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1 of 38 rev: 071107 general description the DS2784 operates from 2.5v to 4.6v for integration in battery packs using a single lithium-ion (li+) or li+ polymer cell. available capacity is reported in mah and as a percentage. safe operation is ensured with the included li+ protection function and sha-1-based challenge-response authentication. precision measurements of voltage, temperature, and current, along with cell characteristics and application parameters are used to estimate capacity. the available capacity registers report a conservative estimate of the amount of charge that can be removed given the current temperature and discharge rate. in addition to the nonvolatile (nv) storage for cell compensation and application parameters, 16 bytes of eeprom memory is made available for the exclusive use of the host system and/ or pack manufacturer. this facilitates battery lot and date tracking or nv storage of system or battery usage statistics. a 1-wire ? interface provides serial communication at 16kbps or 143kbps to access data registers, control registers, and user memo ry. additionally, 1-wire communication enables challenge-response pack authentication using sha-1 as the hash algorithm in a hash-based message authentication code (hmac) authentication protocol. applications smartphones/pdas digital still and video cameras cordless voip phones portable gps navigation modes and commands are capitalized for clarity. 1-wire is a registered trademark of dallas semiconductor, a wholly owned subsidiary of maxim integrated products, inc. features ? precision voltage, temperature, and current measurement system ? available capacity estimated from coulomb count, discharge rate, temperature, and cell characteristics ? estimates cell aging using learn cycles ? uses low-cost sense resistor ? allows for calibration of gain and temperature coefficient ? li+ safety circuitry?overvoltage, undervoltage, overcurrent, short-circuit protection ? programmable safety thresholds for overvoltage and overcurrent ? authentication using sha-1 algorithm and 64-bit secret ? 32-byte parameter eeprom ? 16-byte user eeprom ? dallas 1-wire interface with 64-bit unique id ? tiny, pb-free, 14-pin tdfn package embeds easily in battery packs using thin prismatic cells pin configuration ordering information part temp range top mark pin package DS2784g+ -40c to +85c DS2784 14 tdfn (3mm x 5mm) DS2784g+t&r -40c to +85c DS2784 14 tdfn (3mm x 5mm) + denotes a lead-free package. t&r = tape and reel DS2784 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication www.maxim-ic.com
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 2 of 38 absolute maximum ratings voltage range on pls pin relative to v ss -0.3v to +18v voltage range on cp pin relative to v ss -0.3v to +12v voltage range on dc pin relative to v ss -0.3v to (cp + 0.3v) voltage range on cc pin relative to v ss v dd - 0.3v to cp + 0.3v voltage range on all other pins relative to v ss -0.3v to +6.0v maximum voltage range on v in pin relative to v dd v dd + 0.3v continuous sink current, pio, dq 20ma continuous sink current, cc, dc 10ma operating temperature range -40c to +85c storage temperature range -55c to +125c soldering temperature (10s ) see ipc/jedec j-std-020 * this is a stress rating only and functional operation of the device at these or any other conditions above t hose indicated in t he operation sections of this specification is not im plied. exposure to absolute maximum rating co nditions for extended periods of time may affect reliability. electrical characteristics (v dd = 2.5v to 4.6v, t a = -20 c to +70 c, unless otherwise noted. typical values are at t a = +25 c.) parameter symbol conditions min typ max units supply voltage v dd (note 1) 2.5 4.6 v i dd0 sleep mode 1 4 i dd1 sleep mode, v dd = 2.5v 0 c to +50 c 0.4 1.5 i dd2 active mode 85 125 a supply current i dd3 active mode during sha computation 300 500 a temperature accuracy -3 +3 temperature resolution 0.125 temperature range -128.000 +127.875 o c 4.0 v in 4.6, v in v dd + 0.3v -30 30 voltage accuracy, v in 2.5 v in 4.6v, v in v dd + 0.3v -50 +50 mv voltage resolution, v in 4.88 mv voltage range, v in 0 4.99 v input resistance, v in 15 m current resolution 1.56 v current full scale -51.2 +51.2 mv current gain error -1 +1 % full scale current offset (notes 2, 3, 4) -15 +25 v accumulated current offset (notes 2, 3, 4) -360 0 vh/day 0oc t a +50oc -2 +2 time base error -3 +3 % cp output voltage v cp i cc + i dc = 0.9a 8.50 9.25 10.00 v cp startup time t scp ce = 0, de = 0, c cp = 0.1f, active mode 200 ms output high: cc, dc v ohcc v ohdc i oh = -100a (note 5) v cp - 0.4 v output low: cc v olcc i ol = 100a v dd + 0.1 v output low: dc v oldc i ol = 100a 0.1 v
