickle-charge mode to prevent den- drite formation in nimh batteries. each can be config- ured as a switch-mode current regulator or as a gating controller for an external current source. switch-mode current regulation provides efficient energy transfer, reducing power dissipation and the associated heating. gating control of an external current source requires minimal components, saving space and cost. on-chip algorithms determine charge termination, so the max2003/max2003a can be used as stand-alone chargers. fast-charge termination is accomplished by five methods: temperature slope, negative voltage change, maximum temperature, maximum time, and maximum voltage. as a safety feature, the start of fast- charge is inhibited until battery voltage and temperature are within safe limits. by selecting the appropriate charge-termination method, a single circuit can be built with the max2003/max2003a to fast-charge both nimh and nicd batteries. the max2003/max2003a provide a switch-activated discharge-before-charge option that allows for battery conditioning and more accurate capacity measure- ment. other features include optional top-off charging and direct drivers for led status lights. the max2003, in dip and wide so packages, is a direct plug-in replacement for the bq2003. the max2003/ max2003a also come in a space-saving narrow so package. the max2003a evaluation kit (max2003a evkit-so) is available to assist in designs. ________________________applications battery-powered equipment: laptop, notebook, and palmtop computers handy-terminals portable consumer products: portable stereos cordless phones backup-battery applications: memory hold-up emergency switchovers ____________________________features ? stand-alone nicd or nimh fast chargers ? new pulsed trickle-charge mode (max2003a only) ? provide switch-mode, gated, or linear control regulation ? small, narrow so package available ? on-chip fast-charge termination methods: temperature slope maximum voltage negative delta voltage maximum time maximum temperature ? automatically switch from fast-charge to trickle-charge or top-off charge ? optional discharge-before-charge ? directly drive status leds ? optional top-off charge max2003/max2003a nicd/nimh battery fast-charge controllers ________________________________________________________________ maxim integrated products 1 19-0371; rev 4; 5/97 part max2003 cpe max2003cse 0? to +70? 0? to +70? temp. range pin-package 16 plastic dip 16 narrow so ___________________pin configuration 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 v cc dis mod chg tm1 dven dcmd ccmd top view max2003 max2003a temp mcv tco sns v ss bat ts tm2 dip/so max2003cwe max2003c/d 0? to +70? 0? to +70? 16 wide so dice* * contact factory for dice specifications. evaluation kit manual follows data sheet max2003a cpe max2003acse max2003acwe max2003ac/d 0? to +70? 0? to +70? 16 plastic dip 16 narrow so 0? to +70? 0? to +70? 16 wide so dice* ordering information for free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. for small orders, phone 1-800-835-8769.
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = 4.5v to 5.5v, figure 1, all measurements are with respect to v ss , t a = t min to t max , unless otherwise noted.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. all pins to v ss ........................................................... -0.3v, +6.0v continuous power dissipation (t a = +70 c) plastic dip (derate 10.53mw/ c above +70 c) ........... 842mw narrow so (derate 8.70mw/ c above +70 c) ............. 696mw wide so (derate 9.52mw/ c above +70 c) ................. 762mw operating temperature range ............................... 0 c to +70 c storage temperature range ............................. -65 c to +150 c lead temperature (soldering, 10sec) ............................. +300 c v bat - v sns no load v cc = 5v v cc = 5v, v tco = 1.4v v cc = 5v v cc = 5v v cc = 5v v cc = 5v v ts - v sns v cc = 5v v cc = 5v conditions mv 16 v therm thermistor input resolution (note 2) mv 12 - ? v negative delta voltage (note 2) mv 30 v snshi - v snslo delta sense voltage (note 1) v 0.044v cc 0.044v cc - 25mv 0.044v cc + 25mv v snslo sense trip threshold low v 0.05v cc 0.05v cc - 25mv 0.05v cc + 25mv v snshi sense trip threshold high v 0.0 v cc v cell cell potential ma 0.75 2.2 i cc v 4.5 5.0 5.5 v cc supply voltage supply current v (v ltf /8) (v ltf /8) (v ltf /8) + (7v tco /8) + 7v tco /8 + (7v tco /8) - 30mv + 30mv v htf high-temperature trip threshold v v ltf - 0.2v cc v ltf v tco temperature cutoff voltage v 0.4v cc 0.4v cc - 30mv 0.4v cc + 30mv v ltf low-temperature trip threshold v v edv v edv + 0.2v cc v mcv maximum cell voltage v 0.0 v cc v bat battery voltage input v 0.0 v cc v temp temperature potential v 0.0 v cc v ts temperature sense input voltage units min typ max symbol parameter v cc = 5v v 0.2v cc 0.2v cc - 30mv 0.2v cc + 30mv v edv end-of-discharge voltage
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = 4.5v to 5.5v, figure 1, all measurements are with respect to v ss , t a = t min to t max , unless otherwise noted.) timing characteristics (v cc = 4.5v to 5.5v, figure 1, all measurements are with respect to v ss , t a = t min to t max , unless otherwise noted. typical values are at v cc = 5.0v, t a = +25 c.) note 3: ratio of actual versus expected timeout (see table 4). tested with tm1 = tm2 = floating. note 4: to recognize a battery insert signal, v bat must be greater than v mcv for at least t bto . mod pin in fast-charge mode, v cc = 5v (note 3) ccmd, dcmd conditions khz 100 f max mod switching frequency 0.84 1.00 1.16 s 1.0 t mpw minimum pulse width variation of fast-charge timeout units min typ max symbol parameter ccmd, dcmd, dven at v cc and v ss ccmd, dcmd, dven ccmd, dcmd, dven tm1, tm2 = v cc tm1, tm2 = v ss for dis, temp and chg, 0ma i load 5ma; for mod, 0ma i load 10ma a -1.0 1.0 i lkg input logic leakage 1.0 v cc - 1.0 v ih input logic voltage high a -70.0 i ih input logic current high a 70.0 i il input logic current low v v cc - 0.5 v oh logic-high threshold tm1, tm2 = tri-state bat, mcv, tco, sns, ts a -2.0 2.0 i iz input logic current high-z m 50 input impedance tm1, tm2 v v cc - 0.3 tm1, tm2 v 0.3 v il input logic voltage low ms 200 250 300 t bto battery replacement timeout (note 4) note 1: the sense trip levels are determined by an internal resistor divider network that provides a typical difference of 30mv from snshi to snslo. slight variation in this delta is seen if there is a resistor mismatch in the network. note 2: typical variations of negative delta voltage and thermistor input resolution parameters are less than 4mv. for dis, temp and chg, 0ma i load 5ma; for mod, 0ma i load 10ma v 0.5 v ol logic-low threshold conditions units min typ max symbol parameter
