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| 1 features ? provides accurate measurement of available charge in nicd, nimh, and li-ion batteries ? supports sbs v1.0 data set and two-wire interface ? monitors charge fet in li-ion pack protection circuit ? designed for battery pack inte - gration - low operating current - complete circuit can fit on less than ? square inch of pcb space ? supports sbs charge control commands for nicd, nimh, and li-ion ? drives a four-segment led dis- play for remaining capacity indication ? 16-pin narrow soic general description the bq2040 gas gauge ic with smbus interface is intended for battery-pack or in-system installa - tion to maintain an accurate record of available battery charge. the bq2040 directly supports capacity monitoring for nicd, nimh, and li- ion battery chemistries. the bq2040 uses the system man - agement bus v1.0 (smbus) protocol and supports the smart battery data (sbdata) commands. the bq2040 also supports the sbdata charge control functions. battery state-of-charge, remaining capacity, remaining time, and chemistry are available over the serial link. battery-charge state can be directly indicated using a four-segment led display to graphically depict battery full-to-empty in 25% increments. the bq2040 estimates battery self- discharge based on an internal timer and temperature sensor and user-programmable rate informa - tion stored in external eeprom. the bq2040 also automatically re - calibrates or ?learns? battery capac - ity in the full course of a discharge cycle from full to empty. the bq2040 may operate directly from three nickel chemistry cells. with the ref output and an exter - nal transistor, a simple, inexpensive regulator can be built to provide v cc for other battery cell configu - rations. an external eeprom is used to program initial values into the bq2040 and is necessary for proper operation. bq2040 gas gauge ic with smbus interface v cc 3.0?6.5v escl eeprom clock esda eeprom data led 1-4 led segment 1-4 v ss system ground sr sense resistor input disp display control input 1 pn204001.eps 16-pin narrow soic 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 v cc escl esda led 1 led 2 led 3 led 4 v ss v out ref smbc smbd pstat sb disp sr sb battery sense input pstat protector status input smbd smbus data input/output smbc smbus clock ref voltage reference output v out eeprom supply output 6/99 e pin connections pin names
pin descriptions v cc supply voltage input escl serial memory clock output used to clock the data transfer be - tween the bq2040 and the external non - volatile configuration memory. esda serial memory data and address bidirectional pin used to transfer address and data to and from the bq2040 and the ex - ternal nonvolitile configuration memory. led 1 ? led 4 led display segment outputs each output may drive an external led. v ss ground sr sense resistor input the voltage drop (v sr ) across pins sr and v ss is monitored and integrated over time to interpret charge and discharge activity. the sr input is connected to the sense re- sistor and the negative terminal of the battery. v sr functional description general operation the bq2040 determines battery capacity by monitoring the amount of charge put into or removed from a re - chargeable battery. the bq2040 measures discharge and charge currents, estimates self-discharge, and monitors the battery for low-battery voltage thresholds. the charge is measured by monitoring the voltage across a small-value series sense resistor between the battery's negative terminal and ground. the available battery charge is determined by monitoring this voltage over time and correcting the measurement for the envi - ronmental and operating conditions. figure 1 shows a typical battery pack application of the bq2040 using the led capacity display, the serial port, and an external eeprom for battery pack program - ming information. the bq2040 must be configured and calibrated for the battery-specific information to ensure proper operation. table 1 outlines the configuration in - formation that must be programmed in the eeprom. an internal temperature sensor eliminates the need for an external thermistor?reducing cost and compo - nents. an internal, temperature-compensated time- base eliminates the need for an external resonator, further reducing cost and components. the entire cir - cuit in figure 1 can occupy less than 3 4 square inch of board space. 3 bq2040 v cc v out ref smbc smbd p s tat sb sr disp escl esda led1 led2 led3 led4 bq2040 v ss 2040led.eps 301k bss138 100k 100k 100k 100k 100k 100k 100k 86.5k 604k 806k 604k 499k 806k 499k 604k 909k bss138 bss138 2n7002 bss138 2n7002 2n7002 2n7002 2 r5 r4 q1 r11 no. of cells chart 1 for bq2040 with no d8 li-ion nimh 3 4 6 8 9 10 12 499k 499k 698k 698k 806k 909k 909k (optional) (optional) figure 1. battery pack application diagram?led display 4 bq2040 parameter name address description length units eeprom length 0x00 number of eeprom data locations must = 0x64 8 bits na eeprom check1 0x01 eeprom data integrity check byte, must = 0x5b 8 bits na remaining time alarm 0x02/0x03 sets remainingtimealarm (0x02) 16 bits minutes remaining capacity alarm 0x04/0x05 sets remainingcapacityalarm (0x01) 16 bits mah reserved 0x06/0x07 reserved for future use 16 bits na initial charging current 0x08/0x09 sets the initial charging current 16 bits ma charging voltage 0x0a/0x0b sets chargingvoltage (0x15) 16 bits mv battery status 0x0c/0x0d initializes batterystatus (0x16) 16 bits na cycle count 0x0e/0x0f initializes and stores cyclecount (0x17) 16 bits cycles design capacity 0x10/0x11 sets designcapacity (0x18) 16 bits mah design voltage 0x12/0x13 sets designvoltage (0x19) 16 bits mv specification information 0x14/0x15 programs specificationinfo (0x1a) 16 bits na manufacture date 0x16/0x17 programs manufacturedate (0x1b) 16 bits na serial number 0x18/0x19 programs serialnumber (0x1c) 16 bits na fast-charging current 0x1a/0x1b sets chargingcurrent (0x14) 16 bits ma maintenance-charge current 0x1c/0x1d sets the trickle current request 16 bits ma reserved 0x1e/0x1f reserved must = 0x0000 16 bits mah manufacturer name 0x20-0x2b programs manufacturername (0x20) 96 bits na current overload 0x2c/0x2d sets the overload current threshold 16 bits ma battery low % 0x2e sets the battery low amount 8 bits % reserved 0x2f reserved for future use 8 bits na device name 0x30-0x37 programs devicename (0x21) 64 bits na li-ion taper current 0x38/0x39 sets the upper limit of the taper current for charge termination 16 bits ma maximum overcharge limit 0x3a/0x3b sets the maximum amount of overcharge 16 bits na reserved 0x3c reserved must = 0x00 8 bits na access protect 0x3d locks commands outside of the sbs data set 8 bits na flags1 0x3e initializes flags1 8 bits na flags2 0x3f initializes flags2 8 bits na device chemistry 0x40-0x45 programs devicechemistry (0x22) 48 bits na current measurement gain 0x46/0x47 sense resistor calibration value 16 bits na battery voltage offset 0x48 voltage calibration value 8 bits na temperature offset 0x49 temperature calibration value 8 bits na maximum temperature and ? t step 0x4a sets the maximum charge temperature and the ? t step for ? t/ ? t termination 8 bits na table 1. configuration memory map 5 bq2040 parameter name address description length units charge efficiency 0x4b sets