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general description the ds2786b estimates available capacity for recharge-able li-ion (li+) and li+ polymer batteries based on the cell voltage in the open-circuit state following a relax- ation 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 dis- charging, which preclude ocv measurements, the ds2786b 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 ds2786b 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 mea-surements of a pack identification resistor and pack ther- mistor are supported by ratiometric measurements on two auxiliary inputs. the ds2786b comes in a 10-pin, lead-free, tdfn 3mm x 3mm package with an exposed pad (ep). applications 3g multimedia wireless handsetsdigital still cameras digital audio (mp3) players features ? relative capacity calculated from combinationcoulomb counter and open-circuit cell voltage (ocv) battery model ? accurate warning of low-battery conditionseven on first cycle (no learn cycle needed) ? 12-bit battery voltage measurement ?0mv accuracy1.22mv lsb, 0v to 4.5v input range ? 11-bit bidirectional current measurement 25? lsb, ?1.2mv dynamic range1.67ma lsb, ?.4a (r sns = 15m ) ? current accumulation measurement resolution ?04.8mvh range?3.65ah (r sns = 15m ) ? internal temperature measurement 0.125? lsb, ?? accuracy ? two 11-bit auxiliary input-voltage measurements ? lsb accuracy, ratiometric inputs eliminatesupply accuracy issues ? v out pin drives resistive dividers, reduces current consumption ? 2-wire interface ? low power consumption active current: 50? (typ), 80? (max)sleep current: 1? (typ), 3? (max) ds2786b stand-alone ocv-based fuel gauge ________________________________________________________________ maxim integrated products 1 ordering information r sns ain0 v out ain1 sda scl li+ protection circuit thermistor packid i 2 c interface system p v ss sns v in (eeprom programming test point not shown) ds2786b operating diagram 19-5223; rev 1; 4/10 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. t&r = tape and reel. part temp range pin-package ds2786bg+ -20c to +70c 10 tdfn-ep* ds2786bg+t&r -20c to +70c 10 tdfn-ep* downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 2 _______________________________________________________________________________________ absolute maximum ratingsdc electrical characteristics (2.5v v dd 4.5v, t a = -20 c to +70 c, unless otherwise noted.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. voltage on all pins except v prog relative to v ss ...-0.3v to +6v voltage on v prog relative to v ss ..........................-0.3v to +18v operating temperature range ...........................-40? to +85? storage temperature range .............................-55? to +125? lead temperature (soldering, 10s) .................................+300? soldering temperature (reflow) .......................................+260? 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 25 v current-measurement full-scale magnitude i fs (note 1) 51.2 mv current-measurement offset error i oerr (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 v in , ain0, ain1 r in 15 m ain0, ain1 error -8 +8 lsb v out output drive i o = 1ma v dd - 0.5 v v out precharge time t pre 13.2 13.7 14.2 ms temperature error t err -3 +3 c recommended dc operating procedure(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 v in , ain0, ain1 pin v in , ain0, ain1 (note 1) -0.3 v dd + 0.3 v downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge _______________________________________________________________________________________ 3 note 1: all voltages are referenced to v ss . note 2: offset specified after autocalibration cycle and current offset bias register = 00h. note 3: the ds2786b 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 ds2786b 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. parameter symbol conditions min typ max units 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 dc electrical characteristics (continued)(2.5v v dd 4.5v, t a = -20 c to +70 c, unless otherwise noted.) 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 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 downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 4 _______________________________________________________________________________________ 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 ?otal capacitance of one bus line in pf. electrical characteristics: 2-wire interface (continued)(2.5v v dd 4.5v, t a = -20 c to +70 c.) sda scl t f t low t hd:sta t hd:dat t su:sta t su:sto t su:dat t hd:sta t sp t r t buf t r t f ss r p s figure 1. 2-wire bus timing diagram downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge _______________________________________________________________________________________ 5 pin description pin name function 1 ain1 auxiliary voltage input number 1 2 ain0 auxiliary voltage input number 0 3 scl serial clock input. input only 2-wire clock line. connect this pin to the c lock 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 disconnect ion. 5 sns current-sense input. connect to the handset side of the sense r esistor. 