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1 of 22 general description the ds2786 estimates available capacity for rechargeable li-ion and li-ion polymer batteries based on the cell voltage in the open-circuit state following a relaxation period. the open-circuit voltage (ocv) is used to determine relative cell capacity based on a lookup table stored in the ic. this capability makes accurate capacity information available immediately after a battery pack is inserted. during periods of moderate to high rate discharging, which preclude ocv measurements, the ds2786 uses coulomb counting as a secondary means of estimating relative capacity. remaining capacity is reported in percent, along with cell voltage, current and temperature information. cell characteristics and application parameters used in the calculations are stored in on-chip eeprom. the ds2786 is intended for use on the host side of portable devices, though it can also be mounted within a battery pack. measurement and estimated capacity data are accessed through an i 2 c interface. temperature data is available from an on-die sensor. resistance measurements of a pack identification resistor and pack thermistor are supported by ratiometric measurements on two auxiliary inputs. applications 3g multimedia wireless handsets digital still cameras digital audio (mp3) players typical operating circuit features ? relative capacity calculated from combination coulomb counter and open- circuit cell voltage (ocv) battery model ? accurate warning of low battery conditions even on first cycle (no learn cycle needed) ? 12-bit battery voltage measurement: 10mv accuracy 1.22mv lsb, 0v to 4.5v input range ? 11-bit bidirectional current measurement: 25 ? v lsb, 51.2mv dynamic range 1.67ma lsb, 3.4a (r sns = 15m ? ) ? current accumulation measurement resolution: 204.8mvh range 13.65ah (r sns = 15m ? ) ? internal temperature measurement: 0.125c lsb, 3c accuracy ? two 11-bit aux input voltage measurements: 8 lsb accuracy, ratiometric inputs eliminate supply accuracy issues ? v out pin drives resistive dividers, reduces current consumption ? 2-wire interface ? low power consumption: active current: 50 ? a typ, 80 ? a max sleep current: 1 ? a typ, 3 ? a max ordering information part temp range pin-package DS2786G+ -20oc to +70oc 10 tdfn-ep* DS2786G+t&r -20oc to +70oc 10 tdfn-ep* +denotes a lead(pb)-free/rohs-compliant package. t&r = tape and reel. *ep = exposed pad. pin configuration 3mm x 3mm tdfn-10 top view ds2786 stand-alone ocv-based fuel gauge www.maxim-ic.com commands, registers, and modes are capitalized for clarity. 1 9 - 4 6 3 7 ; 5 / 0 9 downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 2 of 22 absolute maximum ratings voltage range on all pins except v prog relative to v ss -0.3v to +6v voltage range on v prog relative to v ss -0.3v to +18v operating temperature range -40c to +85c storage temperature range -55c to +125c soldering temperature refer to the ipc/jedecj-std-020 specification. this is a stress rating only and functional operation of the device at t hese or any other conditions above those indicated in t he operation sections of this specif ication is not implied. exposure to absolute ma ximum rating conditions for extended periods of time may affect reliability. recommended dc ope rating conditions (2.5v ? v dd ? 4.5v, t a = -20 ? c to +70 ? c.) parameter symbol conditions min typ max units supply voltage v dd (note 1) +2.5 +4.5 v data i/o pins scl, sda (note 1) -0.3 +4.5 v programming pin v prog (note 1) -0.3 +15.5 v vin, ain0, ain1 pin v in , ain0, ain1 (note 1) -0.3 v dd + 0.3 v dc electrical characteristics (2.5v ? v dd ? 4.5v, t a = -20 ? c to +70 ? c, unless otherwise noted.) parameter symbol conditions min typ max units active current i active 50 75 ? a v dd = 2.0v, scl, sda = v ss 0.3 1.0 sleep-mode current i sleep scl, sda = v ss 1 3 ? a current measurement resolution i lsb ds2786 25 ? v current measurement full-scale magnitude i fs (note 1) 51.2 mv current measurement offset error i oerr ds2786 (note 2) -50 +50 ? v current measurement gain error i gerr -1.5 +1.5 % of reading v dd = 3.6v at +25c -1 +1 t a = 0 ? c to +70 ? c -2 +2 timebase accuracy t err t a = -20 ? c to +70 ? c -3 +3 % v dd = v in = 3.6v, t a = 0 ? c to +50 ? c -10 +10 voltage error v gerr t a = -20 ? c to +70 ? c -20 +20 mv input resistance vin, ain0, ain1 r in 15 m ? ain0, ain1 error -8 +8 lsb v out output drive i o = 1ma v dd - 0.5 v downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 3 of 22 parameter symbol conditions min typ max units v out precharge time t pre 13.2 13.7 14.2 ms temperature error t err -3 +3 c input logic high: scl, sda v ih (note 1) 1.4 v input logic low: scl, sda v il (note 1) 0.6 v output logic low: sda v ol i ol = 4ma (note 1) 0.4 v pulldown current: scl, sda i pd v dd = 4.2v, v pin = 0.4v 0.2 1.0 ? a v prog pulldown r vprog 20 k ? input capacitance: scl, sda c bus 50 pf bus low timeout t sleep (note 3) 1.5 2.2 s eeprom programming voltage v prog 14 15 v eeprom programming current i prog 2 ma eeprom programming time t prog 3.1 14 ms eeprom copy endurance 100 writes electrical characteristics: 2-wire interface (2.5v ? v dd ? 