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers 4 _______________________________________________________________________________________ ______________________________________________________________ pin description name function 1 ccmd charge-enabled mode input?nitiates fast-charge on a digital signal (see detailed description for operating conditions). 2 dcmd discharge-enable mode input?nitiates discharge-before-charge on a digital signal (see detailed description for operating conditions). pin 3 dven negative delta voltage (- ? v) enable input?nables - ? v charge-termination mode. if dven is high, the con - troller uses negative-voltage change detection to terminate charge. if dven is low, this mode is disabled. 4, 5 tm1, tm2 these inputs are used to program the fast-charge and hold-off times, and to enable the top-off charge mode. the inputs can be high, low, or floating. see table 4 for details. 9 sns current-sense input?onnected to the negative battery terminal. ts and bat are referenced to this pin. the voltage at sns is directly proportional to the current through the battery and is used to determine how and when mod switches. 8 v ss ground 7 bat input voltage of single battery cell. if more than one cell is present, a resistor divider is needed to divide the voltage down to a single cell voltage. 6 ts temperature sense-voltage input from external thermistor. the thermistor temperature coefficient is nega - tive, so the higher the temperature, the lower the voltage at this pin (see detailed description for conditions of operation). 14 mod modulation output. this push/pull output switches to enable or disable charging current. if mod is high, current is enabled. if it is low, current is disabled. for a 5v supply, if the voltage at the sns pin is less than 220mv, mod is high. if the voltage is above 250mv, mod is low. 13 chg charge status output. this push/pull led driver indicates charge status (see detailed description ). 12 temp temperature status output. this push/pull led driver indicates that the temperature is outside the accept - able limits, and fast-charge and top-off are inhibited (see maximum temperature termination section in detailed description ). 11 mcv maximum cell voltage input. if the voltage from bat to sns exceeds the voltage at mcv, fast or top-off charging is terminated. 10 tco temperature cutoff-voltage input. if the voltage from ts to sns is less than the voltage at tco, a hot ther - mistor (negative coefficient) is detected and fast or top-off charging is terminated. 16 v cc power-supply voltage input (+5v nominal). bypass with a 0.1 f capacitor placed close to the device. 15 dis discharge-switch control output. this push/pull output turns on the fet that discharges the battery.
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers _______________________________________________________________________________________ 5 max2003 max2003a mod 5 r1 60.4k 1k 100k 1k r2 3.48k r3 33.2k 14 14 16 13v/2a dc source r tr 10k (*150 w (2w)) *trickle-charge rate c/40 1n5822 1n5822 0.1 m f 15 6 9 7 7 1, 3, 5 2, 4, 6 10v zener q1 p mmdf3p03hd 100 m h 1n5819 d s r b1 100k r b2 20k r sns 0.14 w 1% (1w) g 1700mah 6 nimh r dis 4 w (20w) ntc r t 100k r b 100k discharge rate 1c charge rate 1c c t 0.1 m f 1 m f 10k c b 0.1 m f d g s to v cc r t1 r t2 duracell dr17 q2 n mmsf5no3hd * component used for max2003. 8, 10, 12 9, 11, 13 4 2 1 3 12 13 11 10 dis ts sns bat v ss v cc v cc v cc tm2 push to discharge tm1 dcmd temp chg mcv tc0 led led ccmd dven 8 74hc04 lm317 243 w 22 m f 22 m f 22 m f 732 w adj 5v out in 0.1 m f 0.1 m f figure 1. switched-mode operation for nimh batteries with ? t/ ? t termination
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers 6 _______________________________________________________________________________________ detailed description the max2003/max2003a is a fast-charge battery charg - er that uses several methods of charge termination. the device constantly monitors your choice of the following conditions to determine termination of fast-charge: negative delta voltage (- ? v) rate-of-change of temperature ( ? t/ ? t) maximum voltage maximum time maximum temperature figure 2 shows the block diagram for the max2003/ max2003a. the first step in creating a fast-charge battery-charger circuit is to determine what type of battery will be used and what conditions the battery manufacturer recom - mends for termination of fast-charge. the type of bat - tery (nicd or nimh) and charge rate determine which method(s) of termination should be used. the charging characteristics of nimh batteries are simi - lar to those of nicd batteries, but there are some key dif - ferences that affect the choice of charge-termination method. since the type of charge termination can be dif - ferent for nicd and nimh batteries, it may not always be possible to use the same circuit for both battery types. a comparison of the voltage profiles for nicd and nimh batteries (shown in figure 3) reveals that nicd batteries display a larger negative drop in voltage at the end of charge than do nimh batteries. therefore, the negative delta voltage detection (- ? v) method of terminating fast-charge should only be used for nicd batteries. this termination method can cause errors in nimh bat - teries, since the drop in voltage at full capacity is not as great, and may lead to an overcharged battery. figure 4 shows the temperature profiles of the two types of batteries. during the first 80% of the charge cycle, the nicd battery temperature slowly rises. the nimh battery temperature rises more rapidly during this period. as the cells approach 90% of capacity, the temperature of the nicd cells rises more rapidly. when the cells approach full capacity, the rates-of-rise of temperature are comparable for both battery types. the rate of temperature change ( ? t/ ? t) can therefore be used to terminate fast-charge for both nicd and nimh batteries; fast-charge is terminated when the rate of temperature rise exceeds a preset rate. table 1 provides some guidelines to help in the selec - tion of the proper fast-charge termination method, but the manufacturer? recommendations take priority in case of conflict. figure 1 shows a standard application circuit for a switched-mode battery charger that charges nimh bat - teries at a rate of c. though this circuit is shown for nimh batteries, it can be used for nicd batteries (see table 1b). the description below will use this standard application to explain, in detail, the functionality of the max2003/max2003a. battery sense voltage the bat pin measures the per-cell voltage of the bat - tery pack; this voltage is used to determine fast-charge initiation and termination. the voltage is determined by the resistor-divider combination r b1 and r b2 , shown in figure 1, where: total number of cells = (r b1 / r b2 ) + 1 since bat has extremely high input impedance (50m minimum), reasonable values can be selected for resis - tors r b1 and r b2 . these values, however, must not be low enough to drain the battery or high enough to unduly lengthen the time constant of the signal going to the bat pin. the total resistance value from the positive to negative terminal of the battery (r b1 + r b2 ) should be between 100k and 500k to prevent these prob - lems. a simple rc lowpass filter (r b , c b ) may be needed to give a more accurate reading by removing any noise that may be present. remember that the rc time delay from the cell to bat must not exceed 200ms or the bat - tery detection logic might not function properly (r b x c b < 200ms). table 1a. fast-charge termination methods for nimh batteries table 1b. fast-charge termination methods for nicd batteries yes max temp. yes max time yes max voltage charge rate no yes >c/2 negative ? v ? t/ ? t yes max temp. yes max time yes max voltage charge rate yes yes >2c negative ? v ? t/ ? t 2c to c/2 * * yes yes yes * use one or both of these termination methods.
