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for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. general description the max712/MAX713 fast charge nickel metal hydride (nimh) and nickel cadmium (nicd) batteries from a dc source at least 1.5v higher than the maximum battery voltage. 1 to 16 series cells can be charged at rates up to 4c. a voltage-slope detecting analog-to-digital convert- er, timer, and temperature window comparator determine charge completion. the max712/MAX713 are powered by the dc source via an on-board +5v shunt regulator. they draw a maximum of 5? from the battery when not charging. a low-side current-sense resistor allows the battery charge current to be regulated while still supplying power to the battery? load. the max712 terminates fast charge by detecting zero voltage slope, while the MAX713 uses a negative voltage-slope detection scheme. both parts come in 16- pin dip and so packages. an external power pnp tran- sistor, blocking diode, three resistors, and three capacitors are the only required external components. for high-power charging requirements, the max712/ MAX713 can be configured as a switch-mode battery charger that minimizes power dissipation. two evaluation kits are available: order the max712evkit-dip for quick evaluation of the linear charger, and the MAX713evkit- so to evaluate the switch-mode charger. ________________________applications battery-powered equipment laptop, notebook, and palmtop computers handy-terminals cellular phones portable consumer products portable stereos cordless phones features fast charge nimh or nicd batteries voltage slope, temperature, and timer fast-charge cutoff charge 1 to 16 series cells supply battery? load while charging (linear mode) fast charge from c/4 to 4c rate c/16 trickle-charge rate automatically switch from fast to trickle charge linear or switch-mode power control 5a max drain on battery when not charging 5v shunt regulator powers external logic max712/MAX713 nicd/nimh battery fast-charge controllers ________________________________________________________________ maxim integrated products 1 max712 MAX713 thi r2 150 ? r3 68k ? r4 22k ? r1 10 f c4 0.01 f c1 1 f c3 10 f c2 0.01 f drv q1 2n6109 dc in wall cube see figure 19 for switch-mode charger circuit. d1 1n4001 battery r sense v+ vlimit batt+ ref temp batt- tlo gnd cc load typical operating circuit 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 ref v+ drv gnd batt- cc pgm3 pgm2 vlimit batt+ pgm0 pgm1 thi tlo temp fastchg top view max712 MAX713 dip/so pin configuration 19-0100; rev 4; 1/01 part max712 cpe max712cse max712c/d 0? to +70? 0? to +70? 0? to +70? temp. range pin-package 16 plastic dip 16 narrow so dice* ordering information ordering information continued at end of data sheet. * contact factory for dice specifications. ** contact factory for availability and processing to mil-std-883. max712epe max712ese max712mje -55? to +125? -40? to +85? -40? to +85? 16 plastic dip 16 narrow so 16 cerdip** evaluation kit available
max712/MAX713 nicd/nimh battery fast-charge controllers 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (i v+ = 10ma, t a = t min to t max , unless otherwise noted. refer to typical operating circuit . all measurements are with respect to batt-, not gnd.) 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. v+ to batt- .................................................................-0.3v, +7v batt- to gnd ........................................................................?v batt+ to batt- power not applied............................................................?0v with power applied ................................the higher of ?0v or ?v x (programmed cells) drv to gnd ..............................................................-0.3v, +20v fastchg to batt- ...................................................-0.3v, +12v all other pins to gnd......................................-0.3v, (v+ + 0.3v) v+ current.........................................................................100ma drv current. .....................................................................100ma ref current.........................................................................10ma continuous power dissipation (t a = +70?) plastic dip (derate 10.53mw/? above +70?............842mw narrow so (derate 8.70mw/? above +70? .............696mw cerdip (derate 10.00mw/? above +70? ................800mw operating temperature ranges max71_c_e .......................................................0? to +70? max71_e_e .................................................... -40? to +85? max71_mje ................................................. -55? to +125? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? v drv = 10v v+ = 0v, batt+ = 17v pgm3 = batt- 5ma < i v+ < 20ma pgm3 = ref pgm3 = open pgm3 = v+ 0v < temp < 2v, temp voltage rising v limit = v+ per cell pgm0 = pgm1 = batt-, batt+ = 30v 1.2v < v limit < 2.5v, 5ma < i drv < 20ma, pgm0 = pgm1 = v+ 0ma < i ref < 1ma conditions ma 30 drv sink current % -1.5 1.5 battery-voltage to cell-voltage divider accuracy % -15 15 timer accuracy mv 26.0 31.3 38.0 trickle-charge vsense 12.0 15.6 20.0 4.5 7.8 12.0 1.5 3.9 7.0 mv 225 250 275 fast-charge vsense v 1.6 1.65 1.7 internal cell voltage limit mv -30 30 vlimit accuracy ? -1 1 thi, tlo, temp, vlimit input bias current ? 5 batt+ leakage ma 5 i v+ (note 1) v 4.5 5.5 v+ voltage mv -10 10 thi, tlo offset voltage (note 2) v 02 thi, tlo, temp input range v 1.25 2.50 external vlimit input range v 0.35 0.50 undervoltage lockout k ? 30 batt+ resistance with power on ? 0.5 c1 capacitance nf 5 c2 capacitance v 1.96 2.04 ref voltage units min typ max parameter max712 MAX713 mv/t a per cell 0 voltage-slope sensitivity (note 3) -2.5