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 p roduction programming. connect to v ss during normal operation. 8 v out voltage out. supply for auxiliary input voltage measureme nt 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 p in. 10 v dd power-supply input. 2.5v to 4.5v input range. connect to system power through a decoup ling network. ep exposed pad. connect to v ss . 1 34 10 87 v dd v out v prog ain1 ep scl sda 29 v in ain0 56 v ss sns tdfn (3mm x 3mm) top view ds2786b pin configuration downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 6 _______________________________________________________________________________________ 2-wire interface adc sdascl ic ground v dd v ss bias 1k 1k v in ain0 ain1 sns v out switch is on when ain0 or ain1 is being measured. voltage reference state machine eeprom v prog timebase temperature measurement figure 2. block diagram detailed description the ds2786b provides current-flow, voltage, and temperature-measurement data to support battery- capacity monitoring in cost-sensitive applications. current is measured bidirectionally over a dynamic range of ?1.2mv with a resolution of 25?. assuming a 15m sense resistor, the current-sense range is ?.4a, with a 1 least significant bit (lsb) resolution of1.667ma. current measurements are performed at reg- ular intervals and each measurement is accumulated internally to coulomb count host power consumption. each current measurement is reported with sign and magnitude in the 2-byte current register. battery-voltage measurements are reported in the 2-byte voltage register with 12-bit (1.22mv) resolution, and auxiliary voltage measurements are reported in the 2- byte aux volt registers with 11-bit resolution. additionally, the temperature register reports tempera- ture with 0.125? resolution and ?? accuracy from the on-chip sensor. the on-chip temperature measure- ment is optional and replaces auxiliary voltage channel ain1. figure 1 is the 2-wire bus timing diagram; figure 2 is the ds2786b block diagram. figure 3 is an appli- cation example. downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge _______________________________________________________________________________________ 7 the ds2786b provides accurate relative capacity mea-surements during periods of host system inactivity by looking at cell open-circuit voltage. cell capacity is cal- culated using an ocv voltage profile and a 1-byte scale factor to weight-accumulated current. the ocv voltage profile and scale factor are stored in eeprom memory. the eeprom memory is constructed with a sram shadow so that the ocv voltage profile and scale factor can be overwritten by the host to accom- modate a variety of cell types and capacities from mul- tiple-cell vendors. the i 2 c interface also allows read/write access to the status, configuration, andmeasurement registers. power modes the ds2786b operates in one of two power modes:active and sleep. while in active mode, the ds2786b operates as a high-precision battery monitor with temper- ature, voltage, auxiliary inputs, current, and accumulated current measurements acquired continuously and the resulting values updated in the measurement registers. insleep mode, the ds2786b operates in a low-power mode with no measurement activity. read-and-write access is allowed to all registers in either mode. the ds2786b operating mode transitions from sleep to active when: (scl > v ih ) or (sda > v ih ) the ds2786b operating mode transitions from active tosleep 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 ds2786b tran-sitions from sleep to active mode when the battery is charged. if the bus is not pulled up, the ds2786b remains in sleep and cannot accumulate the charge current. this caution statement applies particularly to a battery that is charged on a standalone charger. ain0 v in v out ain1 sda v ss scl (1) optional for 8kv/15kv esd sns v dd v prog pack- pack+ packid therm protection ic (li+/polymer) systemvss systemserial bus programmingtest point systemvdd battery system r sns 150 10nf 5.6v (1) 1k 1nf 1nf 1k 1k 2.5v (1) ds2786b figure 3. application example downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 8 _______________________________________________________________________________________ inactive inactive active (inactive for temperature measurement) v in pin measurement average over 440ms new register value new register value new register value 0.86msdelay 0.86msdelay 0.86msdelay 0.86msdelay t pre voltage register v out pin alternating ain0 or ain1/temperature measurement ain0 or ain1/ temperature register differential current measurement current register cycle of measurements repeats every 880ms. average over 220ms average over 220ms 440ms 220ms 220ms figure 4. measurement sequence parameter measurement the ds2786b uses a sigma-delta a/d converter tomake measurements. the measurement sequence shown in figure 4 repeats continuously while the ds2786b 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 ds2786b can be configured to measure temperature using its on-chipsensor instead of the ain1 input. when the internal tem- perature measurement uses the ain1 conversion time- slot, v out is not activated. a full sequence of voltage measurements nominally takes 1760ms to complete. downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge _______________________________________________________________________________________ 9 voltage measurement battery voltage is measured at the v in input with respect to v ss over a 0 to 4.999v range and with a resolution of 1.22mv. the result is updated every 880ms and placedin the voltage register in two?