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 3 of 38 parameter symbol conditions min typ max units dq, pio voltage range -0.3 +5.5 v dq, pio input-logic high v ih 1.5 v dq, pio input-logic low v il 0.6 v dq, pio output-logic low v ol iol = 4ma 0.4 v dq, pio pullup current i pu sleep mode, v pin = v dd - 0.4v 0.2 a dq, pio pulldown current i pd active mode, v pin = 0.4v 0.2 a dq input capacitance c dq 50 pf dq sleep timeout t sleep dq < v il 2 9 s pio, dq wake debounce t wdb sleep mode 100 ms sha-1 computation timing computation time t sha 30 ms electrical characteristics: protection circuit (v dd = 2.5v to 4.6v, t a = 0 c to +50 c, unless otherwise noted. typical values are at t a = +25 c.) parameter symbol conditions min typ max units v ov = 11000b 4.457 4.482 4.507 overvoltage detect v ov v ov = 00011b 4.252 4.277 4.302 v charge-enable voltage v ce relative to v ov -75 -100 -125 mv undervoltage detect v uv 2.40 2.45 2.50 v oc = 11b -57 -72 -87 overcurrent detect: charge v coc oc = 00b -15.5 -23.5 -31.5 mv oc = 11b 76 96 116 overcurrent detect: discharge v doc oc = 00b 23.5 35.5 47.5 mv sc = 1b 240 300 360 mv short-circuit current detect v sc sc = 0b 120 150 180 mv overvoltage delay t ovd (note 6) 425 1150 ms undervoltage delay t uvd (notes 6, 7) 84 680 ms overcurrent delay t ocd 8 10 12 ms short-circuit delay t scd 80 120 160 s test threshold v tp coc, doc conditions 0.5 1.0 1.5 v test current i tst sc, coc, doc condition 10 20 40 a pls pulldown current i ppd sleep mode 100 200 600 a recovery current i rc vuv condition, max: v pls = 15v, v dd = 1v min: v pls = 4.2v, v dd = 2v 2.5 5.0 10.00 ma
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 4 of 38 eeprom reliability specification (v dd = 2.5v to 5.5v, t a = -20 c to +70 c, unless otherwise noted.) parameter symbol conditions min typ max units eeprom copy time t eec 10 ms eeprom copy endurance n eec t a = +50c 50,000 cycles electrical characteristics: 1-wire interface, standard (v dd = 2.5v to 5.5v, t a = -20 c to +70 c, unless otherwise noted.) parameter symbol conditions min typ max units time slot t slot 60 120 s recovery time t rec 1 s write-0 low time t low0 60 120 s write-1 low time t low1 1 15 s read-data valid t rdv 15 s reset-time high t rsth 480 s reset-time low t rstl 480 960 s presence-detect high t pdh 15 60 s presence-detect low t pdl 60 240 s electrical characteristics: 1-wire interface, overdrive (v dd = 2.5v to 5.5v, t a = -20 c to +70 c.) parameter symbol conditions min typ max units time slot t slot 6 16 s recovery time t rec 1 s write-0 low time t low0 6 16 s write-1 low time t low1 1 2 s read-data valid t rdv 2 s reset-time high t rsth 48 s reset-time low t rstl 48 80 s presence-detect high t pdh 2 6 s presence-detect low t pdl 8 24 s note 1: all voltages are referenced to v ss . note 2: factory-calibrated accuracy. higher accuracy can be achieved by in-system calibration by the user. note 3: accumulation bias and offset bias registers set to 00h. nben bit set to 0. note 4: parameters guaranteed by design. note 5: cp pin externally driven to 10v. note 6: overvoltage and undervoltage delays (t ovd , t uvd ) are reduced to 0s if the ov or uv co ndition is detected within 100ms of entering active mode. note 7: t uvd min determined by stepping the voltage on v in from v uv + 250mv to v uv - 250mv.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 5 of 38 typical operating circuit pin description pin name function 1 v dd power-supply input. chip supply input. bypass with 0.1f to v ss . 2 ctg connect to ground 3 v ss device ground. chip ground and battery-side sense resistor input. 4 v in battery voltage-sense input. connect to positive cell terminal through decoupling network. 5, 9, 10 n.c. no connection 6 pls pack plus terminal-sense input. used to det ect the removal of short-circuit, discharge overcurrent, and charge overcurrent conditions. 7 cc charge control. charge fet control output. 8 dc discharge control. di scharge fet control output. 11 dq data input/output. serial data i/o, includes weak pulldown to detect battery disconnect and can be configured as wake input. 12 sns sense resistor connection. pack minus term inal and pack-side sense resistor sense input. 13 cp charge pump output. bypass with 0.1f to v ss . 14 pio programmable i/o pin. can be configured as wake input. pad pad exposed pad. connect to v ss or float.