electrical characteristics (continued) (i v + = 10ma, t a = t min to t max , unless otherwise noted. refer to typical operating circuit . all measurements are with respect to batt-, not gnd.) note 1: the max712/MAX713 are powered from the v+ pin. since v+ shunt regulates to +5v, r1 must be small enough to allow at least 5ma of current into the v+ pin. note 2: offset voltage of thi and tlo comparators referred to temp. note 3: t a is the a/d sampling interval (table 3). note 4: this specification can be violated when attempting to charge more or fewer cells than the number programmed. to ensure proper voltage-slope fast-charge termination, the (maximum battery voltage) (number of cells programmed) must fall within the a/d input range. max712/MAX713 nicd/nimh battery fast-charge controllers _______________________________________________________________________________________ 3 battery voltage number of cells programmed v fastchg = 10v v fastchg = 0.4v conditions v 1.4 1.9 a/d input range (note 4) ? 10 fastchg high current ma 2 fastchg low current units min typ max parameter typical operating characteristics (t a = +25?, unless otherwise noted.) 20 1k 100k 1m 10k 10m current-sense amplifier frequency response (with 15pf) -20 frequency (hz) gain (db) phase (degrees) -10 0 10 40 -120 -80 -40 0 c2 = 15pf fastchg = 0v v out v in current- sense amp batt- batt- cc gnd - - + + a v max712/13 toc01 20 -10 -20 10 1k current-sense amplifier frequency response (with 10nf) 0 10 40 -80 -120 -40 0 frequency (hz) gain (db) phase (degrees) 100 10k c2 = 10nf fastchg = 0v a v max712/13 toc02 100 0.1 1.95 1.97 2.01 2.05 current error-amplifier transconductance 1 10 voltage on cc pin (v) drv pin sink current(ma) 1.99 2.03 fastchg = 0v, v+ = 5v max712/13 toc03 5.8 4.8 060 shunt-regulator voltage vs. current 5.6 current into v+ pin (ma) v+ voltage (v) 30 5.2 5.0 10 20 50 5.4 4.0 4.4 4.2 4.6 40 drv not sinking current drv sinking current max712/13 toc04 1.0 060 alpha thermistor part no. 13a1002 steinhart-hart interpolation 1.6 battery temperature( c) temp pin voltage (v) battery thermistor resistance (k ? ) 30 1.4 1.2 10 20 50 0.2 0.6 0.4 0.8 20 35 30 25 0 10 5 15 40 max712/13 toc05
max712/MAX713 nicd/nimh battery fast-charge controllers 4 _______________________________________________________________________________________ typical operating characteristics (continued) (t a = +25?, unless otherwise noted.) 90 MAX713 nimh battery charging characteristics at c rate charge time (minutes) 030 60 v t max712/13 toc07 ? v ? t cutoff 1.60 cell voltage (v) cell temperature ( c) 1.45 1.55 1.50 40 25 35 30 1.40 0 MAX713 nicd battery-charging characteristics at c/2 rate 1.45 charge time (minutes) cell voltage (v) cell temperature ( c) 1.50 25 30 35 50 150 100 ? v ? t cutoff v t max712/13 toc08 MAX713 nimh battery charging characteristics at c rate 150 MAX713 nimh battery charging characteristics at c/2 rate 1.55 1.40 050 1.50 1.45 40 25 35 30 v t ? v ? t cutoff charge time (minutes) cell voltage (v) cell temperature ( c) 100 max712/13 toc09 15 20 MAX713 charging characteristics of a fully-charged nimh battery 1.60 charge time (minutes) cell voltage (v) cell temperature ( c) 1.45 1.65 05 1.55 1.50 40 25 35 30 10 v t ? v ? t cutoff 5 minute rest between charges max712/13 toc10 1.45 0 MAX713 charging characteristics of a fully charged nimh battery 1.50 charge time (minutes) cell voltage (v) cell temperature ( c) 1.60 1.65 1.55 25 30 40 35 515 10 5-hour rest between charges ? v ? t cutoff v t 20 max712/13 toc11 90 MAX713 nicd battery charging characteristics at c rate 1.55 charge time (minutes) cell voltage (v) cell temperature ( c) 1.40 030 1.50 1.45 40 25 35 30 60 v t ? v ? t cutoff max712/13 toc06