-complement form. voltages above the maximum register value are reported as 7fffh. figure 5 is the voltage register format. the input impedance of v in is sufficiently large (> 15m ) to be connected to a high-impedance volt- age-divider in order to support multiple-cell applica-tions. 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 inputoffset to facilitate offset correction to improve voltage accuracy. offset correction occurs approximately every 15min. the resulting correction factor is applied to the subsequent 1023 measurements. during the offset-cor- rection conversion, the adc does not measure the v in signal. the voltage measurement just prior to the offset conversion is displayed in the voltage register. theocv algorithm automatically adjusts for the effects of the offset-correction cycle. auxilary input measurements the ds2786b has two auxiliary voltage-measurementinputs, ain0 and ain1. both are measured with respect to v ss . these inputs are designed for measuring resis- tor ratios, particularly useful for measuring thermistor orpack identification resistors. prior to the beginning of a measurement cycle on ain0 or ain1, the v out pin out- puts a reference voltage in order to drive a resistivedivider formed by a known resistor value, and the unknown resistance to be measured. this technique delivers good accuracy at a reasonable cost, as it removes reference tolerance from the error calcula- tions. measurements alternate between each input. each auxiliary measurement is therefore updated every 1760ms and placed in the corresponding ain0 or ain1 register in two?-complement form. figure 6 shows the auxiliary input registers 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, x: reserved units: 1.22mv figure 5. voltage register 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 figure 6. auxiliary input registers format downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 10 ______________________________________________________________________________________ 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, x: reserved units: 0.125 c figure 7. temperature register format 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, x: reserved units: 25v/r sns figure 8. current register formats current resolution (1 lsb) r sns |v ss - v sns | 20m 15m 10m 5m 25v 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 table 1. current range and resolution for various r sns values temperature measurement the ds2786b uses an integrated temperature sensor tomeasure battery temperature with a resolution of 0.125?. temperature measurements are updated every 1760ms and placed in the temperature register in two?-complement form. the format of the temperature register is shown in figure 7. the itemp bit in the status/configuration register must be set to enable the internal temperature measurement instead of the ain1 measurement. current measurement in the active mode of operation, the ds2786b continu-ally measures the current flow into and out of the bat- tery 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 ?1.2mv. note that positive current val- ues 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 signal leveldoes not exceed ?1.2mv over the conversion-cycle period. the adc samples the input differentially and updates the current register every 880ms at the com- pletion of each conversion cycle. figure 8 describes the current measurement register format and resolu- tion for each option. charge currents above the maxi- mum register value are reported at the maximum value (7fffh = +51.2mv). discharge currents below the mini- mum register value are reported at the minimum value (8000h = -51.2mv). every 1024th conversion, the adc measures its input offset to facilitate offset correction to improve current accuracy. offset correction occurs approximately every 15min. the resulting correction factor is applied to the subsequent 1023 measurements. during the offset cor- rection conversion, the adc does not make a measure- ment. the current measurement just prior to the offset conversion is displayed in the current register. see table 1 for current range and resolution for various r sns values. downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge ______________________________________________________________________________________ 11 current offset bias the current offset bias register (cobr) allows a pro-grammable offset value to be added to raw current measurements. the result of the raw current measure- ment 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 con- dition. the cobr value can be used to correct for a sta- tic 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 sub- sequent current measurements. cobr can be pro- grammed in 25? steps to any value between +3.175mv and -3.2mv. the cobr value is stored as a two?