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers _______________________________________________________________________________________ 7 max2003 max2003a charge control state machine a/d discharge control display control temp chg ccmd dcmd dven timing control ltf check tco check osc tm1 tm2 v cc dis mod v ss mod control edv check mcv check (v ts - v sns ) tco ts sns bat mcv (v bat - v sns ) s s + + figure 2. block diagram 0.8 0 120 1.0 1.6 1.8 2.0 max2003-03 charge capacity (% of maximum) voltage/cell (v) 40 60 20 80 100 1.4 1.2 nicd nimh figure 3. voltage-charge characteristics of nicd and nimh batteries 15 0 120 20 25 40 50 45 55 max2003-04 charge capacity (% of maximum) temperature (?) 40 60 20 80 100 35 30 nicd nimh figure 4. temperature-charge characteristics of nicd and nimh batteries
max2003/max2003a temperature measurement the max2003/max2003a employs a negative tempera - ture-coefficient (ntc) thermistor to measure the bat - tery? temperature. this temperature value can be used to determine start and termination of fast-charge. the two temperature conditions that can be used for fast- charge termination are: maximum temperature rate-of-change of temperature ( ? t/ ? t) figure 5 shows the various temperature cutoff points and the typical voltages that the device will see at the ts pin. v ltf (low-temperature fault voltage) refers to the volt - age at ts when the battery temperature is too low, and v htf (high-temperature fault voltage) refers to the high- temperature cutoff. if the voltage is outside these limits, the max2003/max2003a will not enter fast-charge mode. after fast-charge is initiated, the termination point for high-temperature termination is v tco (temper - ature cutoff voltage), rather than v htf . see figure 5 for temp led status. v ltf is set internally at 0.4v cc , so (with a 5v supply) v ltf is 2v. v tco is set up using external resistors to determine the high-temperature cutoff after fast-charge begins. v htf is internally set to be (v ltf - v tco ) / 8 above v tco . thermistors are inherently nonlinear with respect to temperature. this nonlinearity is especially noticed when ? t/ ? t measurements are made to determine charge termination. the simplest way around this is to place a resistor-divider network in parallel with the ther - mistor (figure 6) to reduce the effects of nonlinearity. the lowpass filter (r t , c t ) placed on the ts pin attenu - ates high-frequency noise on the signal seen by ts. charge pending before fast-charge is initiated, the cell voltage and tem - perature of the battery pack must be within the assigned limits. if the voltage or temperature is outside these limits, the device is said to be in a ?harge-pend - ing?state. during this mode, the chg pin will cycle low (led on) for 0.125sec and high (led off) for 1.375sec. fast-charge is normally initiated if the cell voltage is greater than v edv (end-of-discharge voltage). if the cell voltage is too low (below v edv ), the device waits until the trickle current brings the voltage up before fast- charge is initiated. v edv is set internally at 0.2v cc , so (for a 5v supply) v edv is 1v. if the temperature of the cell is not between v ltf and v htf the device is also in a charge-pending state (see temperature measurement section). initiate fast-charge if the max2003/max2003a are out of the charge-pend - ing state, fast-charge can be initiated upon one of the following conditions: battery replacement applying power to the max2003/max2003a (battery already present) digital control signal during fast-charge, the chg pin will be continuously low (led on). for the initial period of fast-charge (the hold-off time), the voltage charge-termination methods are disabled. the hold-off time is a function of the charge rate selected by tm1 and tm2 (see table 4). nicd/nimh batter y fast-char ge contr ollers 8 _______________________________________________________________________________________ v cc = 5v v ltf - v tco v ltf = 0.4v cc 1 / 8 (v ltf - v tco ) 7 / 8 (v ltf - v tco ) v htf v tco v ss = 0v off on on temp led status figure 5. temperature measurement scale rc filter 100k r t v cc c t 0.1 m f ntc ts sns rt2 rt1 max2003 max2003a figure 6. thermistor configuration for temperature measurement
battery replacement before a battery is inserted, the bat pin is pulled high - er than the maximum cell voltage (mcv) by the resistor (r tr ) and the divider network (r b1 /r b2 ) (figure 1). when the battery is inserted, the voltage per cell at bat falls from the default voltage to the battery voltage. fast-charge is initiated on a falling edge when the bat voltage crosses the voltage on mcv. applying power to the max2003/max2003a (battery already present) there may be some cases where a battery is connect - ed before power is applied to the max2003/ max2003a. when power is applied, the device goes into reset mode for approximately 1.5sec and then samples the ccmd and dcmd pins. its charge status is determined by the voltage at both the ccmd and dcmd pins. table 2 summarizes the various conditions the max2003/max2003a might see on power-up. table 2 shows that the max2003/max2003a can be set-up for fast-charge on power-up by making sure ccmd and dcmd are at the same potential. if fast- charge on power-up is not desired, make sure ccmd and dcmd are at different logic levels during power- up, and use a digital signal to control fast-charge (see digital control section). digital control the ccmd pin can be used to initiate fast-charge. this is useful when neither the power supply nor the battery can be removed from the charger. the ccmd signal needed to initiate fast-charge depends on the potential at dcmd. if dcmd is low, a rising edge on ccmd initiates fast- charge. if dcmd is high, a falling edge on ccmd pro - vides the fast-charge signal. table 3 summarizes the conditions used to start fast-charge. discharge-before-charge (optional) the discharge-before-charge function is optional and can be used to condition old batteries. it is especially useful in nicd batteries, since it alleviates the voltage depression problems associated with partially dis - charged nicd cells. the discharge-before-charge function is initiated by a rising edge into dcmd. when the digital signal is applied, the dis pin will be pulled high, turning on the attached circuit and dis - charging its battery. the discharge