max712/MAX713 nicd/nimh battery fast-charge controllers _______________________________________________________________________________________ 5 pin description compensation input for constant current regulation loop cc 11 negative terminal of battery batt- 12 system ground. the resistor placed between batt- and gnd monitors the current into the battery. gnd 13 current sink for driving the external pnp current source drv 14 shunt regulator. the voltage on v+ is regulated to +5v with respect to batt-, and the shunt current powers the max712/MAX713. v+ 15 trip point for the under-temperature comparator. if the max712/MAX713 power on with the voltage-on temp less than tlo, fast charge is inhibited and will not start until temp rises above tlo. tlo 6 sense input for temperature-dependent voltage from thermistors. temp 7 open-drain, fast-charge status output. while the max712/MAX713 fast charge the battery, fastchg sinks current. when charge ends and trickle charge begins, fastchg stops sinking current. fastchg 8 pgm2 and pgm3 set the maximum time allowed for fast charging. timeouts from 33 minutes to 264 minutes can be set by connecting to any of v+, ref, or batt-, or by leaving the pin open (table 3). pgm3 also sets the fast-charge to trickle-charge current ratio (table 5). pgm2, pgm3 9, 10 trip point for the over-temperature comparator. if the voltage-on temp rises above thi, fast charge ends. thi 5 pgm0 and pgm1 set the number of series cells to be charged. the number of cells can be set from 1 to 16 by connecting pgm0 and pgm1 to any of v+, ref, or batt-, or by leaving the pin open (table 2). for cell counts greater than 11, see the linear-mode, high series cell count section. charging more or fewer cells than the number programmed may inhibit ? v fast-charge termination. pgm0, pgm1 3, 4 pin positive terminal of battery batt+ 2 sets the maximum cell voltage. the battery terminal voltage (batt+ - batt-) will not exceed vlimit x (number of cells). do not allow vlimit to exceed 2.5v. tie vlimit to vref for normal operation. vlimit 1 function name 2v reference output ref 16
max712/MAX713 nicd/nimh battery fast-charge controllers 6 _______________________________________________________________________________________ getting started the max712/MAX713 are simple to use. a complete linear-mode or switch-mode fast-charge circuit can be designed in a few easy steps. a linear-mode design uses the fewest components and supplies a load while charging, while a switch-mode design may be neces- sary if lower heat dissipation is desired. 1) follow the battery manufacturer? recommendations on maximum charge currents and charge-termination methods for the specific batteries in your application. table 1 provides general guidelines. 2) decide on a charge rate (tables 3 and 5). the slow- est fast-charge rate for the max712/MAX713 is c/4, because the maximum fast-charge timeout period is 264 minutes. a c/3 rate charges the battery in about three hours. the current in ma required to charge at this rate is calculated as follows: i fast = (capacity of battery in mah) (charge time in hours) depending on the battery, charging efficiency can be as low as 80%, so a c/3 fast charge could take 3 hours and 45 minutes. this reflects the efficiency with which electrical energy is converted to chemical energy within the battery, and is not the same as the power- conversion efficiency of the max712/MAX713. 3) decide on the number of cells to be charged (table 2). if your battery stack exceeds 11 cells, see the linear- mode high series cell count section. whenever changing the number of cells to be charged, pgm0 and pgm1 must be adjusted accordingly. attempting to charge more or fewer cells than the number pro- grammed can disable the voltage-slope fast-charge termination circuitry. the internal adc? input volt- age range is limited to between 1.4v and 1.9v (see the electrical characteristics ), and is equal to the voltage across the battery divided by the number of cells programmed (using pgm0 and pgm1, as in table 2). when the adc? input voltage falls out of its specified range, the voltage-slope termination cir- cuitry can be disabled. 4) choose an external dc power source (e.g., wall cube). its minimum output voltage (including ripple) must be greater than 6v and at least 1.5v higher (2v for switch mode) than the maximum battery voltage while charging. this specification is critical because normal fast-charge termination is ensured only if this requirement is maintained (see powering the max712/MAX713 section for more details). 5) for linear-mode designs, calculate the worst-case power dissipation of the power pnp and diode (q1 and d1 in the typical operating circuit ) in watts, using the following formula: pd pnp = (maximum wall-cube voltage under load - minimum battery voltage) x (charge current in amps) if the maximum power dissipation is not tolerable for your application, refer to the detailed description or use a switch-mode design (see switch-mode operation in the applications information section, and see the MAX713 ev kit manual). 6) for both linear and switch-mode designs, limit cur- rent into v+ to between 5ma and 20ma. for a fixed or narrow-range input voltage, choose r1 in the typical operation circuit using the following formula: r1 = (minimum wall-cube voltage - 5v) / 5ma for designs requiring a large input voltage variation, choose the current-limiting diode d4 in figure 19. 7) choose r sense using the following formula: rsense = 0.25v / (i fast ) 8) consult tables 2 and 3 to set pin-straps before applying power. for example, to fast charge at a rate of c/2, set the timeout to between 1.5x or 2x the charge period, three or four hours, respectively. < c/2 ? v/ ? t and/or temperature, max712 ? v/ ? t and/or temperature, MAX713 nimh batteries nicd batteries > 2c ? v/ ? t and temperature, max712 or MAX713 ? v/ ? t and/or temperature, MAX713 2c to c/2 ? v/ ? t and/or temperature, max712 or MAX713 ? v/ ? t and/or temperature, MAX713 charge rate table 1. fast-charge termination methods