-complement value in nonvolatile (nv) memory. the cobr factory default value is 00h. figure 9 shows the current offset bias register format. 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. current mea- surement results, plus a programmable bias value are internally summed, or accumulated, at the completion of each current measurement-conversion period. the iacr has a range of ?04.8mvh. the iacr uses the initial or learned 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. see table 2 for the accumulated current range for various r sns values. cell-capacity estimation the ds2786b uses a hybrid ocv measurement andcoulomb-counting algorithm to estimate remaining cell capacity. during periods of charging or discharging the cell, the ds2786b counts charge flow into and out of the cell. when the application becomes inactive, the ds2786b 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 resulting calculation is reported to the system as a per- centage 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 between 0% and 100%. the relative capacity register is updated each time the ic performs a current measurement or open-circuit cell-voltage measurement. see figure 10. address 60h s 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb s: sign bit units: 25v/r sns figure 9. current offset bias register format iacr range r sns v ss - v sns 20m 15m 10m 5m 204.8mvh 10.24ah 13.65ah 20.48ah 40.96ah table 2. accumulated current range forvarious r sns values address 02h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 0.5% figure 10. relative capacity register format downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 12 ______________________________________________________________________________________ prior to the first learn operation, the relative capacityvalue is calculated by adding the iacr multiplied by the initial capacity scaling factor (7ah) to the last ocv rela- tive capacity (16h). after the first learn operation, the rel- ative 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 resolution of 78.125%/vh and a maximum range of 0 to 19921.875%/vh. during assembly, the initial capacity register should be programmed 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 x 0.015 ))/ 78.125%/vh = 55h. the learned capacity scaling factorregister is controlled by the ds2786b. the power-up value is 00h, and the register is updated with the calcu- lated new cell capacity value after every learn operation. see figures 11 and 12. ocv detection when the magnitude of the measured current (aftercobr is applied) is less than the value defined by the ocv threshold register, the ds2786b begins dv/dt measurement evaluation to detect an ocv voltage condition. a threshold value that is below the minimum operational current, but above the maximum idle cur-rent of the application should be selected. the ocv threshold register has a resolution of 25?/r sns , and a range from 0mv/r sns to 6.375mv/r sns . the factory default value is 28h. see figure 13 for the ocv thresh-old register format. while the measured current is below the ocv threshold level, the ds2786b actively searches for a relaxed cell by calculating the change in cell voltage as reported in the voltage register over 7.5min intervals (dv/dt). if the 7.5min dv/dt change of an average of four voltage register readings is less than the value stored in the ocv dv/dt threshold register, the ds2786b deter- mines that the cell is now in a relaxed state and the relative capacity register is adjusted based on the ocv cell model stored in parameter eeprom. this operation occurs repeatedly every 7.5min up to 1hr after the cell enters a relaxed state. the ocv dv/dt threshold register has a resolution of 0.61mv/7.5min and a range from 0mv/7.5min to 9.15mv/7.5min. the factory default value is 2.44mv/7.5min. note 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 shows the ocv dv/dt threshold register format. address 7ah 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 78.125%/vh figure 11. initial capacity scaling 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 figure 12. learned capacity scaling factor register format address 7bh 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 25v/r sns figure 13. ocv threshold register format address 7ch smod ldis vodis itemp 2 3 2 2 2 1 2 0 msb lsb units: 0.61mv/7.5min figure 14. ocv dv/dt threshold register format downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge ______________________________________________________________________________________ 13 ocv cell model the ocv cell model is a 9-point piece-wise linearapproximation of open-circuit cell voltage vs. the remaining capacity of the cell. whenever an ocv update occurs, the relative capacity register is adjust- ed to a new value based on the ocv voltage reading and a linear approximation of the table values. figure 15 shows the factory-default cell model stored in eeprom. the ocv cell model can be modified by changing the capacity 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 other- wise can be written to any value between 0.5% to 99.5%. capacity 8 is fixed at a value of 100% and can- not be changed. see figure 16. voltage breakpoints require 2 bytes per breakpoint, but are otherwise stored in a similar manner: voltage break- point 0: msb stored at address 68h, lsb stored at address 69h. other voltage breakpoints are stored sequentially through address location 79h. each volt- age breakpoint has a resolution of 1.22mv, and a range from 0.0v to 4.996v. voltage breakpoint values must also be monotonic. figure 17 is the voltage breakpoint register format. 