the high/low charge rate efficiencies 8 bits na full charge percentage 0x4c sets the percent at which the battery is consid - ered fully charged 8 bits na digitial filter 0x4d sets the minimum charge/discharge threshold 8 bits na current integration gain 0x4e programs the current integration gain to the sense resistor value 8 bits na self-discharge rate 0x4f sets the battery?s self-discharge rate 8 bits na manufacturer data 0x50-0x55 programs manufacturerdata (0x23) 48 bits na voltage gain1 0x56/0x57 battery divider calibration value 16 bits na reserved 0x58-0x59 reserved 16 bits na edvf charging current 0x5a/0x5b sets the charge current request when the battery voltage is less than edvf 16 bits na end of discharge voltage1 0x5c/0x5d sets edv1 16 bits na end of discharge voltage final 0x5e/0x5f sets edvf 16 bits na full-charge capacity 0x60/0x61 initializes and stores fullchargecapacity (0x10) 16 bits mah ? t step 0x62 sets the ? t step for ? t/ ? t termination 8 bits na hold-off time 0x63 sets ? t/ ? t hold-off timer 8 bits na eeprom check 2 0x64 eeprom data integrity check byte must = 0xb5 8 bits na reserved 0x65-0x7f reserved for future use na table 1. configuration memory map (continued) voltage thresholds in conjunction with monitoring v sr for charge/discharge currents, the bq2040 monitors the battery potential through the sb pin. the voltage potential is deter - mined through a resistor-divider network per the fol - lowing equation: r r mbv 2.25 5 4 1 =? where mbv is the maximum battery voltage, r 5 is con - nected to the positive battery terminal, and r 4 is con - nected to the negative battery terminal. r 5 /r 4 should be rounded to the next higher integer. the voltage at the sb pin (v sb ) should never exceed 2.4v. the battery voltage is monitored for the end-of- discharge voltages (edv1 and edvf) and for alarm warning conditions. edv threshold levels are used to de - termine when the battery has reached a programmable ?empty? state. the bq2040 generates an alarm warning when the battery voltage exceeds the maximum charg - ing voltage by 5% or if the voltage is below edvf. the battery voltage gain, the two edv thresholds, and the charging voltage are programmable in the eeprom. if v sb is below either of the two edv thresholds, the associ- ated flag is latched and remains latched, independent of v sb , until the next valid charge. edv monitoring may be disabled under certain condi- tions. if the discharge current is greater than the value stored in location 0x2c and 0x2d in the eeprom (ee 0x2c/0x2d), edv monitoring is disabled and resumes af- ter the current falls below the programmed value. reset the bq2040 is reset when first connected to the battery pack. on power-up, the bq2040 initializes and reads the eeprom configuration memory. the bq2040 can also be reset with a command over the smbus. the software reset sequence is the following: (1) write maxerror (0x0c) to 0x0000; (2) write the reset register (0x64) to 0x8009. a software reset can only be performed if the bq2040 is in an unlocked state as defined by the value in location 0x3d of the eeprom (ee 0x3d) on power-up. temperature the bq2040 monitors temperature sensing using an in - ternal sensor. the temperature is used to adapt charge and self-discharge compensations as well as to monitor for maximum temperature and ? t/ ? t during a bq2040 controlled charge. temperature may also be accessed over the smbus with command 0x08. layout considerations the bq2040 measures the voltage differential between the sr and v ss pins. v os (the offset voltage at the sr pin) is greatly affected by pc board layout. for optimal results, the pc board layout should follow the strict rule of a single-point ground return. sharing high-current ground with small signal ground causes undesirable noise on the small signal nodes. additionally, in refer - ence to figure 1: the capacitors (c1 and c2) should be placed as close as possible to the sb and v cc pins, and their paths to v ss should be as short as possible. a high-quality ceramic capacitor of 0.1 f is recommended for v cc . the sense resistor capacitor (c3) should be placed as close as possible to the sr pin. the bq2040 should be in thermal contact with the cells for optimum temperature measurement. gas gauge operation the operational overview diagram in figure 2 illus- trates the operation of the bq2040. the bq2040 accumu- lates a measure of charge and discharge currents, as well as an estimation of self-discharge. charge currents are compensated for temperature and state-of-charge of the battery. self-discharge is temperature-compensated. the main counter, remainingcapacity (rm), represents the available battery capacity at any given time. battery charging increments the rm register, whereas battery dis- charging and self-discharge decrement the rm register and increment the internal discharge count register (dcr). the discharge count register is used to update the fullchargecapacity (fcc) register only if a complete battery discharge from full to empty occurs without any partial battery charges. therefore, the bq2040 adapts its capacity determination based on the actual condi - tions of discharge. the battery's initial full capacity is set to the value stored in ee 0x60-0x61. until fcc is updated, rm counts up to, but not beyond, this threshold during subsequent charges. the battery?s empty state is also programmed in the eeprom. the battery low percentage (ee 0x2e) stores the percentage of fcc that will be written to rm when the battery voltage drops below the edv1 threshold. 1. fullchargecapacity or learned-battery capacity: fcc is the last measured discharge capacity of the battery. on initialization (application of v cc or reset), fcc is set to the value stored in the eeprom. dur - 6 bq2040 ing subsequent discharges, fcc is updated with the latest measured capacity in the discharge count reg- ister plus the battery low amount, representing a dis- charge from full to below edv1. a qualified dis- charge is necessary for a capacity transfer from the dcr to the fcc register. once updated, the bq2040 writes the new fcc to the eeprom. the fcc also serves as the 100% reference threshold used by the relative state-of-charge calculation and display. 2. designcapacity (dc): the dc is the user-specified battery capacity and is programmed from external eeprom. the dc also provides the 100% reference for the absolute dis - play mode. 3. remainingcapacity (rm): rm counts up during charge to a maximum value of fcc and down during discharge and self-discharge to 0. rm is set to the battery low amount after the edv1 threshold has been reached. if rm is already equal to or less than the battery low amount, rm is not modified. if rm reaches the battery low amount before the battery voltage falls below edv1 on dis - charge, rm stops counting down until the edv1 threshold is reached. rm is set to 0 when the battery voltage reaches edvf. to prevent overstatement of charge during periods of overcharge, rm stops in - crementing when rm = fcc. rm may optionally be written to a user-defined value when fully charged if the battery pack is under bq2040 charge control. on initialization, rm is set to 0. 