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 6 of 38 detailed description the DS2784 functions as an accurate fuel gauge, li+ prot ector, and sha-1-based authent ication token. the fuel gauge provides accurate estimates of remaining capacit y and reports timely voltage, temperature, and current- measurement data. capacity estimates are calculated fr om a piecewise-linear model of the battery performance over load and temperature, and system parameters for full and empty conditions. the algorithm parameters are user programmable and can be modified in pack. crit ical capacity and aging data are periodically saved to eeprom in case of loss of power d ue to a short circuit or deep depletion. the li+ protection function ensures safe , high-performance operation. nfet pr otection switches are driven with a 9v charge pump that increase gate drive as the ce ll voltage decreases. the high-side topology preserves the ground path for serial communication while eliminating the parasitic charge path formed when the fuel gauge ic is located inside the protection fets in a low-side confi guration. the thresholds for overvoltage, overcurrent, and short-circuit current are user programmable for easy customization to each cell and application. the 32-bit wide sha-1 engine with 64-bit secret and 64- bit challenge words resists brute force and other attacks with financial-level hmac security. the challenge of managi ng secrets in the supply chain is addressed with the compute next secret feature. the uniqu e serial number or rom id can be used to assign a unique secret to each battery. block diagram fuelpack? algorithm power mode control precision analog oscillator 16 byte user eeprom 1-wire interface charge pump vdd vdd_int cp current (vss - sns) temperature voltage (vin - vssa) vin vref DS2784 10-bit + sign adc/mux sns vss pio dq wkp, wkd lithium ion protector pls fet drivers cc dc uv, cd 32 byte parameter eeprom pin drivers and pwr switch control pio logic 15-bit + sign adc control and status registers fuelpack? algorithm
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 7 of 38 power modes the DS2784 has two power modes: active and sleep. on init ial power-up, the DS2784 defaults to active mode. in active mode, the DS2784 is fully functional with m easurements and capacity estimation registers continuously updated. the protector circuit monitors the battery voltage s and current for unsafe co nditions. the protection fet gate drivers are enabled when conditions are deemed safe. also, the sha-1 authentication function is available in active mode. when a sha-1 computation is performed, the supply current increases to i dd3 for t sha . in sleep mode, the DS2784 conserves power by disabling measurement and capacity estimation functions, but preserves register contents. gate drive to the protection fets is disabled in sleep. and the sha-1 authentication feature is not operational. sleep mode is entered under two different conditions: bus low and undervoltage. an enable bit makes entry into sleep optional for each condition. sleep mode is not entered if a charger is connected (v pls > v dd + 50mv) or if a charge current of 1.6mv / r sns is measured from sns to v ss . the DS2784 exits sleep mode upon charger connection and v in v uv or a low to high transition on dq. the bus-low condition, where the dq pin is low for t sleep , indicates pack removal or system shutdown in which the 1-wire bus pullup voltage, v pullup , is not present. the power mode (pmod) bit must be set to enter sleep when a bus-low condition occurs. after the DS2784 enters sleep due to a bus-low condition, it is assumed that no charge or discharge current will flow and that coulomb counting is unnecessary. the second condition to enter sleep is an undervoltage condition, which reduces battery drain due to the DS2784 supply current and prevents over discharging the cell. the DS2784 transitions to sleep if the v in voltage is less than v uv (2.45v typical) and the undervolt age enable (uven) bit is set. the 1-wire bus must be in a static state, that is, with dq either high or low for t sleep . the DS2784 transitions from uven sleep to active mode when dq changes logic state. the DS2784 has the ?power switch? capability for waking the device and enabling the protection fets when the host system is powered down. a simple dry-contact switch on the pio pin or dq pin can be used to wake up the battery pack. the power switch function is enabled usin g the pspio and psdq configuration bits in the control register. when pspio or psdq is set and a sleep condition is satisfied, the pio and dq pins pull high weakly, then become armed to detect a low-going transition. a 100ms debounce period filters out glitches that can be caused when a sleeping battery is inserted into a system. figure 1. sleep mode state diagram