4.5v, t a = -20 ? c to +70 ? c.) parameter symbol conditions min typ max units scl clock frequency f scl (note 4) 0 400 khz bus free time between a stop and start condition t buf 1.3 s hold time (repeated) start condition t hd:sta (note 5) 0.6 s low period of scl clock t low 1.3 s high period of scl clock t high 0.6 s setup time for a repeated start condition t su:sta 0.6 s data hold time t hd:dat (notes 6, 7) 0 0.9 s data setup time t su:dat (note 6) 100 ns rise time of both sda and scl signals t r 20 + 0.1c b 300 ns fall time of both sda and scl signals t f 20 + 0.1c b 300 ns setup time for stop condition t su:sto 0.6 s downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 4 of 22 parameter symbol conditions min typ max units spike pulse widths suppressed by input filter t sp (note 8) 0 50 ns capacitive load for each bus line c b (note 9) 400 pf scl, sda input capacitance c bin 60 pf note 1: all voltages are referenced to v ss . note 2: offset specified after auto-calibration cycle and current offset bias register = 00h. note 3: the ds2786 enters the sleep mode 1.5s to 2.2s after (scl < v il ) and (sda < v il ). note 4: timing must be fast enough to prevent the ds2786 from entering sleep mode due to bus low for period > t sleep . note 5: f scl must meet the minimum clock low time plus the rise/fall times. note 6: the maximum t hd:dat has only to be met if the device does not stretch the low period (t low ) of the scl signal. note 7: this device internally provides a hold time of at least 100ns for the sda signal (referred to the v ihmin of the scl signal) to bridge the undefined region of the falling edge of scl. note 8: filters on sda and scl suppress noise spikes at the input buffers and delay the sampling instant. note 9: c b total capacitance of one bus line in pf. figure 1. 2-wire bus timing diagram downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 5 of 22 pin description pin name function 1 ain1 aux voltage input number 1 2 ain0 aux voltage input number 0 3 scl serial clock input. input only 2-wire clock line. connect this pin to the clock signal of the 2-wire interface. this pin has a 0.2a typical pulldown to sense disconnection. 4 sda serial data input/output. open drain 2-wire data line. connect this pin to the clock signal of the 2-wire interface. this pin has a 0.2a typical pulldown to sense disconnection. 5 sns current-sense input. connect to the handset side of the sense resistor. 6 v ss device ground. connect to the battery side of the sense resistor. 7 v prog eeprom programming voltage input. connect to external supply for production programming. connect to v ss during normal operation. 8 v out voltage out. supply for aux input voltage measurement dividers. connect to high side of resistor divider circuits. 9 v in battery voltage input. the voltage of the cell pack is measured through this pin. 10 v dd power-supply input. 2.5v to 4.5v input range. connect to system power through a decoupling network. pad pad exposed pad. connect to v ss . figure 2. block diagram vin ain0 downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 6 of 22 description the ds2786 provides curre nt-flow, voltage, and temperature measur ement data to support battery-capacity monitoring in cost-sensitive applications. current is meas ured bidirectionally over a dynamic range of 51.2mv with a resolution of 25v. assuming a 15m ? sense resistor, the current sense range is 3.4a, with a 1 lsb resolution of 1.667ma. current measurements are performed at regula r intervals and accumulated with each measurement to support coulomb counting during periods of host power consumption. each current m easurement is reported with sign and magnitude in the two-byte current register. batte ry voltage measurements are reported in the two-byte voltage register with 12-bit (1.22mv) resolution, and aux iliary voltage measurements are reported in the two-byte aux volt registers with 11-bit resolution. additionally, t he temperature register reports temperature with 0.125oc resolution and 3oc accuracy from the on-chip sensor . the on-chip temperature measurement is optional and replaces the auxiliary voltage channel ain1. the ds2786 provides accurate relative capacity measurement s during periods of host system inactivity by looking at cell open circuit voltage. cell capacity is calculated using an ocv voltage profile and a 1-byte scale factor to weight accumulated current during th e coulomb-counting periods. the ocv voltage profile and scale factor are stored in eeprom memory. the eeprom memory is constructed with a sr am shadow so that the ocv voltage profile and scale factor can be overwritten by the host to accommodate a variety of cell types and capacities from multiple cell vendors. the i 2 c interface also allows read/write acce ss to the status, configuration, and measurement registers. figure 3. application example downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 7 of 22 power modes the ds2786 operates in one of two power modes: active and sleep. while in active mode, the ds2786 operates as a high-precision battery monitor with temperature, voltage, auxiliary inputs, curr ent, and accumulated current measurements acquired continuously a nd the resulting values updated in t he measurement registers. in sleep mode, the ds2786 operates in a low-power mode with no measurement activity. read and write access is allowed to all registers in either mode. the ds2786 operating mode transitions from sleep to active when: ( scl > v ih ) or ( sda > v ih ) the ds2786 operating mode transitions from active to sleep when: smod = 1 and [ ( scl < v il ) and ( sda < v il ) ] for t sleep caution: if smod = 1, a pullup resistor is required on scl and sda in order to ensure that the ds2786 transitions from sleep to active mode when the battery is charged. if the bus is not pulled up, the ds2786 remains in sleep and cannot accumulate the charge current. this c aution statement applies particularly to a battery that is charged on a stand-alone charger. parameter measurement the ds2786 uses a sigma delta a/d converter to make measurements. the measurement sequence shown in figure 4 repeats continuously while t he ds2786 is in active mode. the v out pin is activated t pre before the ain0 and ain1 conversion to allow for the v out output voltage to settle. the ds2 786 can be configured to measure temperature using its on-chip sensor instead of the ain1 input. when the in ternal temperature measurement uses the ain1 conversion timeslot, v out is not activated. a full sequence of voltage measurements nominally takes 1760ms to complete. figure 4. measurement sequence downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 8 of 22 voltage measurement battery voltage is measured at the v in input with