4. discharge count register (dcr): the dcr counts up during discharge independent of rm and can continue increasing after rm has decremented to 0. prior to rm = 0, both discharge and self-discharge incre ment the dcr. after rm = 0, only discharge in crements the dcr. the dcr resets to 0 when rm = fcc and stops counting at edv1 on discharge. the dcr does not roll over but stops counting when it reaches ffffh. fcc is updated on the first charge after a qualified discharge to edv1. the updated fcc equals the battery low percentage times the current fcc plus the dcr value. a qualified discharge to edv1 oc - curs if all of the following conditions exist: no valid charge initiations (charges greater than 10mah, where v sro >+v srd occurred during the period between rm = fcc and edv1 de - tected. the self-discharge count is not more than 256mah. the low temperature fault bit in flags2 is not set when the edv1 level is reached during dis - charge. battery voltage is not more than 256mv below the edv1 threshold when edv1 is set. the valid discharge flag (vdq) in flags1 indi - cates whether the present discharge is valid for an fcc update. fcc cannot be reduced by more than 256mah during any single cycle. 7 bq2040 fg294501.eps temperature compensation charge current discharge current self-discharge timer remaining capacity (rm) full charge capacity (fcc) discharge count register (dcr) < qualified transfer + temperature, other data + - - + inputs main counters and capacity reference (fcc) outputs two-wire serial interface chip-controlled available charge led display state-of-charge and temperature compensation figure 2. operational overview charge counting charge activity is detected based on a positive voltage on the sr input. if charge activity is detected, the bq2040 increments rm at a rate proportional to v sro and, if enabled, activates an led display. charge ac - tions increment the rm after compensation for charge state and temperature. the bq2040 determines charge activity sustained at a continuous rate equivalent to v sro >+v srd . a valid charge equates to sustained charge activity greater than 10 mah . once a valid charge is detected, charge threshold counting continues until v sro falls be - low v srd .v srd is a programmable threshold as de - scribed in the digital magnitude filter section. discharge counting all discharge counts where v sro <-v srd cause the rm register to decrement and the dcr to increment. v srd is a programmable threshold as described in the digital magnitude filter section. self-discharge estimation the bq2040 continuously decrements rm and incre- ments dcr for self-discharge based on time and temper- ature provided that the discharge flag in batterystatus is set (charge not detected). the bq2040 self-discharge estimation rate is programmed in ee 0x4f and can be set from 0 to 25% per day for 20?30c. this rate approx- imately doubles for every 10c increase until the tem- perature is 70 c or halves every 10 c decrease until the temperature is < 10 c. charge control the bq2040 supports sbs charge control by broadcast - ing the chargingcurrent and the chargingvoltage to the smart charger address. the bq2040 broadcasts charging commands every 10 seconds; the broadcasts can be disabled by writing bit 14 of batterymode to 1. on reset, the initial charging current broadcast to the charger is set to the value programmed in ee 0x08- 0x09. the bq2040 updates the value used in the charg - ing current broadcasts based on the battery?s state of charge, voltage, and temperature. the bq2040 internal charge control is compatible with nickel-based and li-ion chemistries. the bq2040 uses current taper detection for li-ion primary charge termi - nation and ? t/ ? t for nickel based primary charge termi - nation. the bq2040 also provides a number of safety terminations based on battery capacity, voltage, and temperature. current taper for li-ion charge control, the chargingvoltage must be set to the desired pack voltage during the constant volt - age charge phase. the bq2040 detects a current taper termination when it measures the pack voltage to be within 128mv of the requested charging voltage and when the averagecurrent is less than the programmed threshold in ee 0x38?0x39 and non-zero for at least 100s. ? t/ ? t the ? t/ ? t used by the bq2040 is programmable in both the temperature step (1.6 c?4.6 c) and time step (20 seconds?320seconds). typical settings for 1 c/min in - clude 2 c over 120 seconds and 3 c over 180 seconds. longer times are required for increased slope resolution. ? ? t t is set by the formula: ? ? t t = [] [( (lower nibble of ee 0x4a) 2 + 16 / 10 ee 0x62 ? ? 320 ) 20)] c s ? ? ? ? ? ? ? o in addition to the ? t/ ? t timer, there is a hold-off timer, which starts when the battery is being charged at more than 255ma and the temperature is above 25 c. until this timer expires, ? t/ ? t is suspended. if the tempera- ture falls below 25 c, or if charging current falls below 255ma, the timer is reset and restarts only if these con- ditions are once again within range. the hold-off time is programmed in ee 0x63. charge termination once the bq2040 detects a valid charge termination, the fully_charged, terminate_charge_alarm, and the over_charged_alarm bits are set in batterystatus, and the requested charge current is set to zero. once the terminating conditions cease, the termi - nate_charge_alarm and the over_charged_alarm are cleared, and the requested charging current is set to the maintenance rate. the bq2040 requests the mainte - nance rate until rm falls below the amount determined by the programmable full- charge percentage. once this occurs, the fully_charged bit is cleared, and the re - quested charge current and voltage are set to the fast-charge rate. bit 4 (cc) in flags2 determines whether rm is modi - fied after a ? t/ ? t or current taper termination occurs. if cc = 1, rm may be set from 0 to 100% of the fullchar - gecapacity as defined in ee 0x4c. if rm is below the full-charge percentage, rm is set to the full-charge per - centage of fcc. if rm is above the full-charge percent - age, rm is not modified. 8 bq2040 charge suspension the bq2040 may temporarily suspend charge if it detects a charging fault. the charging faults include the follow - ing conditions: maximum overcharge: if charging continues for more than the programmed maximum overcharge limit as defined in ee 0x3a?0x3b beyond rm=fcc, the fully_charged bit is set, and the requested charging current is set to the maintenance rate. overvoltage: an over-voltage fault exists when the bq2040 measures a voltage more than 5% above the chargingvoltage. when the bq2040 detects an overvoltage condition, the requested charge current is set to 0 and the terminate_charge_alarm bit is set in batterystatus. the alarm bit is cleared when the current drops below 256ma and the voltage is less than 105% of chargingvoltage. overcurrent: an overcurrent fault exists when the bq2040 measures a charge current more than 25% above the chargingcurrent. if the chargingcurrent is less than 1024ma, an overcurrent fault exists if the charge current is more than 1ma above the lowest multiple of 256ma that exceeds the chargingcurrent. when the bq2040 detects an overcurrent condition, the requested charge current is set to 0 and the terminate_charge_alarm bit is set in battery status. the alarm bit is cleared when the current drops below 256ma. maximum temperature : when the battery temperature equals the programmed maximum temperature, the requested charge