3.0 3.2 3.4 3.6 3.8 4.0 4.2 0% 20% 40% 60% 80% 100% breakpoint 8 4.171v 100% breakpoint 6 4.042v 85% breakpoint 5 4.005v 80% breakpoint 3 3.752v 25% breakpoint 1 3.619v 5% breakpoint 0 3.186v 0% breakpoint 7 4.087v 90.5% breakpoint 4 3.831v 52.5% breakpoint 2 3.673v 10% figure 15. ds2786bg-c3 ocv cell model address 61hC67h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 0.5% figure 16. capacity 1 to capacity 7 registers format downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 14 ______________________________________________________________________________________ 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 figure 17. voltage breakpoint 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, x: reserved units: 1.22mv figure 18. initial voltage register format address 16h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 0.5% figure 19. last ocv register format initial capacity estimation the ds2786b calculates relative capacity immediatelyupon power-up. during initialization, the ds2786b 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 is removed at the next ocv adjustment. the initial volt- age measurement used in determining the starting point is stored in the initial voltage register until the ic is power cycled. see figure 18. new capacity learning as the cell ages, the initial capacity scaling factorregister value might no longer accurately reflect the true capacity of the cell, causing error in relative capaci- ty calculation while in coulomb-counting mode of opera- tion. the ds2786b has a learn feature that allows the ic to remain accurate as the cell changes. the ds2786b compares the percent relative capacity differencebetween the last two ocv updates to the change in the coulomb count to learn the new cell capacity. the last ocv register maintains the relative capacity percent- age at the previous ocv adjustment point used for learning the new cell capacity. the last ocv is updated with a new value at each ocv adjustment. figure 19 shows the last ocv register format. example: assuming a 15m sense resistor, the ds2786b adjusts the relative capacity of a 1000mahcell 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 multiplied by the learned capacity scal- ing factor value of 55h. the next ocv adjustment deter- mines the relative capacity should actually be at 65%, not 60%. the ds2786b then adjusts the learned capac- ity scaling factor value upward to (65% - 10%)/(500mah x 0.015 ) = 5eh, lowering the expected cell capacity by approximately 10%. downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge ______________________________________________________________________________________ 15 the learn delta percent threshold allows the applicationto select how large a cell capacity change is required before the new cell-capacity value is learned. the dif- ference 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 from adding error to the learned cell-capacity value. it is recom- mended this register be set to a value of at least 50%. figure 20 shows the learn delta percent threshold. memory map the ds2786b has memory space with registers for instru-mentation, status, and control. when the msb of a 2-byte register is read, both the msb and lsb are latched and held for the duration of the read data command to pre- vent updates during the read and ensure synchronization between the 2 register bytes. for consistent results, always read the msb and the lsb of a 2-byte registerduring the same read data command sequence. memory locations 60h through 7fh are eeprom stor- age locations. eeprom memory is shadowed by ram to eliminate programming delays between writes and to allow the data to be verified by the host system before being copied to eeprom. the read data and write data protocols to/from eeprom memory addresses access the shadow ram. setting the rcall bit in the command register (feh) initiates data transfer from the eeprom to the shadow ram. see figure 21. setting the copy bit in the command register initiates data transfer from the shadow ram to the eeprom. an external voltage supply must be provided on the v prog pin prior to writing the copy bit. the ds2786b requires the copy bit be reset to zero within the t prog time window to properly program eeprom. resettingcopy too soon might prevent a proper write of the cells. resetting copy too late might degrade eeprom copy endurance. the ds2786b uses shadow ram data for fuel-gauge calculations. fuel-gauge