respect to v ss over a range of 0v to 4.5v and with a resolution of 1.22mv. the result is updated every 880ms and placed in the voltage register in twos complement form. voltages above the maximum register value are reported as 7fffh. figure 5. voltage register format msbaddress 0ch lsbaddress 0dh s 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 x x x msb lsb msb lsb s: sign bit(s), x: reserved units: 1.22mv the input impedance of v in is sufficiently large (>15m ? ) to be connected to a high-impedance voltage divider in order to support multiple-cell applications. the pack voltage should be divided by the number of series cells to present a single-cell average voltage to the v in input. every 1024th conversion, the adc measures its input offset to facilitate offset correction to improve voltage accuracy. offset correction occurs approximately every 15 minutes. the resulting correction factor is applied to the subsequent 1023 measurements. during the offset corr ection conversion, the adc does not measure the v in signal. the voltage measurement just prior to the offset c onversion is displayed in the voltage register. the ocv algorithm automatically adjusts for the e ffects of the offset correction cycle. auxilary input measurements the ds2786 has two auxiliary voltage m easurement inputs, ain0 and ain1. bo th are measured with respect to v ss . these inputs are designed for measuring resistor ratios, particularly useful for measuring thermistor or pack identification resistors. prior to the beginning of a measurement cycle on ain0 or ain1, the v out pin outputs a reference voltage in order to drive a resistive divider formed by a known resistor value, and the unknown resistance to be measured. this technique deliver s good accuracy at a reasonable cost, as it removes reference tolerance from the error calculations. measurem ents alternate between each input. each auxiliary measurement is therefore updated every 1760ms and placed in the corresponding ain0 or ain1 register in twos complement form. figure 6. auxiliary input registers format ain0 msbaddress 08h lsbaddress 09h s 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 x x x x msb lsb msb lsb s: sign bit, x: reserved units: v out 1/2047 ain1 msbaddress 0ah lsbaddress 0bh s 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 x x x x msb lsb msb lsb s: sign bit, x: reserved units: v out 1/2047 downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 9 of 22 temperature measurement the ds2786 uses an integrated temperature sensor to meas ure battery temperature with a resolution of 0.125c. temperature measurements are updated every 1760ms and placed in the temperature register in twos complement form. the format of the temperature regi ster is shown in figure 7. the itemp bit in the status/configuration register must be set to enable the internal temperature measur ement instead of the ain1 measurement. figure 7. temperature register format msbaddress 0ah lsbaddress 0bh s 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 x x x x x msb lsb msb lsb s: sign bit(s), x: reserved units: 0.125 ? c current measurement in the active mode of operation, the ds2786 continually meas ures the current flow into and out of the battery by measuring the voltage drop across a low-value current-sense resistor, r sns , connected between the sns and v ss pins. the voltage sense range between sns and v ss is 51.2mv. note that positive current values occur when v sns is less than v ss , and negative current values occur when v sns is greater than v ss . peak signal amplitudes up to 102mv are allowed at the input as long as the continuous or average sign al level does not exceed 51.2mv over the conversion cycle period. the ad c samples the input differentially and updates the current register every 880ms at the completion of each conversion cycle. figur e 8 describes the current measurement register format and resolution for each option. charge currents above the maximum register value are reported at the maximum value (7fffh = +51.2mv). discharge currents below the minimum register value are reported at the minimum value (8000h = -51.2mv). every 1024th conversion, the adc measures its input offset to facilitate offs et correction to improve current accuracy. offset correction occurs approximately every 15 minutes. the resulting correction factor is applied to the subsequent 1023 measurements. during the offset correction conversion, the adc does not make a measurement. the current measurement just prior to the offset conversion is displayed in the current register. figure 8. current register formats msbaddress 0eh lsbaddress 0fh s 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 x x x x msb lsb msb lsb s: sign bit units: 25 ? v/r sns downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 10 of 22 table 1. current range and resolution for various r sns values current resolution (1 lsb) r sns |v ss - v sns | 20m ? 15m ? 10m ? 5m ? 25 ? v 1.25ma 1.667ma 2.5ma 5ma current input range r sns v ss - v sns 20m ? 15m ? 10m ? 5m ? 51.2mv 2.56a 3. 41a 5.12a 10.24a current offset bias the current offset bias register (cobr) allows a programmable offset value to be added to raw current measurements. the result of the raw current measurement plus the cobr value is displayed as the current measurement result in the current register, and is used for current accumulation and detection of an ocv condition. the cobr value can be used to correct for a stat ic offset error, or can be used to intentionally skew the current results and therefore the current accumulation. read and write access is allowed to cobr. whenever the cobr is written, the new value is applied to all subsequent current measurements. cobr can be programmed in 25 ? v steps to any value between +3.175mv and -3.2mv. the cobr value is stored as a twos comp lement value in nonvolatile (nv) memory. the cobr factory default value is 00h. figure 9. current offset bias register format address 60h s 2 6 2 5 2 4 2 3 2 2 2 1 2 0 m s b l s b s: sign bit units: 25 ? v/r sns current accumulation an internal accumulated current register (iacr) serves as an up/down counter holding a running count of charge since the last ocv condition. curren t measurement results, plus a programmable bias value are internally summed, or accumulated, at the completion of each current measurement conver sion period. the iacr has a range of 204.8mvh. the iacr uses the initial or learne d cell capacity registers to increment or decrement the relative capacity register as current flows into or out of the battery. in this way, the fuel gauge is accurate even when an ocv condition does not occur for an extended time period. table 2. accumulated current range for various r sns values iacr range r sns v ss - v sns 20m ? 