current is set to zero and the over_temp_alarm and the terminate_charge_alarm bits are set in battery status. the over_temp_alarm bit is cleared when the temperature drops to 43c below the maximum temperature threshold minus 5 c. pstat: when the pstat input is 1.5v, the requested charge current is set to 0 and the terminate_charge_alarm bit is set in batterystatus if the discharging flag is not set. the alarm bit is cleared when the pstat input is <1.0v or the discharging flag is set. low temperature: when the battery temperature is less than 12c (ltf bit in flags2 set), the requested charge current is set to the maintenance rate. once the temperature is above 15 c, the requested charge current is set to the fast rate. undervoltage: when the battery voltage is below the edvf threshold, the requested charge current is set to the edvf rate stored in ee0x5a/0x5b. once the voltage is above edvf, the requested charge current is set to the fast or maintenance rate depending on the state of the ltf bit. count compensations charge activity is compensated for temperature and state-of-charge before updating the rm and/or dcr. self-discharge estimation is compensated for tempera - ture before updating rm or dcr. charge compensation charge efficiency is compensated for state-of-charge, temperature, and battery chemistry. the charge effi - ciency is adjusted using the following equations: 1.) rm rm * q q efc et =? () where relativestateofcharge < fullchargepercentage, and q efc is the programmed fast-charge efficiency vary - ing from 0.75 to 1.0. 2.) rm rm q q etc et =? *( ) where relativestateofcharge fullchargepercentage and q etc is the programmed maintenance (trickle) charge efficiency varying from 0.75 to 1.0. q et is used to adjust the charge efficiency as the battery temperature increases according to the following: qift et =< 030 c qctc et =< 002 30 40 .if qtc et =? 005 40 .if q et is 0 over the entire temperature range for li-ion. digital magnitude filter the bq2040 has a programmable digital filter to elimi - nate charge and discharge counting below a set threshold, v srd . table 2 shows typical digital filter settings. the proper digital filter setting can be calcu - lated using the following equation. dmf = 45 v srd 9 bq2040 dmf dmf hex. v srd (mv) 75 4b 0.60 100 64 0.45 150 96 0.30 175 af 0.26 200 c8 0.23 table 2. typical digital filter settings error summary capacity inaccurate the fcc is susceptible to error on initialization or if no updates occur. on initialization, the fcc value includes the error between the design capacity and the actual ca - pacity. this error is present until a qualified discharge occurs and fcc is updated (see the dcr description). the other cause of fcc error is battery wear-out. as the battery ages, the measured capacity must be adjusted to account for changes in actual battery capacity. periodic qualified discharges from full to empty will minimize er- rors in fcc. current-sensing error table 3 illustrates the current-sensing error as a func- tion of v sr . a digital filter eliminates charge and dis- charge counts to the rm register when -v srd 12 bq2040 function code access units defaults 1 manufactureraccess 0x00 read/write - - remaningcapacityalarm 0x01 read/write mah e 2 remainingtimealarm 0x02 read/write minutes e 2 batterymode 0x03 read/write bit flag - atrate 0x04 read/write ma - atratetimetofull 0x05 read minutes - atratetimetoempty 0x06 read minutes - atrateok 0x07 read boolean - temperature 0x08 read 0.1k 2930 voltage 0x09 read mv e 2 current 0x0a read ma 0 averagecurrent 0x0b read ma 0 maxerror 0x0c read percent 100 relativestateofcharge 0x0d read percent - absolutestateofcharge 0x0e read percent - remainingcapacity 0x0f read mah e 2 fullchargecapacity 0x10 read mah e 2 runtimetoempty 0x11 read minutes - averagetimetoempty 0x12 read minutes - averagetimetofull 0x13 read minutes - chargingcurrent 0x14 read ma e 2 chargingvoltage 0x15 read mv e 2 battery status 0x16 read bit flags e 2 cyclecount 0x17 read cycle e 2 designcapacity 0x18 read mah e 2 designvoltage 0x19 read mv e 2 specificationinfo 0x1a read - e 2 manufacturedate 0x1b read - e 2 serialnumber 0x1c read integer e 2 reserved 0x1d - 0x1f - - - manufacturername 0x20 read string e 2 devicename 0x21 read string e 2 note: 1. defaults after reset or power-up. table 4. bq2040 register functions 13 bq2040 function code access units defaults 1 devicechemistry 0x22 read string e 2 manufacturerdata 0x23 read string e 2 flag1 and flag2 0x2f read bit flags e 2 end of discharge voltage 1 (edv1) 0x3e read - e 2 end of discharge voltage final (edvf) 0x3f read - e 2 note: 1. defaults after reset or power-up. table 4. bq2040 register functions (continued) when the atrate value is positive, the atratetimetofull function returns the predicted time to full-charge at the atrate value of charge. when the atrate value is negative, the atratetimetoempty function returns the predicted operating time at the atrate value of discharge. input/output: signed integer. atrate is positive for charge and negative for discharge. units: ma range: -32,768ma to 32,767ma atratetimetofull() (0x05) this read-only word returns the predicted remaining time to fully charge the battery at the atrate value (ma) and is valid only if read immediately after an atrate command. output: unsigned integer. returns the predicted time to full charge. units: minutes range: 0 to 65,534min granularity: 2 min or better invalid data indication: 65,535 indicates that the atrate value is negative. atratetimetoempty() (0x06) this read-only word returns the predicted remaining op- erating time if the battery is discharged at the atrate value and is valid only if read immediately after an atrate command. output: unsigned integer. returns the predicted time to empty. units: minutes range: 0 to 65,534min granularity: 2min or better invalid data indication: 65,535 indicates that the atrate value is not negative. atrateok() (0x07) this read-only word returns a boolean value that indi - cates whether or not the edvf flag has been set. boolean: indicates if the battery can supply addi - tional energy. units: boolean range: true 0, false = 0 temperature() (0x08) this read-only word returns the cell-pack's internal temperature. output: unsigned integer. returns the cell tem - perature in tenths of degrees kelvin increments. units: 0.1k range: 0 to +500.0k granularity: 0.5k or better accuracy: 3k after calibration voltage() (0x09) this read-only word returns the cell-pack voltage (mv). output: unsigned integer. returns the battery ter - minal voltage in mv. units: mv range: 0 to 65,535mv granularity: 0.2% of designvoltage accuracy: 1% of designvoltage after calibration current() (0x0a) this read-only word returns the current through the battery's terminals (ma). output: signed integer. returns the charge/dis- charge rate in ma, where positive is for charge and negative is for discharge units: ma range: 0 to 32,767ma for charge or 0 to ?32,768ma for discharge granularity: 0.2% of the designcapacity or better accuracy: 1% of the designcapacity after calibration averagecurrent() (0x0b) this read-only word returns a rolling average of the cur - rent through the battery's terminals. the averagecur - rent function returns meaningful values after the bat - tery's first minute of operation. output: signed integer. returns the