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 8 of 38 control register format all control register bits are read an d write accessible. the control regist er is recalled from parameter eeprom memory at power-up. register bit values can be modified in shadow ram after power-up. power-up default values are saved using the copy data command. address 60h bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 nben uven pmod rnaop 0 pspio psdq x nben ?negative blanking enable. a value of 1 enables blanking of negative current values up to 25 v. a value of 0 disables blanking of negative current s. the power-up default of nben = 0. uven ?undervoltage enable. a value of 1 allows the DS2784 to enter sleep mode when the voltage register value is less than v uv and dq is stable at either logic level for t sleep . a value of 0 disables transitions to sleep mode in an undervoltage condition. pmod ?power mode enable. a value of 1 allows the DS2784 to enter sleep mode when dq is low for t sleep . a value of 0 disables dq related transitions to sleep mode.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 9 of 38 rnaop ?read net address op code. a value of 0 selects 33h as the op code value for the read net address command. a value of 1 selects 39h as the read net address opcode value. 0 ?reserved bit, must be programm ed to 0 for proper operation. pspio ?power-switch pio enable. a value of 1 enables the pio pin as a power-switch input. a value of 0 disables the power-switch input function on pio pin. this control is independent of the psdq state. psdq ?power-switch dq enable. a value of 1 enables the dq pin as a power-switch input. a value of 0 disables the power-switch input function on dq pin. this control is independent of the pspio state. x ?reserved bit. li+ protection circuitry during active mode, the DS2784 constantly monitors sns, v in , and v pls to protect the battery from overvoltage (overcharge), undervoltage (overdischarge), and excessiv e charge and discharge currents (overcurrent, short circuit). table 1 summarizes the conditions that activate the protection circuit, the res ponse of the DS2784, and the thresholds that release the DS2784 from a protection state. table 1. li+ protection conditions and DS2784 responses activation condition threshold delay response (2) release threshold overvoltage v in > v ov t ovd cc off v in < v ce or (v sns > 1.6mv and v in < v ov ) undervoltage v in < v uv t uvd cc off, dc off, sleep mode v pls > v in (3) (charger connected) overcurrent, charge v sns < v coc t ocd cc off, dc off v pls < v dd - v tp (4) (charger removed) overcurrent, discharge v sns > v doc t ocd dc off v pls > v dd - v tp (5) (load removed) short circuit v sns > v sc t scd dc off v pls > v dd - v tp (5) (load removed) note 1: all voltages are with respect to v ss . note 2: cc pin driven to v olcc (v dd ) for cc off response. dc pin driven to v oldc (v ss ) for dc off response. note 3: if v in < v uv when charger connection is detec ted, release is delayed until v in v uv . the recovery charge path provides an internal current limit (i rc ) to safely charge the battery. note 4: with test current i tst flowing from pls to v ss (pulldown on pls) enabled. note 5: with test current i tst flowing from v dd to pls (pullup on pls). overvoltage. if the voltage on v in exceeds the overvoltage threshold (v ov ) for a period longer than overvoltage delay (t ovd ), the cc pin is driven low to shut off the external-c harge fet, and the ov flag in the protection register is set. the dc output remains high during overvoltage to allow discharging. when v in falls below the charge enable threshold, v ce , the DS2784 turns the charge fet on by driving cc high. the ds 2784 drives cc high before v in < v ce if a discharge condition persists with v sns 1.6mv and v in < v ov . undervoltage. if v in drops below the undervoltage threshold (v uv ) for a period longer than undervoltage delay (t uvd ), the DS2784 shuts off the charge and disc harge fets and sets the uv flag in the protection register. if uven is set, the DS2784 also enters sleep mode. the DS2784 provides a current-limit ed recovery charge path (i rc ) from pls to v dd to gently charge severely depleted cells. the recovery charge path is enabled when 0 v dd < (v ov - 100mv). once v dd reaches 2.45v (typ), the DS2784 returns to normal operation and begins monitoring v in . once v in > v uv , the DS2784 transitions from sleep to active mode and the cc and dc outputs are driven high to turn on the charge and discharge fets. overcurrent, charge direction (coc). charge current develops a negative voltage on v sns with respect to v ss . if v sns is less than the charge overcurrent threshold (v coc ) for a period longer than overcurrent delay (t ocd ), the