process continues until the single cell voltage drops below 0.2v cc . during the discharge phase, the chg pin will be low (led on) for 1.375sec and high (led off) for 0.125sec. the max2003/max2003a does not control the current during discharge-before-charge. if the discharge rate is too great, the battery could overheat and be dam - aged. the battery manufacturer will be able to specify a safe discharge rate, but a rate of c or slower is typi - cally acceptable. it is also important to choose compo - nents (q2, r dis ) that are rated for that particular discharge rate. since the gate-source drive for q2 can be as low as 4.5v, use a logic-level mosfet. fast-charge current the fast-charge current can be generated using two categories of circuits: circuits with a sense resistor (r sns ) circuits without sense resistor (sns tied to v ss ) circuits with sns resistor the standard application circuit of figure 1 uses an inductor and a switched mode of operation to supply the current. the charge current is determined by the sense resistor placed between the negative terminal of the battery (sns) and ground (v ss ). the sns pin is the input to a comparator with hystere - sis. if the voltage at sns drops below 0.044v cc , the mod pin is turned on. if the sns voltage is above 0.050v cc , mod is turned off. in the switched mode of max2003/max2003a nicd/nimh batter y fast-char ge contr ollers _______________________________________________________________________________________ 9 table 2. device status on power-up if battery is already present table 3. digital control of fast-charge (v cc and battery present) the device does not enter fast-charge immediately. ? fast-charge is initiated by the rising edge of a pulse on ccmd. low high fast-charge is initiated on power-up. high high the device does not enter fast-charge immediately. fast-charge is initiated by the falling edge of a pulse on ccmd. high low ccmd fast-charge is initiated on power-up. low low max2003/max2003a status when power is applied dcmd fast-charge is initiated by a falling edge on ccmd. high ccmd fast-charge is initiated by a rising edge on ccmd. low ccmd status to initiate fast-charge dcmd
max2003/max2003a operation, the sns voltage ramps between 0.044v cc and 0.050v cc , which is 220mv and 250mv when v cc is 5v (figure 7). the average voltage at sns, therefore, is 235mv, and can be used to calculate the charge cur - rent as follows: i charge = 0.235v / r sns where r sns is the sense resistor and i charge is the charge current required. circuits without sns resistor in some applications (shown later), sns is tied directly to ground. in these cases, the mod pin remains on until any one charge-termination condition is exceeded (figure 8). a reasonable external current limit (such as a current-limited dc source) must be provided for these applications, to prevent battery damage due to excessive charge currents. charge termination the max2003 has several charge-termination methods. the termination method selected depends on the type of battery and charge rate used. table 1 summarizes the conditions used to terminate fast-charge with differ - ent battery types and charge rates. temperature rate termination the temperature rate termination ( ? t/ ? t) method ter - minates fast-charge when a particular rate-of-change in temperature is exceeded. as the battery begins fast- charge, its temperature increases at a slow rate. when the battery nears full capacity, this rate of temperature change increases. when the rate of temperature change exceeds a preset number, fast-charge is termi - nated. this method of fast-charge termination can be used for both nicd and nimh batteries. the max2003 samples the voltage at the ts pin every 34 seconds and compares it with a value taken 68 seconds earlier. since an ntc thermistor is used for temperature measurements, a gradual rise in temperature will result in successively lower voltage readings. if the new reading is more than 0.0032v cc (16mv for v cc = 5v) below the old reading, fast-charge is terminated. the max2003a varies the sampling interval as a function of charge rate (table 4). as the charge rate increases, the sampling interval decreases, thereby allowing more accurate termination of fast charge. note: this method of charge termination is valid only when the battery? temperature is between v ltf and v tco (figure 5). nicd/nimh batter y fast-char ge contr ollers 10 ______________________________________________________________________________________ time time time 0 0 0 mod sns i load 0.044 v cc 0.050 v cc v cc i bat fast charge fast-charge terminate figure 7. current regulation with an sns resistor time time sns = 0v time 0 0 mod sns i load 0.044 v cc 0.050 v cc v cc i bat fast charge fast-charge terminate figure 8. current regulation without an sns resistor
negative delta voltage termination the negative delta voltage termination (- ? v) method measures a negative delta voltage to determine termi - nation of fast-charge. after maximum charge is reached, the terminal voltage of nicd batteries declines significantly, whereas the terminal voltage of nimh batteries does not. hence, the - ? v method of fast-charge termination is suitable for nicd batteries, but not for nimh batteries. the max2003/max2003a sample the bat pin every 34 seconds and compare it with all previous values. if the new value is less than any of the previous values by more than 12mv, a negative delta voltage has been detected and fast-charge is terminated. note: this method of charge termination is valid only when the voltage at bat is between v mcv and v mcv - 0.2v cc . the - ? v method is inhibited during the hold-off time to prevent false termination of fast-charge. the hold-off time depends on the charge rate used, and is selected by the inputs tm1 and tm2 (as shown in table 4). after the hold-off time has expired, the device begins to monitor bat for a voltage drop. maximum temperature termination the maximum temperature termination method is used as a safety net to prevent problems, and should never be needed under normal operation of the charger. the maximum temperature that the battery can reach during fast-charge has a corresponding voltage?he tempera - ture cutoff voltage (v tco ), as seen in figure 5. this volt - age is set externally at the tco pin using a resistor divider from v cc . although rarely