charge/dis - charge rate in ma, where positive is for charge and negative is for discharge units: ma range: 0 to 32,767ma for charge or 0 to ?32,768ma for discharge granularity: 0.2% of the designcapacity or better 14 bq2040 accuracy: 1% of the designcapacity after cali - bration maxerror() (0x0c) returns the expected margin of error (%) in the state of charge calculation. output: unsigned integer. returns the percent un - certainty for selected information. units: % range: 0 to 100% relativestateofcharge() (0x0d) this read-only word returns the predicted remaining battery capacity expressed as a percentage of fullchar - gecapacity (%). relativestateofcharge is only valid for battery capacities more than 1504mah and less than 10,400mah. output: unsigned integer. returns the percent of re - maining capacity. units: % range: 0 to 100% granularity: 1% accuracy: maxerror after circuit and capacity calibration absolutestateofcharge() (0x0e) this read-only word returns the predicted remaining battery capacity expressed as a percentage of designca - pacity (%). note that absolutestateofcharge can return values greater than 100%. absolute stateofcharge is only valid for battery capacities more than 1504mah and less than 10,400mah . output: unsigned integer. returns the percent of remaining capacity. units: % range: 0 to 65,535% granularity: 1% accuracy: maxerror after circuit and capacity calibration remainingcapacity() (0x0f) this read-only word returns the predicted remaining battery capacity. the remainingcapacity value is ex - pressed in mah. output: unsigned integer. returns the estimated re - maining capacity in mah. units: mah range: 0 to 65,535mah granularity: 0.2% of designcapacity or better accuracy: maxerror ? fcc after circuit and ca - pacity calibration fullchargecapacity() (0x10) this read-only word returns the predicted pack capacity when it is fully charged. fullchargecapacity defaults to the value programmed in the external eeprom until a new pack capacity is learned. the new fcc is stored to eeprom within 400ms of a valid charge after a qualified discharge. output: unsigned integer. returns the estimated full charge capacity in mah. units: mah range: 0 to 65,535mah granularity: 0.2% of designcapacity or better accuracy: maxerror ? fcc after circuit and ca- pacity calibration runtimetoempty() (0x11) this read-only word returns the predicted remaining battery life at the present rate of discharge (minutes). the runtimetoempty value is calculated based on current. output: unsigned integer. returns the minutes of operation left. units: minutes range: 0 to 65,534min granularity: 2min or better invalid data indication: 65,535 indicates battery is not being discharged. averagetimetoempty() (0x12) this read-only word returns the predicted remaining battery life at the present average discharge rate (min - utes). the averagetimetoempty is calculated based on averagecurrent. 15 bq2040 output: unsigned integer. returns the minutes of operation left. units: minutes range: 0 to 65,534min granularity: 2min or better invalid data indication: 65,535 indicates battery is not being discharged. averagetimetofull() (0x13) this read-only word returns the predicted time until the smart battery reaches full charge at the present aver - age charge rate (minutes). output: unsigned integer. returns the remaining time in minutes to full. units: minutes range: 0 to 65,534min granularity: 2min or better invalid data indication: 65,535 indicates battery is not being charged. chargingcurrent() (0x14) if enabled, the bq2040 sends the desired charging rate in ma to the smart battery charger. output: unsigned integer. transmits/returns the maximum charger output current in ma. units: ma range: 0 to 65,534ma granularity: 0.2% of the design capacity or better invalid data indication: 65,535 indicates that the smart charger should operate as a voltage source outside its maximum regulated current range. chargingvoltage() (0x15) if enabled, the bq2040 sends the desired voltage in mv to the smart battery charger. output: unsigned integer. transmits/returns the charger voltage output in mv. units: mv range: 0 to 65,534mv granularity: 0.2% of the designvoltage or better invalid data indication: 65,535 indicates that the smart battery charger should operate as a cur - rent source outside its maximum regulated voltage range. batterystatus() (0x16) this read-only word returns the battery status word. output: unsigned integer. returns the status reg - ister with alarm conditions bitmapped as shown in table 5. some of the batterystatus flags (remaining_capac - ity_alarm and remaining_time_alarm) are calculated based on current. see table 8 and 9 for definitions. cyclecount() (0x17) this read-only word returns the number of charge/dis - charge cycles the battery has experienced. a charge/dis - charge cycle starts from a base value equivalent to the battery's state-of-charge on completion of a charge cycle. the bq2040 increments the cycle counter during the cur - rent charge cycle if the battery has been discharged 15% below the state-of-charge at the end of the last charge cy - cle. this prevents false reporting of small charge/discharge cycles. the cycle count is stored in eeprom within 400ms of an update. output: unsigned integer. returns the count of charge/discharge cycles the battery has experienced. units: cycles 16 bq2040 alarm bits 0x8000 over_charged_alarm 0x4000 terminate_charge_alarm 0x2000 reserved 0x1000 over_temp_alarm 0x0800 terminate_discharge_alarm 0x0400 reserved 0x0200 remaining_capacity_alarm 0x0100 remaining_time_alarm status bits 0x0080 initialized 0x0040 discharging 0x0020 fully_charged 0x0010 fully_discharged error code 0x0000- 0x000f reserved for error codes table 5. status register range: 0 to 65,535 cycles; 65,535 indicates battery has experienced 65,535 or more cycles. granularity: 1 cycle designcapacity() (0x18) this read-only word returns the theoretical capacity of a new pack. the designcapacity value is expressed in mah at the nominal discharge rate. output: unsigned integer. returns the battery ca - pacity in mah. units: mah range: 0 to 65,535mah designvoltage() (0x19) this read-only word returns the theoretical voltage of a new pack in mv. output: unsigned integer. returns the battery's normal terminal voltage in mv. units: mv range: 0 to 65,535mv specificationinfo() (0x1a) this read-only word returns the specification re - vision the bq2040 supports. manufacturedate() (0x1b) this read-only word returns the date the cell was manu - factured in a packed integer word. the date is packed as follows: (year - 1980) ? 512 + month ? 