15m ? 10m ? 5m ? 204.8mvh 10.24ah 13.65ah 20.48ah 40.96ah downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 11 of 22 cell capacity estimation the ds2786 uses a hybrid ocv measurement and coulomb c ounting algorithm to estimate remaining cell capacity. during periods of charging or dischargin g of the cell, the ds2786 counts charge flow into and out of the cell. when the application becomes inactive, the ds2786 waits for the cell voltage to relax and then adjusts the coulomb count based on an open-circuit voltage cell model stored in device eeprom. the resulti ng calculation is reported to the system as a percentage value between 0% and 100%. as the cell ages, a learn feature adjusts for changes in capacity. the relative capacity register reports remaining cell charge as a percentage of full. relative capacity is reported with a resolution of 0.5% and is limited to a value betw een 0% and 100%. the relative capacity register is updated each time the ic performs a current measurement or open-circuit cell voltage measurement. figure 10. relative cap acity register format address 02h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 m s b l s b units: 0.5% prior to the first learn operation, the relative capacity value is calculated by adding the iacr multiplied by the initial capacity scaling factor (7ah) to the last ocv relative capacity (16h). after the first learn operation, the relative capacity value is calculated by adding the iacr multiplied by the learned capacity scaling factor (17h) to the last ocv relative capacity (16h). each capacity scaling factor register has a re solution of 78.125%/vh and a maximum range of 0 to 19921.875%/vh. during assembly, the initia l capacity register should be progra mmed to the capacity of the cell. for example, an application using a 1ah cell and 0.015 ? sense resistor would set the initial capacity register to a value of (100% (1ah 0.015 ? )) 78.125%/vh = 55h. the learned capaci ty scaling factor register is controlled by the ds2786. the power up value is 00h, an d the register is updated with the calculated new cell capacity value after every learn operation. figure 11. initial capacity sca ling factor register format address 7ah 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 m s b l s b units: 78.125%/vh figure 12. learned capacity sca ling factor register format address 17h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 m s b l s b units: 78.125%/vh downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 12 of 22 ocv detection and current blanking the blanking/ocv threshold register sets the current measurement level at which the ds2786 switches between coulomb counting and open-circuit voltage measurement. when the magnitude of the measured current (after cobr is applied) is less than the value defined by the blanking/ocv threshold register, the measurement is not summed into the iacr. instead, the iacr is mainta ined at its present value and the ds2786 begins dv/dt measurement evaluation to detect an ocv voltage condi tion. a threshold value that is below the minimum operational current, but above the maximum idle current of the application should be selected. the blanking/ocv threshold register has a resolution of 25 ? v/r sns , and a range from 0mv/r sns to 6.375mv/r sns . the factory default value is 06h figure 13. blanking/ocv thr eshold register format address 7bh 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 m s b l s b units: 25 ? v/r sns while the measured current is below the blanking/ocv threshold level, th e ds2786 actively searches for a relaxed cell by calculating the change in cell voltage as re ported in the voltage register over 15 minute intervals (dv/dt). if the 15 minute dv/dt change of the voltage regi ster is less than the value stored in the ocv dv/dt threshold register, the ds2786 determines that the cell is now in a relaxed state and the relative capacity register is adjusted based on the ocv cell model st ored in parameter eeprom. this operation will occur repeatedly every 15 minutes until the ds2786 return s to coulomb-counting mode of operation. the ocv dv/dt threshold register has a resolution of 1.22mv/15min and a range from 0mv/15min to 18.3mv/15min. the factory default value is 3.66mv/15min. no te that the upper 4 bits of the ocv dv/dt threshold register are used to eeprom back bits from the status/configuration register. figure 14. ocv dv/dt thr eshold register format address 7ch smod ldis vodis itemp 2 3 2 2 2 1 2 0 m s b l s b units: 1.22mv/15min downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 13 of 22 ocv cell model the ocv cell model is a 9-point piece-wise linear appr oximation of open circuit cell voltage versus the remaining capacity of the cell. whenever an ocv update occurs, the relative capacity register is adjusted to a new value based on the ocv voltage reading and a linear approximat ion of the table values. figure 15 shows the factory- default cell model stored in eeprom. figure 15. default ocv cell model 3 3.2 3.4 3.6 3.8 4 4.2 0% 20% 40% 60% 80% 100% the ocv cell model can be modified by changing the c apacity and voltage breakpoint registers in eeprom. capacity 0 is