experienced, an excessively low temperature will also terminate fast- charge. the minimum temperature is the low tempera - ture fault (v ltf ). this value is internally set at 0.4v cc . when the thermistor exceeds these temperature limits, fast-charge is terminated. the thermistor configuration shown in figure 5 is used to measure the battery? tem - perature and scale it to operate from v ltf to v tco . resistors r t1 and r t2 are calculated to provide the required cutoff at v tco . see the design guide section for a detailed design example. maximum voltage termination the maximum voltage termination method is another safety feature designed to work if something is drastically wrong. under normal operation of the charger, this condi - tion should only be reached when the battery is removed. the maximum cell voltage expected is applied at the mcv pin using a resistor-divider network. if the cell volt - age measured at bat exceeds that at mcv, fast- charge is terminated. for most applications using both nicd and nimh batteries, this voltage (v mcv ) can be set to 1.9v. the max2003/max2003a do not terminate fast-charge if the maximum voltage is reached before the hold-off time has expired. if the cell voltage is greater than the mcv during the hold-off time, the device will continue fast-charge until the hold-off time has expired, and then it will terminate fast-charge. the hold-off time is deter - mined by the inputs tm1 and tm2, as shown in table 4. maximum timeout termination the final method is maximum timeout termination, which (like the maximum voltage and maximum tem - perature methods) is another backup safety feature. the timeout time depends on the charge rate selected and is set by the control signals tm1 and tm2. table 4 shows a list of different timeout periods available for dif - ferent control-signal inputs. if the timeout is reached before any other termination method is seen, fast- charge is terminated to protect the charger and battery. top-off charge top-off charge is used to provide the last bit of charge needed to reach full capacity after fast-charge is termi - nated. top-off charging puts slightly more energy into the battery than simple trickle charging, and can be used for both nicd and nimh batteries. select it by choosing the appropriate control signals on tm1 and tm2 (table 4). max2003/max2003a nicd/nimh batter y fast-char ge contr ollers ______________________________________________________________________________________ 11 *enable 100 23 4c v cc v cc disable 100 23 *enable 410 90 *enable 200 45 2c v cc open c v cc gnd *enable 820 180 c/2 open v cc 4c open open disable 410 90 disable 200 45 2c open gnd c gnd v cc disable 820 180 c/2 gnd open disable top-off charge 140 hold-off time ? v/mcv (sec) 360 fast- charge timeout (min) tm1 c/4 gnd gnd fast- charge rate tm2 table 4. programmable inputs for timeout/hold-off/fast-charge/top-off/ pulse trickle (v cc = 5v) 0.5 1 0.5 0.5 0.5 1 1 1 disable max2003a trickle charge (s) on/off * max2003 is on for 4sec and off for 30sec. max2003a is on for 0.5sec and off for 3.5sec. 16 32 64 128 16 32 64 128 544 max2003a sampling interval (sec) 544 136 68 68 544 136 68 68
max2003/max2003a the top-off charge is done at 1/8 the fast-charge rate. for the max2003, the mod pin is activated in every 34 second period to supply current to the battery for 4 seconds (mod oscillates for 4 seconds and stays low for 30 seconds) (figure 7). if external regulation is used (sns tied to ground), mod stays high for 4 seconds and low for 30 seconds (figure 8). this top-off process continues until the fast-charge timeout (table 4) is exceeded, or if a maximum temperature or maximum voltage condition is detected. the max2003a is slightly modified to turn the mod pin on for 0.5sec in every 4 second period. this shorter on-time reduces battery heat and increases charge acceptance. during the top- off charge, the chg pin will cycle low (led on) for 0.125sec and high (led off) for 0.125sec. trickle-charge a trickle-charge is applied to the battery after fast- charge and top-off charge have terminated to compen - sate for self discharge. there are two methods of trickle charge: constant and pulsed. pulsed trickle-charge (max2003a) the max2003a provides a pulsed trickle-charge to the battery by turning on the mod pin briefly during a fixed period of time. the duty cycle of the pulse is a function of the programmable inputs tm1 and tm2 (table 4 ). the max2003a does not use the trickle resistor to provide the trickle charge. however, the trickle resistor cannot be entirely omitted because it is also used for the battery- detect circuitry. constant trickle-charge (max2003) the max2003 provides a steady trickle-charge to the battery by connecting a resistor from the dc supply to the positive battery terminal. this resistor has a dual purpose, in that it provides a trickle-charge and pulls the bat pin above the mcv when the battery is absent. the trickle-charge rate depends on the type of battery used. for nicd batteries, a nominal trickle-charge rate would be c/16, and nimh batteries could use a rate of c/40. the resistor value used depends on the maxi - mum dc voltage and the typical battery voltage. for example, a six-cell 800mah nicd pack with a nominal voltage of 1.2v per cell would have a total voltage of 1.2v x 6v = 7.2v. if the dc supply voltage used is 14v, the voltage across the trickle resistor would be 14.0v - 7.2v = 6.8v. the trickle current needed would be c/16 = 800 / 16 = 50ma. the trickle resistor would therefore be r tr = 6.8v / 50ma 150 . similar calculations should be made for nimh batteries using c/40 as the trickle-charge rate. if a trickle-charge is not needed, a higher value of trick - le resistor (like 100k ) can be selected to sense the battery insertion. charge status the chg pin is connected to a led that indicates the operating mode. table 5 summarizes the different charge conditions. _______________________ design guide using the circuit of figure 1 as an example, the follow - ing nine steps show how to design a 1.7a switch-mode fast-charger that can charge a duracell dr17 (nimh six-cell battery pack with a 1700mah capacity). 1) select dc power supply . the first step is to select the dc power supply (such as a wall cube). the mini - mum supply voltage should have a supply equal to about 2v per cell, plus 1v headroom for external cir - cuitry ((2v/cell) + 1v). the minimum supply voltage must be greater than 6v. if, as in our example, there are six cells, a minimum supply of about 13v is needed ((6 cells x 2v) + 1v). 