32+day. serialnumber() (0x1c) this read-only word returns a serial number. this number, when combined with the manufacturername, the devicename, and the manufacturedate, uniquely identifies the battery. output: unsigned integer manufacturername() (0x20) this read-only string returns a character string where the first byte is the number of characters available. the maxi- mum number of characters is 11. the character string con- tains the battery manufacturer's name. for example, ?benchmarq? identifies the battery pack manufacturer as benchmarq. output: string or ascii character string devicename() (0x21) this read-only string returns a character string where the first byte is the number of characters available. the maxi- mum number of characters is 7. the 7-byte character string contains the battery's name. for example, a devicename of ?bq2040? indicates that the battery is a model bq2040. output: string or ascii character string devicechemistry() (0x22) this read-only string returns a character string where the first byte is the number of characters available. the maximum number of characters is 5. the 5-byte charac - ter string contains the battery's chemistry. for example, if the devicechemistry function returns ?nimh,? the battery pack contains nickel-metal hydride cells. output: string or ascii character string manufacturerdata() (0x23) this read-only string allows access to an up to 5-byte manufacturer data string. output: block data?data whose meaning is as - signed by the smart battery's manufacturer. 17 bq2040 (msb) 7 6543210 (lsb) flags2 dmode pstat chm cc - ov ltf oc flags1 ? t/ ? t i min vq - vdq ovld edv1 edvf note: - = reserved table 6. bit descriptions for flags1 and flags2 field bits used format allowable value day 0?4 5-bit binary value 1?31 (corresponds to date) month 5?8 4-bit binary value 1?12 (corresponds to month number) year 9?15 7-bit binary value 0?127 (corresponds to year biased by 1980) end of discharge voltage1 (0x3e) this read-only word returns the first end-of-discharge voltage programmed for the pack. output: two?s complemented unsigned integer. returns battery end-of-discharge voltage pro - grammed in eeprom in mv. end of discharge voltagef (0x3f) this read-only word returns the final end-of-discharge voltage programmed for the pack. output: two?s complemented unsigned integer. returns battery final end-of-discharge voltage pro - grammed in eeprom in mv. flags1&2() (0x2f) this read-only register returns an unsigned integer rep - resenting the internal status registers of the bq2040. the msb represents flags2, and the lsb represents flags1. see table 6 for the bit description for flags1 and flags2. flags2 the display mode flag (dmode), bit 7 determines whether the bq2040 displays relative or absolute capac- ity. the dmode value is: where dmode is: 0 selects absolute display 1 selects relative display bit 6 reflects the high/low state of pstat. pstat 1.5v generates a charge suspend condition. the pstat value is: where pstat is: 0 pstat input < 1.0v 1 pstat input 1.5v the chemistry flag (chm), bit 5, selects li-ion or nickel compensation factors. the chm value is: where chm is: 0 selects nickel 1 selects li-ion bit 4, the charge control flag (cc), determines whether a bq2040-based charge termination will set rm to a user-defined programmable full charge capacity. the cc value is: where cc is: 0 rm is not modified on valid bq2040 charge termination 1 rm is set to a programmable percentage of the fcc when a valid bq2040 charge termi- nation occurs bit 3 is reserved. bit 2, the overvoltage flag (ov), is set when the bq2040 detects a pack voltage 5% greater than the programmed charging voltage. this bit is cleared when the pack volt - age falls 5% below the programmed charging voltage. the ov value is: where ov is: 0 voltage < 1.05 ? chargingvoltage 1 voltage 1.05 ? chargingvoltage bit 1, the low temperature fault flag (ltf), is set when temperature is < 12c and cleared when temperature is 15c. the ltf value is: 18 bq2040 flags2 bits 76 5 43210 - - - - -ov- - flags2 bits 76 5 43210 -- - cc---- flags2 bits 7 6543210 dmode ------- flags2 bits 76 5 43210 --chm----- flags2 bits 76 5 43210 -- - ---ltf- flags2 bits 7 6 543210 -pstat------ where ltf is: 0 temperature > 15c 1 temperature < 12c bit 0, the overcurrent flag (oc), is set when current is 25% greater than the programmed charging current. if the charging current is programmed less than 1024ma, overcurrent is set if current is 256ma greater than the programmed charging current. this flag is cleared when current falls below 256ma. the oc value is: where oc is: 0 current is less than 1.25 ? chargingcur - rent or less than 256ma if charging current is programmed less than 1024ma 1 current exceeds 1.25 ? chargingcurrent or 256ma if the charging current is pro- grammed less than 1024ma. this bit is cleared if current < 256ma. flags1 bits 7 indicates that a ? t/ ? t termination condition exists. the ? t/ ? t value is: where ? t/ ? t is: 0 the ? t/ ? t rate drops below the pro - grammed rate. 1 the ? t/ ? t rate exceeds the programmed rate. bit 6 indicates that a current taper termination condi - tion exists. the i min value is: where i min is: 0 a valid current taper termination condition is not present. 1 valid current taper termination condition detected. the valid charge flag (vq), bit 5, is set when v sro |v srd | and 10mah of charge has accumulated. this bit is cleared during a discharge and when v sro |v srd |. the vq value is: where vq is: 0v sro |v srd | 1v sro |v srd | and 10mah of charge has accumulated bit 4 is reserved. the valid discharge flag (vdq), bit 3, is set when a valid discharge is occurring (discharge cycle valid for learning new full charge capacity) and cleared if a par- tial charge is detected, edv1 is asserted whe n t < 0c, or self-discharge accounts for more than 256mah of the discharge. the vdq value is: where vdq is: 0 self-discharge is greater than 256mah, edv1 = 1 when t < 0c or vq = 1 1 on first discharge after rm=fcc the overload flag (ovld), bit 2, is set when the dis - charge current is greater than the programmed rate and cleared when the discharge current falls below the pro - grammed rate. 19 bq2040 flags1 bits 76543 2 10 - - - - - ovld - - flags1 bits 76 5 43210 -- vq ----- flags1 bits 7654 3 210 - - - - vdq - - - flags2 bits 765432 1 0 ------ - oc flags1 bits 7 6 5 43210 ? t/ ? t - - ----- flags1 bits 7 6 5 43210 -i min - ----- the ovld value is: where ovld is: 0 current < programmed rate 1 current > programmed rate the first end-of-discharge voltage flag (edv1), bit 1, is set when voltage < edv1 and ovl d = 0 and cleared when v q = 1 and voltage > edv1. the edv1 value is: where edv1 is: 0 vq = 1 and voltage > edv1 1 voltage < edv1 and ovld = 0 the final end-of-discharge voltage flag (edvf), bit 0, is set when voltage < edvf and ovl d = 0 and cleared when v q = 1 and voltage > edvf. the edvf value is: where edvf is: 0 vq = 1 and voltage > edvf 1 voltage < edvf and ovld = 0 error codes and status bits error codes and status bits are listed in table 8 and ta - ble 9, respectively. sbd seal the bq2040 address space can be ?locked? to enforce the sbs specified access to each command code. to lock the address space, the bq2040 must be initialized with ee 0x3d set to b0h. once this is done, only commands 0x00-0x04 may be written. attempting to write to any other address will cause a ?no acknowledge? of the data. reading will only be permitted from the command codes listed in the sbd specification plus the five locations designated as optional manufacturing functions 1?5 (0x2f, 0x3c?0x3f). programming the bq2040 the bq2040 requires the proper programming of an ex - ternal eeprom for proper device operation. each mod - ule can be calibrated for the greatest accuracy, or gen - eral ?default? values can be used. an ev2200-40 pro - gramming kit (interface board, software, and cable) for an ibm-compatible pc is available from benchmarq. the bq2040 uses a 24lc01 or equivalent serial ee- prom (capable of read operation to 2.0v) for storing the various initial values, calibration data, and string infor- mation. table 1 outlines the parameters and addresses for this information. tables 10 and 11 detail the various register contents and show an example program value for an 2400mah 4-series li-ion battery pack, using a 50m ? sense resistor. 