fixed at 0% and cannot be changed. capacity 1 through capacity 7 are stored with 0.5% resolution at addresses 61h through 67h respectively. capacity values must be monotonic (capacity 1 > capacity 0, capacity 2 > capacity 1, etc.), but otherwise can be written to any value betw een 0.5% to 99.5%. capacity 8 is fixed at a value of 100% and cannot be changed. voltage breakpoints require two bytes per breakpoint, but are otherwise stored in a similar manner. voltage breakpoint 0: msb stored at address 68h, lsb stor ed at address 69h. other voltage breakpoints stored sequentially through address location 79h . each voltage breakpoint has a resolution of 1.22mv, and a range from 0.0v to 4.996v (ic operation limited to 4.5v). volt age breakpoint values must also be monotonic. figure 16. capacity 1 to ca pacity 7 registers format address 61hC67h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 m s b l s b units: 0.5% breakpoint 8 4.171v 100% breakpoint 6 4.042 85% breakpoint 5 4.005 80% breakpoint 7 4.087v 90.5% breakpoint 4 3.831v 52.5% breakpoint 3 3.752 25% breakpoint 2 3.673v 10% breakpoint 1 3.619v 5% breakpoint 0 3.186v 0% downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 14 of 22 figure 17. voltage break point register format msbeven addresses 68hC78h lsbodd address 69hC79h 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 x x x x msb lsb msb lsb x: reserved units: 1.22mv initial capacity estimation the ds2786 calculates relative capacity immediately upon power up. during initialization, the ds2786 makes a voltage measurement and uses the ocv cell model data to determine a starting point for the relative capacity register. this estimation occurs regardless of the load on the cell. any error induced from cell loading will be removed at the next ocv adjustment. the initial voltage me asurement used in determining the starting point is stored in the initial voltage register until the ic is power cycled. figure 18. initial voltage register format msbaddress 14h lsbaddress 15h s 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 x x x msb lsb msb lsb s: sign bit(s), x: reserved units: 1.22mv new capacity learning as the cell ages, the initial capacity scaling factor r egister value may no longer accurately reflect the true capacity of the cell causing error in relative capacity calculation while in coulomb-counting m ode of operation. the ds2786 has a learn feature that allows the ic to remain accurate as the cell changes. the ds2786 compares the percent relative capacity difference between the last two ocv updates to the change in the coulomb count to learn the new cell capacity. the last ocv register mainta ins the relative capacity percentage at the previous ocv adjustment point used for learning the new cell capacity. last ocv w ill be updated with a ne w value at each ocv adjustment. example: assuming a 15m ? sense resistor, the ds2786 adjusts the rela tive capacity of a 1000mah cell to 10% based on an ocv measurement during an idle period of the application. the cell is then charged by 500mah (to 60% expected) based on the internal coulomb count mult iplied by the learned capacity scaling factor value of 55h. the next ocv adjustment determines the relative capa city should actually be at 65%, not 60%. the ds2786 then adjusts the learned capacity scaling factor value upward to (65% - 10%) (500mah 0.015 ? ) = 5eh lowering the expected cell capacity by approximately 10%. downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 15 of 22 figure 19. last ocv register format address 16h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 m s b l s b units: 0.5% the learn delta percent threshold allows the application to select how large of a cell capacity change is required before the new cell capacity value is learned. the difference between the present ocv measurement and the last ocv measurement must be greater than the learn delta percent threshold value for a learn to occur. this prevents ic measurement resolution fr om adding error to the learned cell capacity value. it is recommended this register be set to a value of at least 50%. figure 20. learn delta percent threshold address 7eh 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 m s b l s b units: 0.5% memory map the ds2786 has memory space with registers for instrum entation, status, and control. when the msb of a two- byte register is read, both the msb and lsb are latched and held for the duration of the read data command to prevent updates during the read and ensure synchronization between the two register bytes. for consistent results, always read the msb and the lsb of a two-byte regi ster during the same read data command sequence. memory locations 60h through 7fh ar e eeprom storage locations. eeprom memory is shadowed by ram to eliminate programming delays between writes and to allow th e data to be verified by the host system before being copied to eeprom. the read data and write data pr otocols to/from eeprom memo ry addresses access the shadow ram. setting the rcall bit in the command register (feh) initiate data transf er from the eeprom to the shadow ram. setting the copy bit in the command regi ster initiates data transfer from the shadow ram to the eeprom. an external voltage supply must be provided on the vprog pin prior to writing the copy bit. the ds2786 requires the copy bit be reset to 0 within the t prog time window to properly progr am eeprom. resetting copy too soon may prevent a proper write of the cells. resetting copy too late may degrade eeprom copy endurance. the ds2786 uses shadow ram data for fuel gauge calcul ations. fuel gauge information can be changed in the application by writing the shadow ram locations. afterwar ds the socv bit should be written to reset the fuel gauge. note that any reset of the i.c. will caus e the shadow ram data to be restored from eeprom. figure 21. eeprom acces s via shadow ram serial interface write read shadow ram eeprom copy recall downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 16 of 22 table 3. memory map address (hex) description read/write 00h reserved 01h status/config register r/w 02h relative capacity r 03h to 07h reserved 08h auxiliary input 0 msb r 09h auxiliary input 0 lsb r 0ah auxiliary input 1 / temperature msb r 0bh auxiliary input 1 / temperature lsb r 0ch voltage register msb r 0dh voltage register lsb r 0eh current register msb r 0fh current register lsb r 10h to 13h reserved 14h initial voltage msb r 15h initial voltage lsb r 16h last ocv relative capacity r 17h learned capacity scaling factor r 18h to 5fh reserved 60h to 7fh parameter eeprom r/w 80h to fdh reserved feh command r/w ffh reserved table 4. parameter eeprom memory block address description factory value address description factory value 60h current offset bias register 00h 70h voltage breakpoint 4 msb c4h 61h capacity 1 0ah 71h voltage breakpoint 4 lsb 20h 62h capacity 2 14h 72h voltage breakpoint 5 msb cdh 63h capacity 3 32h 73h voltage breakpoint 5 lsb 10h 64h capacity 4 69h 74h voltage breakpoint 6 msb ceh 65h capacity 5 a0h 75h voltage breakpoint 6 lsb f0h 66h capacity 6 aah 76h voltage breakpoint 7 msb d1h 67h capacity 7 b5h 77h voltage breakpoint 7 lsb 40h 68h voltage breakpoint 0 msb a3h 78h voltage breakpoint 8 msb d5h 69h voltage breakpoint 0 lsb 20h 79h voltage breakpoint 8 lsb 90h 6ah voltage breakpoint 1 msb b9h 7ah initial capacity scaling factor 80h 6bh voltage breakpoint 1 lsb 50h 7bh blanking/ocv current threshold 06h 6ch voltage breakpoint 2 msb bch 7ch ocv dv/dt threshold 93h 6dh voltage breakpoint 2 lsb 10h 7dh i 2 c address configuration* 60h* 6eh voltage breakpoint 3 msb c0h 7eh learn threshold 78h 6fh voltage breakpoint 3 lsb 20h 7fh user eeprom 00h * the factory default 7-bit slave address is 0110110. the upper 3 bits are fixed at 011, the lower 4 bits can be changed by writi ng the i 2 c address configuration register as illustrated in figures 24 and 25 . downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 17 of 22 status/config register the status/config register is read/write with individual bits designated as read only. bit values indicate status as well as program or select device func tionality. bits 3 though 6 are eeprom ba cked at memory location 7ch. note that their bit positions differ between these locations. figure 22. status/conf ig register format address 01h bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 x porf smod ldis vodis itemp ain1 ain0 bit 7: x reserved. bit 6: porf the power-on-reset flag is set to indicate initia l power-up. porf is not cleared internally. the user must write this flag value to a 0 in order to use it to indicate subsequent power-up events. por event will cause a reset of the fuel gauge. porf is read/write-to-zero. bit 5: smod sleep mode enable. a value of 1 allows the ds2786 to enter sleep mode when scl and sda are low for t sleep . a value of 0 disables the transition to sleep mode. this bit is eeprom back ed by bit 7 of memory location 7ch. the factory programmed value is 1. caution: smod sleep feature must be disabled when a battery is charged on an external charger that does not connect to the sda or scl pins. smod sleep can be used if the charger pulls sda or scl high. the ds2786 remains in sleep on a charger that fails to properly driv e sda or scl and therefore does not adjust relative capacity when a battery is charged. bit 4: ldis learn disable. a value of 1 disables cell capacity learning by the ds2786. a value of 0 allows cell capacity learning to occur normally. this bit is eeprom backed by bit 6 of memory location 7ch. the factory programmed value is 0. bit 3 : vodis v out disable. a value of 1 disables the v out output. when set to 0 this output is driven t pre before the ain0 conversion begins, and disabl ed after the ain1 conversi on ends. this bit is eeprom backed by bit 5 of memory location 7ch. the factory-programmed value is 0. bit 2: itemp itemp. a value of 1 enables measurement of temp erature using the internal sensor during the ain1 conversion timeslot. ain1 input is not selected and v out is not enabled during the ain1 timeslot. a value of 0 restores the measurement of ain1 and enables v out during the ain1 timeslot. this bit is eeprom backed by bit 4 of memory location 7ch. the factory-programmed value is 1. bit 1 : ain1 ain1 conversion valid. this read only bit indicates that the v out output was enabled, and a conversion has occurred on the ain1 pin. when using the vodis bit, before reading the ain1 registers, read the ain1 bit. only once the ain1 bit is se t, should the ain1 register be read. bit 0 : ain0 ain0 conversion valid. this read only bit indicates that the v out output was enabled, and a conversion has occurred on the ain0 pin. when using the vodis bit, before reading the ain0 registers, read the ain0 bit. only once the ain0 bit is se t, should the ain0 register be read. downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 18 of 22 command register the command register is read/write accessible. bit values indicate operations requested to be performed by the device. figure 23. command register format address feh bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 por 0 x x pocv socv rcall copy bit 7: por power-on reset. a value of 1 starts a power-on re set event. the bit is cleared on the next start or stop on the 2-wire bus, ex iting the reset state. bit 6: 0 bit always reads logic 0. bits 5 and 4: x reserved. bit 3: pocv present ocv calculation. when set to one the part is performing an ocv calculation based on the voltage stored in the voltage register, and the ocv lookup table values present in the scratch pad. writing the bit to 1 forces a calculation. this func tion should be used for test purposes only. forcing an ocv calculation will create capacity estimation error. the bit is cl eared when the hardware completes the calculation. bit 2: socv stored ocv calculation. this command may be used to reset the relative