max712/MAX713 nicd/nimh battery fast-charge controllers _______________________________________________________________________________________ 7 table 2. programming the number of cells table 3. programming the maximum charge time control logic +5v shunt regulator timer pgm2 pgm3 v+ batt- batt- under_voltage batt- drv v+ ref 100k ? 100k ? n hot ? v_detect timed_out batt- fastchg gnd cc batt- gnd cell_voltage internal impedance of pgm0?gm3 pins fast_charge power_on_reset in_regulation vlimit batt+ pgm0 pgm1 pgm2 pgm3 pgmx thi temp tlo ? v detection temperature comparators current and voltage regulator cold 0.4v max712 MAX713 figure 1. block diagram pgm1 connection pgm0 connection 1 v+ v+ number of cells 2 open v+ 4 batt- v+ 3 ref v+ 6 open open 5 v+ open 8 batt- open 7 ref open 10 open ref 9 v+ ref 12 batt- ref 11 ref ref 14 open batt- 13 v+ batt- 16 batt- batt- 15 ref batt- 22 v+ ref pgm3 conn pgm2 conn 22 v+ open 33 v+ batt- timeout (min) 33 v+ v+ 45 open ref 45 open open 66 open batt- 66 open v+ 90 ref ref 90 ref open 132 ref batt- 132 ref v+ 180 batt- ref 180 batt- open 264 batt- batt- 264 batt- v+ 21 21 21 a/d sampling interval (s) (t a ) 21 42 42 42 42 84 84 84 84 168 168 168 168 enabled disabled enabled voltage- slope termination disabled enabled disabled enabled disabled enabled disabled enabled disabled enabled disabled enabled disabled
max712/MAX713 nicd/nimh battery fast-charge controllers 8 _______________________________________________________________________________________ _______________detailed description the max712/MAX713 fast charge nimh or nicd batter- ies by forcing a constant current into the battery. the max712/MAX713 are always in one of two states: fast charge or trickle charge. during fast charge, the current level is high; once full charge is detected, the current reduces to trickle charge. the device monitors three variables to determine when the battery reaches full charge: voltage slope, battery temperature, and charge time. figure 1 shows the block diagram for the max712/ MAX713. the timer, voltage-slope detection, and temper- ature comparators are used to determine full charge state. the voltage and current regulator controls output voltage and current, and senses battery presence. figure 2 shows a typical charging scenario with batteries already inserted before power is applied. at time 1, the max712/MAX713 draw negligible power from the bat- tery. when power is applied to dc in (time 2), the power-on reset circuit (see the power - _on - _reset sig- nal in figure 1) holds the max712/MAX713 in trickle charge. once power - _on - _reset goes high, the device enters the fast-charge state (time 3) as long as the cell voltage is above the undervoltage lockout (uvlo) volt- age (0.4v per cell). fast charging cannot start until (bat- tery voltage) / (number of cells) exceeds 0.4v. when the cell voltage slope becomes negative, fast charge is terminated and the max712/MAX713 revert to trickle-charge state (time 4). when power is removed (time 5), the device draws negligible current from the battery. figure 3 shows a typical charging event using tempera- ture full-charge detection. in the case shown, the bat- tery pack is too cold for fast charging (for instance, brought in from a cold outside environment). during time 2, the max712/MAX713 remain in trickle-charge state. once a safe temperature is reached (time 3), fast charge starts. when the battery temperature exceeds the limit set by thi, the max712/MAX713 revert to trick- le charge (time 4). 0 a ma a 1 0.4 time voltage cell voltage (v) current into cell cell temperature 1.4 1.5 1.3 2 4 5 3 1. no power to charger 2. cell voltage less than 0.4v 3. fast charge 4. trickle charge 5. charger power removed temperature figure 2. typical charging using voltage slope a ma a 1 time cell temperature current into cell tlo thi 24 3 1. no power to charger 2. cell temperature too low 3. fast charge 4. trickle charge figure 3. typical charging using temperature a 1.5 1.4 1.3 ma a 1 time vref = vlimit cell voltage (v) current into cell 24 3 1. battery not inserted 2. fast charge 3. trickle charge 4. battery removed figure 4. typical charging with battery insertion