20 bq2040 flags1 bits 765432 1 0 - - - - - - edv1 - flags1 bits 7654321 0 - - - - - - - edvf 21 bq2040 error code access description ok 0x0000 read/write bq2040 processed the function code without detecting any errors. busy 0x0001 read/write bq2040 is unable to process the function code at this time. reservedcommand 0x0002 read/write bq2040 cannot read or write the data at this time?try again later. unsupportedcommand 0x0003 read/write bq2040 does not support the requested function code. accessdenied 0x0004 write bq2040 detected an attempt to write to a read-only function code. overflow/underflow 0x0005 read/write bq2040 detected a data overflow or underflow. badsize 0x0006 write bq2040 detected an attempt to write to a function code with an incorrect size data block. unknownerror 0x0007 read/write bq2040 detected an unidentifiable error. note: reading the bq2040 after an error clears the error code. table 8. error codes (batterystatus() (0x16)) 22 bq2040 alarm bits bit name set when: reset when: over_charged_alarm the bq2040 detects a ? t/ ? t or cur - rent taper termination. ( note: ? t/ ? t and current taper are valid charge terminations .) a discharge occurs or when the ? t/ ? t or current taper termination condition ceases during charge. terminate_charge_alarm the bq2040 detects an over-current, over-voltage, over-temperature, ? t/ ? t, or current taper condition during charge. a discharge occurs or when all condi - tions causing the event cease. over_temp_alarm the bq2040 detects that its internal temperature is greater than the pro - grammed value. internal temperature falls to 43c or the maximum temperature threshold minus 5 c. terminate_discharge_alarm the bq2040 determines that it has supplied all the charge that it can without being damaged (voltage < edvf). voltage > edvf signifies that the battery has reached a state of charge sufficient for it to once again safely supply power. remaining_capacity_alarm the bq2040 detects that the remain- ingcapacity is less than that set by the remainingcapacityalarm func- tion. either the value set by the remain- ingcapacityalarm function is lower than the remaining capacity or the remainingcapacity is increased by charging. remaining_time_alarm the bq2040 detects that the esti- mated remaining time at the present discharge rate is less than that set by the remainingtimealarm func- tion. either the value set by the remain- ingtimealarm function is lower than the averagetimetoempty or a valid charge is detected. status bits bit name set when: reset when: initialized the bq2040 loads from the eeprom (bit 7 set in ee0x0c). a bad eeprom load is detected. discharging the bq2040 determines that it is not being charged. battery detects that it is being charged. fully_charged the bq2040 determines a valid charge termination or a maximum overcharge state. rm discharges below the full charge percentage. fully_discharged bq2040 determines that it has supplied all the charge that it can without being damaged. relativestateofcharge is greater than or equal to 20% table 9. batterystatus bits 23 bq2040 description eeprom address eeprom hex contents example values notes low byte high byte low byte high byte eeprom length 0x00 64 100 must be equal to 0x64. eeprom check 1 0x01 5b 91 must be equal to 0x5b. remaining time alarm 0x02 0x03 0a 00 10 minutes sets the low time alarm level. remaining capacity alarm 0x04 0x05 f0 00 240mah sets the low capacity alarm level. reserved 0x06 0x07 00 00 0 not currently used by the bq2040. initial charging current 0x08 0x09 60 09 2400ma sets the initial charge request. charging voltage 0x0a 0x0b d8 40 16600mv used to set the fast-charge voltage for the smart charger. battery status 0x0c 0x0d 80 00 128 initializes batterystatus. cycle count 0x0e 0x0f 00 00 0 contains the charge cycle count and can be set to zero for a new battery. design capacity 0x10 0x11 60 09 2400mah normal battery pack capacity. design voltage 0x12 0x13 40 38 14400mv nominal battery pack voltage. specification information 0x14 0x15 10 00 1.0 default value for this register in a 1.0 part. manufacture date 0x16 0x17 a1 20 may 1, 1996 = 8353 packed per the manufacturedate description. serial number 0x18 0x19 12 27 10002 contains the optional pack serial number. fast-charging current 0x1a 0x1b 60 09 2400ma used to set the fast-charge current for the smart charger. maintenance charge current 0x1c 0x1d 00 00 0ma contains the desired maintenance current after fast- charge termination by the bq2040. reserved 0x1e 0x1f 00 00 0 must be programmed to 0x00. current overload 0x2c 0x2d 70 17 6000ma sets the discharge current at which edv threshold monitoring is disabled. battery low % 0x2e 08 3% sets the battery capacity that remainingcapacity is reduced to at edv1. the value equals 2.56 ? (%rm at edv1) table 10. example register contents 24 bq2040 description eeprom address eeprom hex contents example values notes low byte high byte low byte high byte reserved 0x2f 00 0 not currently used by the bq2040. li-ion taper current 0x38 0x39 10 ff 240ma sets the upper taper limit for li-ion charge termina - tion. stored in 2?s complement. maximum overcharge limit 0x3a 0x3b 9c ff 100mah sets the maximum amount of overcharge before a maximum overcharge charge suspend occurs. stored in 2?s complement. reserved 0x3c 00 0 must be programmed to 0. access protect 0x3d b0 sbd access only if the bq2040 is reset and bit 3 of this location is 0, the bq2040 locks access to any command outside of the sbs data set. program to 0xb8 for full r/w access, 0xb0 for sbd access only. flags1 0x3e 00 0 initializes flags1 flags2 0x3f b0 relative display li-ion chemistry bq2040 charge control initializes flags2. current measurement gain 1 0x46 0x47 00 0f 3840 the current gain measurement and current integra- tion gain are related and defined for the bq2040 cur- rent measurement. this word equals 192/sense re- sistor value in ohms. battery voltage offset 1 0x48 fe -2mv used to adjust the battery voltage offset according to the following: voltage = (v sb (mv) + v off ) ? voltage gain temperature offset 1 0x49 8a 13.8 c the default value (zero adjustment) for the offset is 12.8 c or 0x80. toff new = toff current + (temp actual - temp reported ) ? 10 maximum temperature and ? t step 0x4a 5f maximum temperature = 61.0 c ? t step = 4.6 c maximum charge temperature is 69- (mt ? 1.6) c (mt = upper nibble). the ? t step is (dt ? 2 + 16)/10 c (dt = lower nibble). charge efficiency 0x4b ff maintenance compensation = 100% fast compensa - tion = 100% sets the fast-charge (high) and maintenance charge (low) efficiencies. the upper nibbles sets the low effi - ciency and the lower nibble adjusts the high effi - ciency according to the equation: nibble = (efficiency% ? 