information can be changed in the application by writing the shadow ram locations. afterwards, the socv bit should be written to reset the fuel gauge. note that any reset of the ic causes the shadow ram data to be restored from eeprom. address 7eh 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 0.5% figure 20. learn delta percent threshold shadow eeprom write recall copy read serial interface figure 21. eeprom access through shadow ram downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 16 ______________________________________________________________________________________ address 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 address description read/write 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 3. memory map addresss description factory value 60h current offset bias register 00h 61h capacity 1 0ah 62h capacity 2 14h 63h capacity 3 32h 64h capacity 4 69h 65h capacity 5 a0h 66h capacity 6 aah 67h capacity 7 b5h 68h voltage breakpoint 0 msb a3h 69h voltage breakpoint 0 lsb 20h 6ah voltage breakpoint 1 msb b9h 6bh voltage breakpoint 1 lsb 50h 6ch voltage breakpoint 2 msb bch 6dh voltage breakpoint 2 lsb 10h 6eh voltage breakpoint 3 msb c0h 6fh voltage breakpoint 3 lsb 20h address description factory value 70h voltage breakpoint 4 msb c4h 71h voltage breakpoint 4 lsb 20h 72h voltage breakpoint 5 msb cdh 73h voltage breakpoint 5 lsb 10h 74h voltage breakpoint 6 msb ceh 75h voltage breakpoint 6 lsb f0h 76h voltage breakpoint 7 msb d1h 77h voltage breakpoint 7 lsb 40h 78h voltage breakpoint 8 msb d5h 79h voltage breakpoint 8 lsb 90h 7ah initial capacity scaling 80h 7bh ocv current threshold 06h 7ch ocv dv/dt threshold 94h 7dh i 2 c address configuration* 60h* 7eh learn threshold 78h 7fh user eeprom 00h table 4. parameter eeprom memory block * 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 register as illustrated in figures 24 and 25. downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge ______________________________________________________________________________________ 17 status/config register the status/config register is read/write with individualbits designated as read only. bit values indicate status as well as program or select device functionality. bits 3 though 6 are eeprom backed at memory location 7ch. note that their bit positions differ between these locations. see figure 22: porf ?he power-on-reset flag is set to indicate initial power-up. porf is not cleared internally. theuser must write this flag value to a zero in order to use it to indicate subsequent power-up events. por event causes a reset of the fuel gauge. porf is read/write-to-zero. smod ?leep mode enable. a value of 1 allows the ic to enter sleep mode when scl and sda are low for t sleep . a value of zero disables the transition to sleep mode. this bit is eeprom backed by bit 7 ofmemory location 7ch. the factory-programmed value is 1. caution: smod sleep feature must be disabled when a battery is charged on an external chargerthat does not connect to the sda or scl pins. smod sleep can be used if the charger pulls sda or scl high. the ic remains in sleep on a charger that fails to properly drive sda or scl and therefore does not adjust relative capacity when a battery is charged. ldis ?earn disable. a value of 1 disables cell- capacity learning by the ic. a value of zero allowscell-capacity learning to occur normally. this bit is eeprom backed by bit 6 of memory location 7ch. the factory-programmed value is zero. vodis ? out disable. a value of 1 disables the v out output. when set to zero, this output is driven t pre before the ain0 conversion begins, and dis- abled after the ain1 conversion ends. this bit iseeprom backed by bit 5 of memory location 7ch. the factory-programmed value is zero. itemp ?temp. a value of 1 enables measurement of temperature using the internal sensor during theain1 conversion timeslot. the ain1 input is not selected and v out is not enabled during the ain1 timeslot. a value of zero restores the measurementof ain1 and enables v out during the ain1 timeslot. this bit is eeprom backed by bit 4 of memorylocation 7ch. the factory-programmed value is 1. ain1 ?in1 conversion valid. this read-only bit indicates that the v out output was enabled and a conversion has occurred on the ain1 pin. whenusing the vodis bit, before reading the ain1 registers, read the ain1 bit. only once the ain1 bit is set should the ain1 register be read. ain0 ?in0 conversion valid. this read-only bit indicates that the v out output was enabled and a conversion has occurred on the ain0 pin. whenusing the vodis bit, before reading the ain0 registers, read the ain0 bit. only once the ain0 bit is set should the ain0 register be read. command register the command register is read/write accessible. bit val-ues indicate operations requested to be performed by the device. see figure 23 for the command 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 x r e s e r v e d . figure 22. status/config register format address feh bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 por 1 x x pocv socv rcall copy 1 bit always reads logic 1. x r e s e r v e d . figure 23. command register format downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 18 ______________________________________________________________________________________ copy ?he copy bit is set to start a copy command of the scratchpad to eeprom. a programming volt-age must be present on the v prog pin prior for the copy to be successful. the copy bit must be clearedby software within the t prog time window. rcall ?he recall bit is set to recall the contents of eeprom into the scratchpad. socv ?tored ocv calculation. this command can be used to reset the relative capacity calculationafter updating ocv cell model data in the scratch- pad. when set to 1, 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 scratchpad. writing the bit to 1 forces a calculation. forcing an ocv calculation creates capacity-estimation error. the bit is cleared when the hardware completes the calculation. pocv ?resent ocv calculation. when set to 1, the part is performing an ocv calculation based onthe voltage stored in the voltage register and the ocv lookup table values present in the scratchpad. writing the bit to 1 forces a calculation. this func- tion should be used for test purposes only. forcing an ocv calculation creates capacity-estimation error. the bit is cleared when the hardware com- pletes the calculation. por ?ower-on reset. a value of 1 starts a power- on reset event. the bit is cleared on the next start orstop on the 2-wire bus, exiting the reset state. user eeprom location 7fh provides 1 byte available for storage ofuser-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 operation as a slave-only device in a single or multislave, and single or multi- master system. the 2-wire interface consists of a serial data line (sda) and serial clock line (scl). sda and scl provide bidirectional communication between the ds2786b slave device and a master device at speeds up to 400khz. the ds2786b? sda pin operates bidi- rectionally; that is, when the ds2786b receives data, sda operates as an input, and when the ds2786b returns data, sda operates as an open-drain output, with the host system providing a resistive pullup. the ds2786b always operates 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 clockcycle, with the cycle defined by scl transitioning low to high and then high to low. the sda logic level must remain stable during the high period of the scl clock pulse. any change in sda when scl is high is inter- preted as a start or stop control signal. bus idle the bus is defined to be idle, or not busy, when nomaster device has control. both sda and scl remain high when the bus is idle. the stop condition is the proper method to return the bus to the idle state. start and stop conditions the master initiates transactions with a start condi-tion (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 sys- tems, 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 anacknowledge bit (a) or a no acknowledge bit (n). both the master and the ds2786b slave generate acknowledge bits. to generate an acknowledge, the receiving device must pull sda low before the rising edge of the acknowledge-related clock pulse (ninth pulse) and keep it low until scl returns low. to gener- ate a no acknowledge (also called nak), the receiver releases sda before the rising edge of the acknowl- edge-related clock pulse and leaves sda high until scl returns low. monitoring the acknowledge bits allows for detection of unsuccessful data transfers. an unsuccessful 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 reattempt communication. data order a byte of data consists of 8 bits ordered msb first. thelsb of each byte is followed by the acknowledge bit. the ds2786b registers composed of multibyte values are ordered msb first. the msb of multibyte registers is stored on even data memory addresses. downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge ______________________________________________________________________________________ 19 slave address a bus master initiates communication with a slavedevice by issuing a start condition followed by a slave address (saddr) and the read/write (r/w) bit. when the bus is idle, the ds2786b continuously moni- tors for a start condition followed by its slave address. when the ic receives an address that match- es its slave address, it responds with an acknowledge bit during the clock period following the r/w bit. the ds2786bg-c3 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 register at location 7dh. read/write bit the r/w bit following the slave address determines thedata direction of subsequent bytes in the transfer. r/w = 0 selects a write transaction, with the following bytes being written by the master to the slave. r/w = 1 selects a read transaction, with the following bytes being read from the slave by the master. with the addr3?ddr0 bits at their default of 0110, writes occur using address 0x6ch, while reads occur at 0x6dh. bus timing the ds2786b is compatible with any bus timing up to400khz. no special configuration is required to operate at any speed. 