capacity calculation after updating ocv cell model data in the scratchpad. when set to one the part is performing an ocv calculation based on the voltage stored in the initial voltage register, and the ocv lookup table values present in the scratch pad. writing the bit to 1 forces a calculation. forcing an ocv ca lculation will create capacity estimation error. the bit is cleared when the hardware completes the calculation. bit 1: rcall the recall bit is set to recall the cont ents of eeprom into the scratch pad. bit 0: copy the copy bit is set to start a copy command of the scratch pad to eeprom. a programming voltage must be present on the vprog pin prior for the copy to be successful. the copy bit must be cleared by software within the t prog time window. user eeprom location 7fh provides one byte avail able for storage of user-defined information. this byte does not affect operation of the fuel gauge. factory default is 00h. 2-wire bus system the 2-wire bus system supports oper ation as a slave only device in a single or multislave, and single- or multimaster system. the 2-wire interface consists of a se rial data line (sda) and serial clock line (scl). sda and scl provide bidirectional communicati on between the ds2786 slave device and a master device at speeds up to 400khz. the ds2786s sda pin operates bidirectionally, t hat is, when the ds2786 receives data, sda operates as an input, and when the ds2786 returns data, sda opera tes as an open-drain output, with the host system providing a resistive pullup. the ds2786 always operate s as a slave device, receiving and transmitting data under the control of a master device. the master initiates all transactions on the bus and generates the scl signal as well as the start and stop bits which begin and end each transaction. bit transfer one data bit is transferred during each scl clock cycle, with the cycle defined by scl transitioning low-to-high and then high-to-low. the sda logic level must remain stab le during the high period of the scl clock pulse. any change in sda when scl is high is interpreted as a start or stop control signal. downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 19 of 22 bus idle the bus is defined to be idle, or not busy, when no master device has control. both sda and scl remain high when the bus is idle. the stop condition is the prop er method to return the bus to the idle state. start and stop conditions the master initiates transactions with a start condition (s), by forcing a high-to-low transition on sda while scl is high. the master terminates a transaction with a stop condition (p), a low-to-high transition on sda while scl is high. a repeated start condition (sr) can be used in place of a stop then start sequence to terminate one transaction and begin another without returning the bus to the idle state. in multimaster systems, a repeated start allows the master to retain control of the bus. the start and stop conditions are the only bus activities in which the sda transitions when scl is high. acknowledge bits each byte of a data transfer is acknowledged with an a cknowledge bit (a) or a no acknowledge bit (n). both the master and the ds2786 slave generate acknowledge bits. to generate an acknowledge, the receiving device must pull sda low before the rising edge of the acknowledge-relate d clock pulse (ninth pulse) and keep it low until scl returns low. to generate a no acknowledge (also called na k), the receiver releases sda before the rising edge of the acknowledge-related clock pulse an d leaves sda high until scl returns low. monitoring the acknowledge bits allows for detection of unsuccessful data transfers. an un successful data transfer can occur if a receiving device is busy or if a system fault has occurred. in the event of an unsuccessful data transfer, the bus master should re- attempt communication. data order a byte of data consists of 8 bits order ed most significant bit (msb) first. the least significant bit (lsb) of each byte is followed by the acknowledge bit. ds2786 registers compos ed of multibyte values are ordered most significant byte (msb) first. the msb of multibyte register s is stored on even data memory addresses. slave address a bus master initiates communication with a slave dev ice by issuing a start condition followed by a slave address (saddr) and the read/write (r/ w ) bit. when the bus is idle, the ds2786 continuously monitors for a start condition followed by its slave a ddress. when the ds2786 re ceives a slave address that matches its slave address, it responds with an acknowled ge bit during the clock period following the r/ w bit. the factory default 7-bit slave address is 0110110. the upper 3 bits are fixed at 011, the lower 4 bits can be changed by writing the i 2 c address configuration regi ster at location 7dh. figure 24. i 2 c address configurat ion register format address 7dh bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 addr3 addr2 addr 1 addr0 x x x x bits 7 to 4: addr[3:0] user-adjustable bits of the ds2786s i 2 c address. factory default is 0110. bits 3 to 0: x reserved. figure 25. ds2786 i 2 c address byte format bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 0 1 1 addr3 addr2 addr1 addr0 r/ w downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 20 of 22 read/write bit the r/ w bit following the slave address determines the data direction of subsequent bytes in the transfer. r/ w = 0 selects a write transaction, with the following byte s being written by the ma ster to the slave. r/ w = 1 selects a read transaction, with the following bytes being read from the sl ave by the master. with the addr3Caddr0 bits at their default of 0110, writes occur using addre ss 0x6ch, while reads occur at 0x6dh. bus timing the ds2786 is compatible with any bus timing up to 400khz. no special configur ation is required to operate at any speed. 