256 - 196)/4 full-charge percentage 0x4c 9c 100% this packed field is the two?s complement of the de - sired value in rm when the bq2040 determines a full-charge termination. if rm is below this value, rm is set to this value. if rm is above this value, then rm is not adjusted. note: 1. can be adjusted to calibrate the battery pack. table 10. example register contents (continued) 25 bq2040 description eeprom address eeprom hex contents example values notes low byte high byte low byte high byte digital filter 0x4d 96 0.30mv used to set the digital magnitude filter as described in table 2. current integra - tion gain 1 0x4e 40 0 3.2/0.05 represents the following: 3.2/sense resistor in ohms. it is used by the bq2040 to scale the measured voltage values on the sr pin in ma and mah. this register also compensates for variations in the reported sense resistor value. self-discharge rate 0x4f 2d 0.25% this packed field is the two?s complement of (52.73/x) where x is the desired self-discharge rate per day (%) at room temperature. voltage gain 1 0x56 0x57 17 07 7.09 voltage gain is packed as two units. for example, (r4 + r5)/r4 = 7.09 would be stored as: whole number stored in 0x57 as 7 and the decimal component stored in 0x56 as 256 x 0.09 = 23(= 17h). reserved 0x58 0x59 00 00 0 should be programmed to 0. edvf charging current 0x5a 0x5b 64 00 100ma contains the desired charge current below edvf. end of discharge voltage 1 0x5c 0x5d 20 d1 12000mv the value programmed is the two?s complement of the threshold voltage in mv. end-of-discharge voltage final 0x5e 0x5f 40 d4 11200mv the value programmed is the two?s complement of the threshold voltage in mv. full charge capacity 0x60 0x61 d0 07 2000ma this value sets the initial estimated pack capacity. ? t step 0x62 0f 20s the ? t step for ? t/ ? t termination equals 320 - (byte value ? 20). hold-off time 0x63 00 320s hold-off the hold-off time is 320 - (byte value ? 20). eeprom check 2 0x64 b5 181 must be equal to 0xb5. reserved 0x65 0x7f na not currently used by the bq2040. note: 1. can be adjusted to calibrate the battery pack. table 10. example register contents (continued) 26 bq2040 string description address 0x x0 0x x1 0x x2 0x x3 0x x4 0x x5 0x x6 0x x7 0x x8 0x x9 0x xa 0x xb manufacturer name 0x20- 0x2b 09 42 b 45 e 4e n 43 c 48 h 4d m 41 a 52 r 51 q -- device name 0x30- 0x37 06 42 b 51 q 32 2 30 0 34 4 30 0 - device chemistry 0x40- 0x45 04 6c l 69 i 4f o 4e n - manufacturer data 0x50- 0x55 05 42 b 51 q 32 2 30 0 32 2 table 11. example register contents (string data) 27 bq2040 absolute maximum ratings symbol parameter minimum maximum unit notes v cc relative to v ss -0.3 +7.0 v all other pins relative to v ss -0.3 +7.0 v ref relative to v ss -0.3 +8.5 v current limited by r11 (see figure 1) v sr relative to v ss -0.3 +7.0 v minimum 100 ? series resistor should be used to protect sr in case of a shorted battery. t opr operating tempera - ture 0 +70 c commercial note: permanent device damage may occur if absolute maximum ratings are exceeded. functional opera - tion should be limited to the recommended dc operating conditions detailed in this data sheet. expo - sure to conditions beyond the operational limits for extended periods of time may affect device reliability. dc voltage thresholds (t a =t opr ; v = 3.0 to 5.5v) symbol parameter minimum typical maximum unit notes e vsb battery voltage error relative to sb -50mv - 50mv v see note note: the accuracy of the voltage measurement may be improved by adjusting the battery voltage offset and gain, stored in external eeprom. for best operation, v cc should be 1.5v greater than v sb . 28 bq2040 recommended dc operating conditions (t a = t opr ) symbol parameter minimum typical maximum unit notes v cc supply voltage 3.0 4.25 6.5 v v cc excursion from < 2.0v to 3.0v initializes the unit. v ref reference at 25c 5.7 6.0 6.3 v i ref = 5 a reference at -40c to +85c 4.5 - 7.5 v i ref = 5 a r ref reference input impedance 2.0 5.0 - m ? v ref = 3v i cc normal operation - 90 135 av cc = 3.0v - 120 180 av cc = 4.25v - 170 250 av cc = 5.5v v sb battery input 0 - v cc v r sbmax sb input impedance 10 - - m ? 0 < v sb < v cc i disp disp input leakage - - 5 av disp = v ss i lvout v out output leakage -0.2 - 0.2 a eeprom off v sr sense resistor input -0.3 - 2.0 v v sr 29 bq2040 symbol parameter min max units notes f smb smbus operating frequency 10 100 khz t buf bus free time between stop and start condition 4.7 s t hd:sta hold time after (repeated) start condition 4.0 s t su:sta repeated start condition setup time 4.7 s t su:sto stop condition setup time 4.0 s t hd:dat data hold time 300 ns t su:dat data setup time 250 ns t low clock low period 4.7 s t high clock high period 4.0 s t f clock/data fall time 300 ns t r clock/data rise time 1000 ns t low:sext cumulative clock low extend time (slave) 25 ms t timeout 25 35 ms ac specifications td294501.eps t su:sta smbc smbd t su:sto t buf t hd:sta t low t su:dat t r t f t high t hd:dat bus timing data 30 bq2040 16-pin soic narrow (sn) 16-pin sn ( soic narrow ) dimension minimum maximum a 0.060 0.070 a1 0.004 0.010 b 0.013 0.020 c 0.007 0.010 d 0.385 0.400 e 0.150 0.160 e 0.045 0.055 h 0.225 0.245 l 0.015 0.035 all dimensions are in inches. a a1 .004 c b e d e h l 31 bq2040 ordering information bq2040 package option: sn = 16-pin narrow soic device: bq2040 gas gauge ic with smbus interface temperature range: blank = commercial (0 to 70c) changeno. page no. description of change 3 3 updated recommended application schematic. 3 9 changed overcurrent fault conditon for chargingcurrent < 1024ma. 3 10 4hz operation of led clarification. 3 11 added descriptions for bits 7 and 13 of batterymode. 3 14 atratetimetoempty and atratetimetofull invalid data indication correction. 3 15, 16 runtimetoempty, averagetimetoempty and averagetimetofull invalid data indication corrections. 3 23 changed typical battery low % value for li-ion with edv1 = 3.0v/cell. 3 24 li-ion taper current is stored in 2?s complement. 324 changed typical ? t step and full-charge percentage for li-ion. 3 25 voltage gain is (r4 + r5)/r4. 3 25 changed typical edv1 and edvf values for li-ion. 4 6 added v sb should not exceed 2.4v 4 8 the self discharge rate approximately doubles or halves 4 11 changed cycle count increase from 30 to 32 for condition request. 4 14 changed atrateok() indication from edv1 to edvf 4 25 changed self-discharge programming from 52.75/x to 52.73/x. 4 25 changed recommended edvf charging current from 0ma to 100ma notes: changes 1 and 2 refer to the 1998 data book change 3 = june1998 d changes from jan. 1998 c. change 4 = june 1999 e changes from june 1998 d. data sheet revision history 32 bq2040 copyright ? 1999, unitrode corporation all rights reserved. no part of this data sheet may be reproduced in any form or means, without express permission from unitrode. unitrode reserves the right to make changes in its prod - ucts without notice. unitrode assumes no responsibility for use of any products or circuitry described within. no license for use of intel - lectual property (patents, copyrights, or other rights) owned by unitrode or other parties is granted or implied. unitrode does not authorize the use of its components in life-support systems where failure or malfunction may cause injury to the user. if unitrode components are used in life-support systems, the user assumes all responsibili - ties and indemnifies unitrode from all liability or damages. benchmarq is a registered trademark of unitrode corporation printed in u.s.a. 17919 waterview parkway dallas, texas 75252 fax: (972) 437-9198 tel: (972) 437-9195 www.benchmarq.com or www.unitrode.com |
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