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 10 of 38 DS2784 shuts off both external fets and sets the coc flag in the protection register. the charge current path is not re-established until the voltage on the pls pin drops below v dd - v tp . the DS2784 provides a pulldown current (i tst ) from pls to v ss to pull pls down in order to detect the removal of the offending charge current source. overcurrent, discharge direction (doc). discharge current develops a positive voltage on v sns with respect to v ss . if v sns exceeds the discharge overcurrent threshold (v doc ) for a period longer than t ocd , the DS2784 shuts off the external discharge fet and sets the doc flag in the protection register. the discha rge current path is not re- established until the voltage on pls rises above v dd - v tp . the DS2784 provides a test current (i tst ) from v dd to pls to pull pls up in order to detect the removal of the offending low-impedance load. short circuit. if v sns exceeds short-circuit threshold v sc for a period longer than short-circuit delay (t scd ), the DS2784 shuts off the external discharge fet and sets t he doc flag in the protection register. the discharge current path is not re-established until the voltage on pls rises above v dd - v tp . the DS2784 provides a test current of value (i tst ) from v dd to pls to pull pls up in order to detect the removal of the short circuit. figure 2. li+ protection ci rcuitry example waveforms summary. all the protection conditions previously describe d are logic anded to affect the cc and dc outputs. cc = ( overvoltage ) and ( undervoltage ) and ( overcurrent, charge direction) and (protection register bit ce) dc = ( undervoltage ) and ( overcurrent, either direction) and ( short circuit ) and (protection register bit de ) protection register format the protection register reports events detected by the li+ safety circuit on bits 2 to 7. bits 0 and 1 are used to disable the charge and discharge fet gate drivers. bits 2 to 7 are set by internal hardware only. bits 2 and 3 are cleared by hardware only. bits 4 to 7 are cleared by writing t he register with a 0 in the bit position of interest. writing
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 11 of 38 a 1 to bits 4 to 7 has no effect on the register. bits 0 and 1 are set on power-up and a transition from sleep to active modes. while in active mode, these bits can be clea red to disable the fet gate drive of either or both fets. setting these bits only turns on the fets if there are no protection faults. address 00h bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 ov uv coc doc cc dc ce de ov ?overvoltage flag. ov is set to indicate that an overvoltage condition has been detected. the voltage on v in has persisted above the v ov threshold for t ov . ov remains set until written to a 0 or cleared by a power-on reset or transition to sleep mode. uv ?undervoltage flag. uv is a read-only mi rror of the uvf flag located in t he status register. uvf is set to indicate that v in < v uv . the uvf bit must be written to 0 to clear uv and uvf. coc ?charge overcurrent flag. coc is set to indicate that an overcurrent cond ition has occurred during a charge. the sense-resistor voltage has persisted above the v coc threshold for t oc . coc remains set until written to a 0, cleared by a power-on reset, or transition to sleep mode. doc? discharge overcurrent flag. doc is set to indicate that an overcurrent conditi on has occurred during a discharge. the sense-resistor voltage has persisted above the v doc threshold for t oc . doc remains set until written to a 0, cleared by a power-on reset, or transition to sleep mode. cc ?charge control flag. cc indicates the l ogic state of the cc pin driver. cc flag is set to indicate cc high. cc flag is cleared to indicate cc low. cc flag is read only. dc ?discharge control flag. dc indicates t he logic state of the dc pin driver. dc flag is set to indicate dc high. dc flag is cleared to indicate dc low. dc flag is read only. ce ?charge enable bit. ce must be set to allow the cc pin to drive the charge fet to the on state. ce acts as an enable input to the safety circuit. if all safety conditi ons are met and ce is set, the cc pin drives to v cp . if ce is cleared, the cc pin is driven low to disable the charge fet. de ?discharge enable bit. de must be set to allow the dc pi n to drive the discharge fet to the on state. de acts as an enable input to the safety circuit. if all safety c onditions are met and de is set, the dc pin drives to v cp . if de is cleared, the dc pin is driven low to disable the charge fet. protector threshold register format the 8-bit threshold register consists of bit fields for se tting the overvoltage threshold, charge overcurrent threshold, discharge overcurrent threshold, and short-ci rcuit threshold for the protection circuit. address 7fh bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 vov4 vov3 vov2 vov1 vov0 sc0 oc1 oc0