max712/MAX713 nicd/nimh battery fast-charge controllers _______________________________________________________________________________________ 9 the max712/MAX713 can be configured so that voltage slope and/or battery temperature detects full charge. figure 4 shows a charging event in which a battery is inserted into an already powered-up max712/MAX713. during time 1, the charger? output voltage is regulated at the number of cells times vlimit. upon insertion of the battery (time 2), the max712/MAX713 detect cur- rent flow into the battery and switch to fast-charge state. once full charge is detected, the device reverts to trickle charge (time 3). if the battery is removed (time 4), the max712/MAX713 remain in trickle charge and the output voltage is once again regulated as in time 1. powering the max712/MAX713 ac-to-dc wall-cube adapters typically consist of a trans- former, a full-wave bridge rectifier, and a capacitor. figures 10?2 show the characteristics of three con- sumer product wall cubes. all three exhibit substantial 120hz output voltage ripple. when choosing an adapter for use with the max712/MAX713, make sure the lowest wall-cube voltage level during fast charge and full load is at least 1.5v higher (2v for switch mode) than the maxi- mum battery voltage while being fast charged. typically, the voltage on the battery pack is higher during a fast- charge cycle than while in trickle charge or while supply- ing a load. the voltage across some battery packs may approach 1.9v/cell. 2n3904 d1 q1 v+ drv dc in r1 r2 max712 MAX713 figure 5. drv pin cascode connection (for high dc in voltage or to reduce max712/MAX713 power dissipation in linear mode) 1 x under_voltage i i n n _ _ r r e e g g u u l l a a t t i i o o n n 0 x x x x p p o o w w e e r r _ _ o o n n _ _ r r e e s s e e t t x 1 0 0 x x 1 0 0 1 0 0 1 0 1 0 1 0 0 1 0 0 1 x x 1 x x 1 0 1 0 table 4. max712/MAX713 charge-state transition table ? x c c o o l l d d x 0 x 1 x 1 1 1 1 x 0 x x x h h o o t t x x x 1 0 1 1 1 1 1 0 x x x no change result* set trickle no change no change set fast no change*** no change no change set fast set fast set fast** no change*** trickle to fast transition inhibited trickle to fast transition inhibited set trickle set trickle 1 x x x set trickle ? only two states exist: fast charge and trickle charge. * regardless of the status of the other logic lines, a timeout or a voltage-slope detection will set trickle charge. ** if the battery is cold at power-up, the first rising edge on cold will trigger fast charge; however, a second rising edge will have no effect. *** batteries that are too hot when inserted (or when circuit is powered up) will not enter fast charge until they cool and power i s recycled.
max712/MAX713 nicd/nimh battery fast-charge controllers 10 ______________________________________________________________________________________ the 1.5v of overhead is needed to allow for worst-case voltage drops across the pass transistor (q1 of typical operating circuit ), the diode (d1), and the sense resistor (r sense ). this minimum input voltage require- ment is critical, because violating it can inhibit proper termination of the fast-charge cycle. a safe rule of thumb is to choose a source that has a minimum input voltage = 1.5v + (1.9v x the maximum number of cells to be charged). when the input voltage at dc in drops below the 1.5v + (1.9v x number of cells), the part oscillates between fast charge and trickle charge and might never completely terminate fast-charge. the max712/MAX713 are inactive without the wall cube attached, drawing 5? (max) from the battery. diode d1 prevents current conduction into the drv pin. when the wall cube is connected, it charges c1 through r1 (see typical operating circuit ) or the current-limiting diode (figure 19). once c1 charges to 5v, the internal shunt regulator sinks current to regulate v+ to 5v, and fast charge commences. the max712/MAX713 fast charge until one of the three fast-charge terminating conditions is triggered. if dc in exceeds 20v, add a cascode connection in series with the drv pin as shown in figure 5 to prevent exceeding drv? absolute maximum ratings. furthermore, if figure 19? dc in exceeds 15v, a tran- sistor level-shifter is needed to provide the proper volt- age swing to the mosfet gate. see the MAX713 ev kit manual for details. select the current-limiting component (r1 or d4) to pass at least 5ma at the minimum dc in voltage (see step 6 in the getting started section). the maximum current into v+ determines power dissipation in the max712/MAX713. maximum current into v+ = (maximum dc in voltage - 5v) / r1 power dissipation due to shunt regulator = 5v x (maximum current into v+) sink current into the drv pin also causes power dissipa- tion. do not allow the total power dissipation to exceed the specifications shown in the absolute maximum ratings . fast charge the max712/MAX713 enter the fast-charge state under one of the following conditions: 1) upon application of power (batteries already installed), with battery current detection (i.e., gnd voltage is less than batt- voltage), and temp higher than tlo and less than thi and cell voltage higher than the uvlo voltage. 2) upon insertion of a battery, with temp higher than tlo and lower than thi and cell voltage higher than the uvlo voltage. r sense sets the fast-charge current into the battery. in fast charge, the voltage difference between the batt- and gnd pins is regulated to 250mv. drv current increases its sink current if this voltage difference falls below 250mv, and decreases its sink current if the volt- age difference exceeds 250mv. fast-charge current (i fast ) = 0.25v / r sense trickle charge selecting a fast-charge current (i fast ) of c/2, c, 2c, or 4c ensures a c/16 trickle-charge current. other fast- charge rates can be used, but the trickle-charge current will not be exactly c/16. batt- x v+ open ref batt- 1 0 0 0 0 8 512 256 128 64 current-sense amplifier pgm3 fast_charge av 1.25v v+ dc in gnd drv gnd cc batt- r sense d1 ref vlimit cell_voltage batt- batt- in_regulation c2 figure 6. current and voltage regulator (linear mode)