2) determine charge rate . the charge rate, or fast- charge current (i fast ), is determined by two factors: the capacity of the battery, and the time in which the user wants the battery to be charged. the battery man - ufacturer recommends a maximum fast-charge rate, which must not be exceeded. capacity of battery (mah) i fast (ma) = charge time (h) for example, if a 1700mah battery needs to be charged in two hours (c/2), a fast-charge current of at least 850ma is needed. a charge rate of c/2 will ideally charge a battery in two hours but, because of inefficiencies in a battery? chemical processes, the time could be 30% to 40% more. our example circuit (figure 1) charges the duracell battery pack at a c rate of 1.7a, which should fully charge a discharged battery in approximately 80 minutes. nicd/nimh batter y fast-char ge contr ollers 12 ______________________________________________________________________________________ table 5. charge status led on for 0.125sec, off for 0.125sec charge complete and top- off led on fast-charge led on for 1.375sec, off for 0.125sec discharge-before-charge led on for 0.125sec, off for 1.375sec charge pending charge state led off battery absent chg led status
3) select sense resistor . the sense resistor deter - mines the rate at which the battery is fast-charged. the sense pin, sns, has an average voltage of 235mv (see detailed description ) and, since the charge current (i fast ) is known from above, the resistor can be calcu - lated by: r sns = v sns / i fast = 0.235 / i fast in this example, a fast-charge current of 1.7a requires a sense resistor of about 0.14 (1 watt). 4) select tm1 and tm2 . once the charge rate is determined, table 4 can be used to select the tm1 and tm2 inputs. tm1 and tm2 set the safety timeout, hold- off time, and top-off enable (see fast-charge termination section in the detailed description ). in figure 1, a fast-charge rate of c with top-off would require tm1 to be gnd and tm2 to be v cc . 5) select r b1 and r b2 . the max2003a requires the user to select r b1 and r b2 to indicate the number of cells in the battery. the total resistance value (r b1 + r b2 ) should be between 100k and 500k to prevent any problems with noise. in figure 1 (with six cells) r b1 is selected to be 100k and, from the following equation: r b2 = r b1 / (number of cells - 1) = 100k / (6 - 1) r b2 can be calculated to be 20k . 6) select temperature-control components . most sealed rechargeable battery packs have a built-in ther - mistor to prevent air currents from corrupting the accurate temperature measurements. the thermistor size and tem - perature characteristics can be obtained from the bat - tery-pack manufacturer, to help in designing the rest of the circuit. three-terminal battery packs that incorporate a thermistor generally share a common connection for the thermistor and the battery negative terminal. large charg - ing currents may produce voltage drops across the com - mon negative connector, causing errors in thermistor readings. using separate contacts for the thermistor ground sense and the battery ground sense at the nega - tive battery terminal will reduce these errors. if an external thermistor is to be used, take care to ensure that it is placed in direct contact with the battery, and that the bat - tery/thermistor set-up is placed in a sealed container. neither nicd nor nimh batteries should be fast- charged outside the maximum and minimum tempera - ture limits. however, some applications also require termination using the ? t/ ? t criterion. the resistors r t1 and r t2 (figure 1) will determine the temperature cutoff (v tco ) and the rate-of-change of temperature ( ? t/ ? t). though nicd batteries do not always require termina - tion using the ? t/ ? t feature, it is not possible to isolate and disable this mode. it is therefore recommended that nicd and nimh batteries use the same ? t/ ? t termi - nation parameters. the duracell dr17 battery pack used in our example circuit recommended a low fault temperature (v ltf ) of +10 c and a maximum temperature cutoff (v tco ) of +50 c. these maximum temperature values will never be reached in most cases, but are used as a safety net to prevent battery damage. according to duracell, the 10k thermistor inside the pack varies from 17.96k at +10 c to 4.16k at +50 c. the circuit in figure 1 will be designed so that a battery temperature change of 1 c/min will result in fast-charge termination. at 1 c/min, the battery will take 40 minutes to change 40 c (10 c to 50 c). since a charge rate of c is used for this example, table 4 shows that the max2003a samples the ts pin every 68 seconds and compares it with a value taken 136 seconds earlier. the device will terminate fast-charge if the voltage at ts changes by more than 0.0032v cc (16mv for v cc = 5v). at a charge rate of 16mv every 136 seconds, the ts pin will charge 280mv in 40 minutes (40min x 60sec/min x 16mv/136sec). the low fault temperature (v ltf ) is set internally at 0.4v cc , which is 2.0v for a supply of 5v. the tempera - ture cutoff voltage (v tco ) will be 280mv below v ltf , or: v tco = (2.00v - 0.28v) = 1.72v figure 5 shows that, at any given temperature: v ts = v cc (r t2 || r ntc ) / [(r t2 || r ntc ) + r t1 ] when the battery temperature is +10 c, the voltage is: v ts10 = v cc (r t2 || r ntc10 ) / [(r t2 || r ntc10 ) + r t1 ] and at +50 c: v ts50 = v cc (r t2 || r ntc50 ) / [(r t2 || r ntc50 ) + r t1 ] max2003/max2003a nicd/nimh batter y fast-char ge contr ollers ______________________________________________________________________________________ 13 v cc r2 r3 r1 mcv tco figure 9. resistor configuration for mcv and tco