2-wire command protocols the command protocols involve several transaction for-mats. the simplest format consists of the master writing the start bit, slave address, and r/w bit, and then monitoring the acknowledge bit for presence of the ds2786b. more complex formats such as the write data, read data, and function command protocols write data, read data, and execute device-specific opera- tions. all bytes in each command format require the slave or host to return an acknowledge bit before con- tinuing with the next byte. each function command defi- nition outlines the required transaction format. table 5 applies to the transaction formats. address 7dh bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 addr3 addr2 addr1 addr0 x x x x x reserved. addr3:0 user-adjustable bits of the ds2786bg-c3s i 2 c address. factory default is 0110. figure 24. i 2 c address configuration register 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 figure 25. ds2786b i 2 c address byte format key description s start bit saddr slave address (7 bit) fcmd function command byte maddr memory address byte data data byte written by master a acknowledge bitmaster n no acknowledgemaster key description sr repeated start w r/w bit = 0 r r/w bit = 1 p stop bit data data byte returned by slave a acknowledge bitslave n no acknowledgeslave table 5. 2-wire protocol key downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge 20 ______________________________________________________________________________________ basic transaction formats write: s saddr w a maddr a data0 a p a write transaction transfers 1 or more data bytes to theds2786b. the data transfer begins at the memory address supplied in the maddr byte. control of the sda signal is retained by the master throughout the transac- tion, except for the acknowledge cycles. a read transaction transfers 1 or more bytes from the ds2786b. read transactions are composed of two parts? write portion followed by a read portion?nd are therefore inherently longer than a write transaction. the write portion communicates the starting point for the read operation. the read portion follows immediate- ly, beginning with a repeated start, slave address with r/w set to 1. control of sda is assumed by the ds2786b beginning with the slave address acknowledge cycle. control of the sda signal is retained by the ds2786b throughout the transaction, except for the acknowledge cycles. the master indi- cates the end of a read transaction by responding to the last byte it requires with a no acknowledge. this signals the ds2786b that control of sda is to remain with the master following the acknowledge clock. write data protocol the write data protocol is used to write to register andshadow ram data to the ds2786b starting at memory address maddr. data0 represents the data written to maddr, data1 represents 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 maddrcan be written immediately after the maddr byte is acknowledged. because the address is automatically incremented after the lsb of each byte is received by the ds2786b, the msb of the data at address maddr + 1 can be written immediately after the acknowledgmentof the data at address maddr. if the bus master contin- ues an autoincremented write transaction beyond address 4fh, the ds2786b ignores the data. data is also ignored on writes to read-only addresses and reserved addresses, as well as a write that autoincre- ments to the function command register (address feh). incomplete bytes and bytes that are not acknowl- edged by the ds2786b are not written to memory. as noted in the memory map section, writes to eeprom locations modify the shadow ram only. read data protocol the read data protocol is used to read register andshadow ram data from the ds2786b starting at memo- ry address specified by maddr. data0 represents the data byte in memory location maddr, data1 represents the data from maddr + 1, and datan represents the last byte read by the master: s saddr w a maddr a sr saddr r a data0 a data1 ...datan n p data is returned beginning with the msb of the data inmaddr. because the address is automatically incre- mented after the lsb of each byte is returned, the msb of the data at address maddr + 1 is available to the host immediately after the acknowledgment of the data at address maddr. if the bus master continues to read beyond address ffh, the ds2786b 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 . note that a ?? ?? or ??in the package code indicates rohs status only. packagedrawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. read: saddr w a maddr a sr saddr r a data0 n p write portion read portion package type package code document no. 10 tdfn t1033+1 21-0137 downloaded from: http:///
ds2786b stand-alone ocv-based fuel gauge maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim 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 ____________________ 21 2010 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 7/08 initial release 1 4/10 changed the maximum operating voltage on v dd to 4.5v in the featres , electrical characteristics , and pin description sections 1C5 downloaded from: http:///

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