max712/MAX713 nicd/nimh battery fast-charge controllers ______________________________________________________________________________________ 11 the max712/MAX713 internally set the trickle-charge current by increasing the current amplifier gain (figure 6), which adjusts the voltage across r sense (see trickle-charge v sense in the electrical characteristics table ) . nonstandard trickle-charge current example configuration: typical operating circuit 2 x panasonic p-50aa 500mah aa nicd batteries c/3 fast-charge rate 264-minute timeout negative voltage-slope cutoff enabled minimum dc in voltage of 6v settings: use MAX713 pgm0 = v+, pgm1 = open, pgm2 = batt-, pgm3 = batt-, r sense = 1.5 ? (fast-charge current, i fast = 167ma), r1 = (6v - 5v) / 5ma = 200 ? since pgm3 = batt-, the voltage on r sense is regulat- ed to 31.3mv during trickle charge, and the current is 20.7ma. thus the trickle current is actually c/25, not c/16. further reduction of trickle-charge current for nimh batteries the trickle-charge current can be reduced to less than c/16 using the circuit in figure 7. in trickle charge, some of the current will be shunted around the battery, since q2 is turned on. select the value of r7 as follows: r7 = (v batt + 0.4v) / (l trlckle - i batt ) where v batt = battery voltage when charged i trlckle = max712/MAX713 trickle-charge current setting i batt = desired battery trickle-charge current regulation loop the regulation loop controls the output voltage between the batt+ and batt- terminals and the current through the battery via the voltage between batt- and gnd. the sink current from drv is reduced when the output voltage exceeds the number of cells times v limit , or when the battery current exceeds the pro- grammed charging current. for a linear-mode circuit, this loop provides the following functions: 1) when the charger is powered, the battery can be removed without interrupting power to the load. 2) if the load is connected as shown in the typical operating circuit , the battery current is regulated regardless of the load current (provided the input power source can supply both). voltage loop the voltage loop sets the maximum output voltage between batt+ and batt-. if v limit is set to less than 2.5v, then: maximum batt+ voltage (referred to batt-) = v limit x (number of cells as determined by pgm0, pgm1) vlimit should be set between 1.9v and 2.5v. if vlimit is set below the maximum cell voltage, proper termination of the fast-charge cycle might not occur. cell voltage can approach 1.9v/cell, under fast charge, in some battery packs. tie v limit to v ref for normal operation . with the battery removed, the max712/MAX713 do not provide constant current; they regulate batt+ to the maximum voltage as determined above. open 2c i fast /32 fast-charge rate trickle-charge current (i trickle ) v+ 4c i fast /64 batt- c/2 i fast /8 pgm3 ref c i fast /16 table 5. trickle-charge current determination from pgm3 fastchg r sense battery r7 q2 10k v+ 10k drv d1 q1 dc in gnd max712 MAX713 figure 7. reduction of trickle current for nimh batteries (linear mode)
max712/MAX713 nicd/nimh battery fast-charge controllers 12 ______________________________________________________________________________________ the voltage loop is stabilized by the output filter capacitor. a large filter capacitor is required only if the load is going to be supplied by the max712/MAX713 in the absence of a battery. in this case, set c out as: c out (in farads) = (50 x i load ) / (v out x bw vrl ) where bw vrl = loop bandwidth in hz (10,000 recommended) c out > 10? i load = external load current in amps v out = programmed output voltage (v limit x number of cells) current loop figure 6 shows the current-regulation loop for a linear- mode circuit. to ensure loop stability, make sure that the bandwidth of the current regulation loop (bw crl ) is lower than the pole frequency of transistor q1 (f b ). set bw crl by selecting c2. bw crl in hz = gm / c2, c2 in farads, gm = 0.0018 siemens the pole frequency of the pnp pass transistor, q1, can be determined by assuming a single-pole current gain response. both f t and b o should be specified on the data sheet for the particular transistor used for q1. f b in hz = f t / b o , f t in hz, b o = dc current gain condition for stability of current-regulation loop: bw crl < f b the max712/MAX713 dissipate power due to the cur- rent-voltage product at drv. do not allow the power dissipation to exceed the specifications shown in the absolute maximum ratings . drv power dissipation can be reduced by using the cascode connection shown in figure 5 or by using a switch-mode circuit. power dissipation due to drv sink current = (current into drv) x (voltage on drv) voltage-slope cutoff the max712/MAX713? internal analog-to-digital con- verter