max2003/max2003a from solving these simultaneous equations: r t2 = [(x) (r ntc10 ) - (r ntc50 )] / (1 - x) r t1 = [(r t2 ) (r ntc10 ) (v cc - v ts10 )] / [v ts10 (r t2 + r ntc10 )]. [(r ntc50 )(v ts10 )(v cc - v ts50 )] where x = _____________________________ [(r ntc10 ) (v ts50 ) (v cc - v ts10 )] using r ntc50 = 4.16k , r ntc10 = 17.96k , v ts50 = 1.72v, and v ts10 = 2.00v, it can be calculated that r t1 = 1.599k and r t2 = 2.303k . select preferred resistor values for r t1 (2.21k ) and r t2 (1.62k ). the actual voltages on mcv and tco can be verified as follows: 7) select maximum cell voltage (mcv) and temperature cutoff (tco) . the mcv and tco can be selected with a resistor-divider combination (figure 9). in our example, tco has been set to +10 c, which cor - responds to a voltage of 1.72v at the ts pin. the mcv for most fast-charge batteries can be set to about 1.9v. to minimize the current load on v cc , choose r1 in the range of 20k to 200k . in this example, choose r1 = 60.4k , then calculate r3 and r2 as follows: r3 = (v tco x r1) / (v cc - v mcv ) = 33.5k (1%) and r2 = (v mcv x r1) / (v cc - v mcv ) - r3 = 3.51k (1%) select preferred resistor values for r2 (3.48k ) and r3 (33.2k ). the actual voltages on mcv and tco can be verified as follows : v tco = v cc (r3) / (r1 + r2 + r3) = 1.71v and v mcv = v cc (r2 + r3) / (r1 + r2 + r3) = 1.89v. 8) select trickle resistor (max2003 only). the trick - le resistor (r tr ) is selected to allow a trickle-charge rate of c/16 to c/40. the resistor value is given by: r tr = (v dc - v bat ) / i tr where i tr is the required trickle current, v dc is the dc supply voltage, and v bat is the number of cells times the cell voltage after fast-charge. in our example, the 1700mah nimh battery needs a trickle current of c/40; i.e., 42ma (1700mah/40h). therefore, the minimum voltage (from the formula above) is as follows: r tr = [13.0v - (6 x 1.2v)] / 42ma 150 the maximum power dissipated in the resistor can be calculated by: power = (v dc - v bat(min) ) 2 / r tr where v bat(min) is the minimum cell voltage, v dc is the dc supply voltage, and r tr is the trickle resistor value. since a shorted battery could have 0v, this must be the minimum cell voltage possible. therefore the power dissipated in the trickle resistor would be: power = (13 - 0) 2 / 150 = 1.2w a 2w, 150 resistor should be sufficient for the trickle- charge resistor. for the max2003a, refer to trickle- charge section. 9) select inductor . the inductor value can be calcu - lated using the formula: v l = l d i / d t where v l is the maximum voltage across the inductor, l is the minimum inductor value, d i is the change in induc - tor current, and t is the minimum on-time of the switch. v v r ii r r ii r r 5 1.62k ii 17.96k 1.62k ii 17.96k 2.21k 2.01v v v r ii r r ii r r 5 1.62k ii 4.16k 1.62k ii 4.16k 2.21k 1.72v ts10 cc t2 ntc10 t2 ntc10 t1 ts50 cc t2 ntc50 t2 ntc50 t1 = ( ) ( ) + [ ] = w w ( ) w w ( ) + w [ ] = = ( ) ( ) + [ ] = w w ( ) w w ( ) + w [ ] = nicd/nimh batter y fast-char ge contr ollers 14 ______________________________________________________________________________________ i load i max = 1.9a inductor current i min = 1.5a time d i = i max - i min t off t on figure 10. inductor-current waveform in continuous- conduction mode
in order to provide high currents with minimum ripple, the device must function in the continuous-conduction mode. figure 10 shows a current waveform of an inductor in the continuous-conduction mode (where the coil current never falls to zero). the average load current (i load ) through the inductor must be 1.7a, so a peak current (i max ) of 1.9a should give a fairly low ripple while keeping the inductor size minimal. this means that the total current change (figure 10) across the inductor is d i = 2 (1.9 - 1.7) = 0.4a. the maximum voltage across the inductor is present when the battery voltage is at its minimum. the mini - mum cell voltage at the start of fast-charge will be 1v per cell, giving a battery voltage of 6v for 6 cells. the maximum voltage (v l ) across the inductor is therefore: v l = (input voltage - minimum battery voltage) the input voltage for this application is 13v, so the maximum voltage is: v l = (13v - 6v) = 7v the minimum on-time d t of the switch is given by: d t = (v out / v in ) x period where v out is the minimum battery voltage, v in is the maximum input voltage, and period is the period of the switching signal. the maximum input voltage for this application will be 14v, and the maximum allowed switching frequency of 100khz gives a period of 10 s. the minimum on-time will therefore be: d t = (v out / v in ) x period = (6v / 13v) x 10 s = 4.62 s the inductor value can be calculated from: l = v d t / d i = (7v x 4.62 s) / 0.4a = 81 h. i f this inductor value is used, the actual switching fre - quency will be lower than the 100khz expected, due to comparator delays and variations in the duty cycle. the inductor value selected for our application will be 100 h? preferred value just above the calculated value. it is important to choose the saturation current rating of the inductor to be a little higher than the peak currents, to prevent the inductor from saturating during operation. the inductor must be selected to ensure that the switching frequency of the mod pin will not exceed the 100khz maximum. additional applications _________________________ infor mation the max2003/max2003a can use several other cir - cuits to charge batteries. figure 9 shows a circuit that uses a darlington transistor to regulate the current a six-cell nicd battery pack receives. figure 10 shows a gated current-limited supply being used to charge a duracell nimh battery pack. table 6 lists the external components used in these two application configura - tions. linear regulation of charge current the circuit in figure 11 uses an inexpensive transistor to provide the charge current. since the input for the max667 can tolerate up to 16v, this circuit can charge up to 7 cells. the max667 can be replaced with a dif - ferent regulator if more cells need to be charged. the dc source must supply a voltage equal to 2x the num - ber of cells, plus 2v overhead to accommodate the drop across external components. when fast-charge is initiated, the voltage at the sns pin is sampled and compared to the trip levels (220mv low and 250mv high). if the voltage at sns is below 220mv, the mod pin will switch high, and the 10k/1 f rc lowpass filter will pull high, turning on the npn tran - sistor. this will pull the base of the darlington tip115 low, turning it on and allowing current to flow into the battery. when the current through the battery and sns resistor are high enough, the voltage at sns will exceed 250mv and the mod pin will turn off. the amount of current the battery receives depends on the resistor between sns and v ss . in our example cir - cuit, the average current through the sns resistor will be: i sns(avg) = v sns(avg) / r sns = 0.235 / 0.28 = 0.84a the maximum current the resistor will receive is: i sns(max) = v sns(max) / r sns = 0.25 / 0.28 = 0.90a the darlington transistor must be biased to ensure that a minimum of 0.90a will be supplied. this minimum max2003/max2003a nicd/nimh batter y fast-char ge contr ollers ______________________________________________________________________________________ 15 table 6. external component sources (602) 994-6430 (602) 303-5454 motorola power mosfet & darlington transistor (904) 462-4726 (203) 791-3273 (904) 462-3911 energizer power systems (800) 431-2658 duracell battery (619) 549-4791 (510) 460-5498 fax number (800) 235-5445 alpha thermistor thermistor device (510) 734-3060 advanced power solutions power supply phone number manufacturer