2-wire command protocols the command protocols involve several transaction formats. the simplest format consists of the master writing the start bit, slave address, r/ w bit, and then monitoring the acknowledge bi t for presence of the ds2786. more complex formats such as the write data, read data, and function command protocols write data, read data, and execute device specific operations. all bytes in each command format require the slave or host to return an acknowledge bit before continuing with the next byte. each function command definition outlines the required transaction format. the following key applies to the transaction formats. table 5. 2-wire protocol key key description key description s start bit sr repeated start saddr slave address (7-bit) w r/ w bit = 0 fcmd function command byte r r/ w bit = 1 maddr memory address byte p stop bit data data byte written by master data data byte returned by slave a acknowledge bitmaster a acknowledge bitslave n no acknowledgemaster n no acknowledgeslave basic transaction formats write: s saddr w a maddr a data0 a p a write transaction transfers one or more data bytes to the ds2786. the data transfer begins at the memory address supplied in the maddr byte. contro l of the sda signal is retained by t he master throughout the transaction, except for the acknowledge cycles. read: s saddr w a maddr a sr saddr r a data0 n p write portion read portion a read transaction transfers one or more bytes from the ds2786. read transactions are composed of two parts, a write portion followed by a read portion, and is therefore i nherently longer than a write transaction. the write portion communicates the starting point for the read operation. the read portion follows immediately, beginning with a repeated start, slave address with r/ w set to a 1. control of sda is assumed by the ds2786 beginning with the slave address acknowledge cycle. control of the sda signal is re tained by the ds2786 throughout the transaction, except for the acknowled ge cycles. the master indicates the end of a read transaction by responding to the last byte it requires with a no acknowledge. this signals the ds2786 that control of sda is to remain with the master following the acknowledge clock. downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 21 of 22 write data protocol the write data protocol is used to write to register and shadow ram data to the ds2786 starting at memory address maddr. data0 represents the da ta written to maddr, data1 represent s the data written to maddr + 1 and datan represents the last data byte, written to maddr + n. the master indicates the end of a write transaction by sending a stop or repeated start after receiving the last acknowledge bit. s saddr w a maddr a data0 a data1 a datan a p the msb of the data to be stored at address maddr can be written immediately after the maddr byte is acknowledged. because the address is automatically increm ented after the least significant bit (lsb) of each byte is received by the ds2786, the msb of the data at addr ess maddr + 1 is can be written immediately after the acknowledgement of the data at address maddr. if the bus master continues an auto-incremented write transaction beyond address 4fh, the ds2786 ignores the data. data is also ignored on writes to read-only addresses and reserved addresses, as well as a write that auto incremen ts to the function command register (address feh). incomplete bytes and bytes that are not acknowledged by the ds2786 are not written to memory. as noted in the memory section, writes to eeprom lo cations modify the shadow ram only. read data protocol the read data protocol is used to read register a nd shadow ram data from the ds2786 starting at memory address specified by maddr. data0 represents the data byte in memory location maddr, data1 represents the data from maddr + 1 and datan represents th e last byte read by the master. s saddr w a maddr a sr saddr r a data0 a data1 a datan n p data is returned beginning with the msb of the data in ma ddr. because the address is automatically incremented after the lsb of each byte is returned, the msb of t he data at address maddr + 1 is available to the host immediately after the acknowledgement of the data at add ress maddr. if the bus master continues to read beyond address ffh, the ds2786 outputs data values of ffh. addresses labeled reserved in the memory map (table 3) return undefined data. the bus master terminates the read transaction at any byte boundary by issuing a no acknowledge followed by a stop or repeated start. package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . package type package code document no. 10 tdfn-ep t1033+1 21-0137 downloaded from: http:///
ds2786 stand-alone ocv-based fuel gauge 22 of 22 maxim/dallas semiconductor cannot assume res ponsibility for use of any circuitry other than circuitry entirely embodied in a ma xim/dallas semiconductor product. no circuit patent licenses are implied. maxi m/dallas semiconductor reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2009 maxim integrated products the maxim logo is a registered trademark of maxim integrated products, inc. the dallas logo is a registered trademark of dallas semiconductor corporation. revision history revision date description pages changed in the recommended dc operating characteristics , changed the pio pin range to vprog pin range and changed the operating range to 15.5v. 2 corrected bit locations of vdis and lodis bits in eeprom (figure 14 and status/config register section). 12, 17 fixed grammatical error under ocv cell model section: required to require. 13 030708 fixed grammatical error describing copy bit under memory map section. 15 070808 in figure 23, changed bit 6 from x (reserved) to 0. 18 101708 changed operation to 4.5v maximum. 2, 3, 5, 8, 13 changed the v dd maximum operating range in the electrical characteristics table to 4.5v. 2, 3 051209 added v in pin is limited to v dd voltage text in the voltage measurement section. 8 downloaded from: http:///

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