has 2.5mv of resolution. it determines if the bat- tery voltage is rising, falling, or unchanging by comparing the battery? voltage at two different times. after power-up, a time interval of t a ranging from 21sec to 168sec passes (see table 3 and figure 8), then a battery voltage measurement is taken. it takes 5ms to perform a measurement. after the first measurement is complete, another t a interval passes, and then a second measurement is taken. the two measurements are compared, and a decision whether to terminate charge is made. if charge is not terminated, another full two-measurement cycle is repeated until charge is terminated. note that each cycle has two t a intervals and two voltage measurements. the max712 terminates fast charge when a compari- son shows that the battery voltage is unchanging. the MAX713 terminates when a conversion shows the bat- tery voltage has fallen by at least 2.5mv per cell. this is the only difference between the max712 and MAX713. temperature charge cutoff figure 9a shows how the max712/MAX713 detect over- and under-temperature battery conditions using negative temperature coefficient thermistors. use the same model thermistor for t1 and t2 so that both have the same nominal resistance. the voltage at temp is 1v (referred to batt-) when the battery is at ambient temperature. the threshold chosen for thi sets the point at which fast charging terminates. as soon as the voltage-on temp rises above thi, fast charge ends, and does not restart after temp falls below thi. the threshold chosen for tlo determines the tem- perature below which fast charging will be inhibited. if tlo > temp when the max712/MAX713 start up, fast charge will not start until tlo goes below temp. the cold temperature charge inhibition can be disabled by removing r5, t3, and the 0.022 f capacitor; and by tying tlo to batt-. to disable the entire temperature comparator charge- cutoff mechanism, remove t1, t2, t3, r3, r4, and r5, and their associated capacitors, and connect thi to v+ and tlo to batt-. also, place a 68kq resistor from ref to temp, and a 22k ? resistor from batt- to temp. some battery packs come with a temperature-detecting thermistor connected to the battery pack? negative 5 ms 5 ms 5 ms 5 ms 5 ms 5 ms t a t a t a t a t a t a interval note: slope proportional to vbatt interval interval interval interval interval negative residual positive residual zero residual voltage rises 0t zero voltage slope cutoff for max712 negative voltage slope cutoff for max712 or MAX713 counts figure 8. voltage slope detection
max712/MAX713 nicd/nimh battery fast-charge controllers ______________________________________________________________________________________ 13 terminal. in this case, use the configuration shown in figure 9b. thermistors t2 and t3 can be replaced by standard resistors if absolute temperature charge cut- off is acceptable. all resistance values in figures 9a and 9b should be chosen in the 10k ? to 500k ? range. __________applications information switch-mode operation for applications where the power dissipation in the pass transistor cannot be tolerated (ie., where heat sinking is not feasible or is too costly), a switch-mode charger is recommended. switch-mode operation can be implemented simply by using the circuit of figure 19. the circuit of figure 19 uses the error amplifier at the cc pin as a comparator with the 33pf capacitor adding hysteresis. figure 19 is shown configured to charge two cells at 1a. lower charge currents and a different number of cells can be accommodated simply by changing r sense and pgm0?gm3 connections (tables 2 and 3). the input power-supply voltage range is 8v to 15v and must be at least 2v greater than the peak battery voltage, under fast charge. as shown in figure 19, the source should be capable of greater than 1.3a of output current. the source requirements are critical because if violated, proper termination of the fast- charge cycle might not occur. for input voltages greater than 15v, see the MAX713swevkit data sheet. 0.022 f 0.022 f note: for absolute temperature charge cutoff, t2 and t3 can be replaced by standard resistors. 1 f temp tlo in thermal contact with battery ambient temperature ambient temperature t3 +2.0v t2 t1 r3 r4 r5 hot ref thi batt- cold max712 MAX713 figure 9a. temperature comparators max712 MAX713 0.022 f 0.022 f note: for absolute temperature charge cutoff, t2 and t3 can be replaced by standard resistors. 1 f temp tlo ambient temperature ambient temperature in thermal contact with battery t3 +2.0v t1 t2 r4 r3 r5 hot ref thi batt- cold figure 9b. alternative temperature comparator configuration 11 6 0 200 600 1000 7 10 max712/713 output voltage (v) 400 800 9 8 120hz ripple low peak high peak load current (ma) figure 10. sony radio ac adapter ac-190 load characteristic, 9vdc 800ma