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers 16 ______________________________________________________________________________________ max2003 max2003a max667 mod 3 r1 60.4k 1k 100k 1k r2 3.48k r3 33.2k 14 16 7 6 5 8 1 14v/2a dc source r tr 10k (*150 w (2w)) 2 5v out in 3 0.1 m f 47 m f 0.1 m f 47 m f *trickle-charge rate c/16 1n5822 0.1 m f 4 15 6 9 7 r b1 100k r b2 20k r sns 0.294 w 1% (1w) 800mah 6 nicd alpha curve a thermistor r dis 9 w (10w) ntc r t 100k r b 100k discharge rate 1c charge rate 1c c t 0.1 m f 1 m f c b 0.1 m f d g s to v cc r t1 2.21k 10k 10k tip115 heatsink 6.8k r t2 1.62k q2 n mmsf5no3hd q3 2n2222 5 4 2 1 12 13 11 10 dis ts sns bat v ss v cc v cc dven push to discharge tm2 tm1 dcmd temp chg mcv tc0 led led ccmd 8 q1 *component used for max2003. figure 11. linear mode to charge nicd batteries with - ? v termination
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers ______________________________________________________________________________________ 17 max2003 max2003a mod 5 r1 60.4k 1k 100k 1k r2 3.48k r3 33.2k 14 16 lm317 243 w r tr 10k *180 w (2w) q1 p mmdf3p03hd 22 m f 22 m f 22 m f 732 w adj 5v out in out 19v i limited v source 2.6a 0.1 m f 0.1 m f *trickle-charge rate c/40 1n5822 0.1 m f 15 6 9 7 r b1 80.6k r b2 10k 2600mah 9 nimh r dis 4 w (20w) ntc r t 100k r b 100k discharge rate 1c c t 0.1 m f c b 0.1 m f d g duracell dr35 s to v cc r t1 2.21k 12v zener 1k d s g 10k r t2 1.62k q2 n mmsf3n03hd q3 2n2222 2 4 1 3 12 13 11 10 dis ts sns bat v ss v cc v cc tm2 push to discharge tm1 dcmd temp chg mcv tc0 led led dven ccmd 1k charge rate 1c *component used for max2003. figure 12. current-limited mode for nimh batteries with ? t/ ? t termination
max2003/max2003a current value must be sufficiently guardbanded to ensure the limiting factor is the sns resistor, and not the transistor. in our example, the maximum current supplied by the darlington will be guardbanded to 1.8a. since the beta of the darlington is typically 1000, the base current needed will be: i b = i c / beta = 1.8a / 1000 = 1.8ma the emitter of the tip115 will see 14v, so the base will see about 12.6v. when the mod pin is high, the 2n2222 transistor is on and the base resistor will be: r b = v b / i b = 12.6v / 1.8ma 6.8k this 1.8a current will never be reached because mod will be off when the sns voltage reaches 0.25v (0.9a). current-limited supply the circuit in figure 12 is set up to charge a duracell dr35 battery pack (nine cells, 2.6ah) using a 19v, 2.6a current-limited power supply provided by advanced power solutions. since many power supplies have built-in current limiting, very few external components are required for this charging method. the sns pin in this circuit is tied directly to v ss . this signals the mod pin to stay high until a termination condition is met. when mod is high, the npn transistor is turned on, hence pulling the gate of the mosfet low. this turns the mosfet on and supplies current to the battery at the current limit of the source (2.6a). the 12v zener diode is placed between the source and gate of the fet to ensure the fet? maximum source-drain voltage is not exceeded. when a termination condition is reached, the mod pin goes low to turn off the fet and terminate the fast- charge current. nicd/nimh batter y fast-char ge contr ollers 18 ______________________________________________________________________________________ table 7. operation summary discharge initiated with temperature and voltage within set limits. discharge fast-charge initiated and tempera - ture or voltage outside the set limits. charge pending a) power applied and voltage at ccmd = dcmd b ) dcmd = low, ccmd = rising edge (power already present) c ) dcmd = high, ccmd = falling edge (power already present) initiate fast-charge rising edge on dcmd initiate discharge charge status (v bat - v sns ) 3 v mcv battery absent conditions low low low low low mod status high low low low low dis status 1.375 0.125 chg led status 0.125 1.375 continuous continuous continuous pulse current provided by pulsing mod pin after fast-charge/top-off. pulsed trickle- charge (max2003a) trickle current provided by external resistor after fast-charge/top-off. constant trickle- charge (max2003) charge complete and top-off enabled without exceeding temper - ature and voltage limits. top-off charge exceed one of the five termination conditions. charge complete fast-charge initiated with tempera - ture and voltage within set limits. fast-charge pulsed according to charge rate (table 4). low max2003a: activate for 0.5sec in every 4sec period. max2003: active for 4sec in every 34sec period. low if v sns > 0.050v cc , mod = low if v sns > 0.044v cc , mod = high low low low low low 0.125 0.125 0.125 0.125 continuous 0.125 0.125 0.125 0.125 led on (low) (sec) led off (high) (sec)
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers ______________________________________________________________________________________ 19 chip t opography mod dcmd ccmd 0.089" (2.261mm) 0.086" (2.184mm) bat dven dis v cc chg temp mcv tm1 tm2 ts v ss sns tco transistor count: 5514 substrate connected to v ss ________________________________________________________ package infor mation soicn.eps
max2003/max2003a nicd/nimh batter y fast-char ge contr ollers 20 ______________________________________________________________________________________ ___________________________________________ package infor mation (continued) soicw.eps pdipn.eps

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