max712/MAX713 nicd/nimh battery fast-charge controllers 14 ______________________________________________________________________________________ the voltage-slope, fast-charge termination circuitry might become disabled if attempting to charge a different number of cells than the number programmed. the switching frequency (nominally 30khz) can be decreased by increasing the value of the capacitor connected between cc and batt-. make sure that the two capacitors connected to the cc node are placed as close as possible to the cc pin on the max712/MAX713 and that their leads are of minimum length. the cc node is a high-impedance point, so do not route logic lines near the cc pin. the circuit of figure 19 cannot service a load while charging. order the MAX713swevkit-so for quick evaluation of the max712/MAX713 in switch-mode operation. for more information on switch-mode operation and ordering information for external components, order the MAX713evkit data sheet. battery-charging examples figures 13 and 14 show the results of charging 3 aa, 1000mah, nimh batteries from gold peak (part no. gp1000aah, gp batteries (619) 438-2202) at a 1a rate using the max712 and MAX713, respectively. the typical operating circuit is used with figure 9a? thermistor configuration . dc in = sony ac-190 +9vdc at 800ma ac-dc adapter pgm0 = v+, pgm1 = ref, pgm2 = ref, pgm3 = ref r1 = 200 ? , r2 = 150 ? , r sense = 0.25 ? c1 = 1 f, c2 = 0.01 f, c3 = 10 f, v limit = ref r3 = 10k ? , r4 = 15k ? t1, t2 = part #13a1002 (alpha thermistor: (800) 235-5445) r5 omitted, t3 omitted, tlo = batt- 11 6 5 0 200 600 1000 7 10 max712/713 output voltage (v) 400 800 9 8 low peak high peak 120hz ripple load current (ma) figure 11. sony cd player ac adapter ac-96n load characteristic, 9vdc 600ma 4.3 4.2 030 90 4.5 5.0 4.9 4.7 4.4 battery voltage (v) battery temperature ( c) 60 time (minutes) 4.8 4.6 ? v ? t cutoff 26 24 30 40 38 34 28 36 32 v t max712/713 figure 13. 3 nimh cells charged with max712 10 8 0 200 600 12 18 max712/713 output voltage (v) 400 load current (ma) 800 16 14 high peak low peak 120hz ripple figure 12. panasonic modem ac adapter kx-a11 load characteristic, 12vdc 500ma 4.3 4.2 030 90 4.5 5.0 4.9 4.7 4.4 max712/713 battery voltage (v) battery temperature ( c) 60 time (minutes) 4.8 4.6 26 24 30 40 38 34 28 36 32 ? v ? t cutoff v t figure 14. nimh cells charged with MAX713
max712/MAX713 nicd/nimh battery fast-charge controllers ______________________________________________________________________________________ 15 linear-mode, high series cell count the absolute maximum voltage rating for the batt+ pin is higher when the max712/MAX713 are powered on. if more than 11 cells are used in the battery, the batt+ input voltage must be limited by external circuitry when dc in is not applied (figure 15). efficiency during discharge the current-sense resistor, r sense , causes a small efficiency loss during battery use. the efficiency loss is significant only if r sense is much greater than the battery stack? internal resistance. the circuit in figure 16 can be used to shunt the sense resistor whenever power is removed from the charger. status outputs figure 17 shows a circuit that can be used to indicate charger status with logic levels. figure 18 shows a circuit that can be used to drive leds for power and charger status. q1 d1 r2 150 ? dc in 33k ? q2 500 ? drv batt+ to battery positive terminal max712 MAX713 figure 15. cascoding to accommodate high cell counts for linear-mode circuits 100k ? d1 v+ gnd r sense >4 cells low r on logic level n-channel power mosfet * * max712 MAX713 100k ? figure 16. shunting r sense for efficiency improvement v cc ov = no power 5v = power ov = fast v cc = trickle or no power max712 MAX713 v+ fastchg 10k ? figure 17. logic-level status outputs v+ r1 470 ? min fastchg dc in charge power fast charge max712 MAX713 figure 18. led connection for status outputs
max712/MAX713 nicd/nimh battery fast-charge controllers 16 ______________________________________________________________________________________ dc in batt + batt 8v to 15v c5 10 f 50v c1 1 f 10v c3 10 f 50v c4 0.1 f 220 h q4 cmpta06 d4 cclhm080 (8ma current- limiting diode) c6 10 f 50v r2 5.1k ? 3 3 1 1 2 3 1 14 drv cc v+ thi batt+ batt- tld pgm3 2 x 1000ma-hr nicd cells pgm2 pgm1 pgm0 MAX713 ref gnd vlimit temp 5 15 3 2 4 12 13 6 8 9 10 16 1 7 ref r5 470 ? r6 68k ? r7 22k ? r3 0.25 ? 11 2 2 q1 cmpta06 q2 2n2907 d2 mbrs340t3 c2 220pf d1 mbrs340t3 m1 irfr9024 l1 d03340 fastchg figure 19. simplest switch-mode charger
maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 17 __________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 (408) 737-7600 2001 maxim integrated products printed usa is a registered trademark of maxim integrated products. ordering information (continued) ___________________chip topography drv thi tlo pgm3 0.126 (3.200mm) 0.80" (2.032mm) temp fastchg pgm2 gnd batt- cc batt+ vlimit ref v+ pgm1 pgm0 part MAX713 cpe MAX713cse MAX713c/d 0? to +70? 0? to +70? 0? to +70? temp. range pin-package 16 plastic dip 16 narrow so dice* MAX713epe MAX713ese MAX713mje -55? to +125? -40? to +85? -40? to +85? 16 plastic dip 16 narrow so 16 cerdip** transistor count: 2193 substrate connected to v+ * contact factory for dice specifications. ** contact factory for availability and processing to mil-std-883.

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