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 12 of 38 table 2. vov threshold vov bit field v ov vov bit field v ov 0 0 0 0 0 4.248 1 0 0 0 0 4.404 0 0 0 0 1 4.258 1 0 0 0 1 4.414 0 0 0 1 0 4.268 1 0 0 1 0 4.424 0 0 0 1 1 4.277 1 0 0 1 1 4.434 0 0 1 0 0 4.287 1 0 1 0 0 4.443 0 0 1 0 1 4.297 1 0 1 0 1 4.453 0 0 1 1 0 4.307 1 0 1 1 0 4.463 0 0 1 1 1 4.316 1 0 1 1 1 4.473 0 1 0 0 0 4.326 1 1 0 0 0 4.482 0 1 0 0 1 4.336 1 1 0 0 1 4.492 0 1 0 1 0 4.346 1 1 0 1 0 4.502 0 1 0 1 1 4.356 1 1 0 1 1 4.512 0 1 1 0 0 4.365 1 1 1 0 0 4.522 0 1 1 0 1 4.375 1 1 1 0 1 4.531 0 1 1 1 0 4.385 1 1 1 1 0 4.541 0 1 1 1 1 4.395 1 1 1 1 1 4.551 table 3. coc, doc threshold oc[1:0] bit field v coc (mv) v doc (mv) 0 0 -23.5 35.5 0 1 -36 48 1 0 -48 72 1 1 -72 96 table 4. sc threshold sc0 bit field v sc (mv) 0 150 1 300 voltage measurement battery voltage is measured every 440ms on the v in pin with respect to v ss . measurements have a 0 to 4.99v range and a 4.88mv resolution. the value is stored in the voltage register in two?s complement form and is updated every 440ms. voltages above the maximum register value are reported at the maximum value; voltages below the minimum register value are reported at the minimum value. voltage register format msb?address 0ch lsb?address 0dh 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: 4.886mv
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 13 of 38 temperature measurement the DS2784 uses an integrated temperature sensor to m easure battery temperature with a resolution of 0.125c. temperature measurements are updated every 440ms and plac ed in the temperature register in two?s complement form. temperature register format msb?address 0ah lsb?address 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 note: temperature and battery voltage (v in ) are measured using the same adc. theref ore, measurements are a 220ms average updated every 440ms. current measurement the DS2784 continually measures the curr ent flow into and out of the battery by measuring the voltage drop across a low-value current-sense resistor, r sns . the voltage-sense range between sns and v ss is 51.2mv. the input linearly converts peak-signal amplitudes up to 102.4mv as long as the continuous signal level (average over the conversion cycle period) does not exc eed 51.2mv. the adc samples the i nput differentially at 18.6khz and updates the current register at the completion of eac h conversion cycle (3.52s). charge currents above the maximum register value are reported as 7fffh. discharge currents below the minimum register value are reported as 8000h. current register format msb?address 0eh lsb?address 0fh s 2 14 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb msb lsb ?s?: sign bit(s) units: 1.5625 v/r sns the average current register reports an average current level over the precedi ng 28s. the register value is updated every 28s in two?s complement form, and represents an average of the eight preceding current register values. average current register format msb?address 08h lsb?address 09h s 2 14 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb msb lsb ?s?: sign bit(s) units: 1.5625 v/r sns current offset correction every 1024th conversion, the adc measures its input offset to facilitate offset correction. offset correction occurs approximately once per hour. the resulting correction fa ctor is applied to the subsequent 1023 measurements. during the offset correction conversi on, the adc does not measure the sens e-resistor signal. a maximum error of 1/1024 in the accumulated current regi ster (acr) is possible; however, to reduce the error, the current
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 14 of 38 measurement made just prior to the offset conversion is retained in the current register and is substituted for the dropped current measurement in the curr ent accumulation process. therefore, the accumulated current error due to offset correction is typi cally much less than 1/1024. current offset bias the current offset bias (cob) value allows a programmabl e offset value to be added to raw current measurements. the result of the raw current measurem ent plus cob is displayed as the current measurement result in the current register, and is used for current accumulation. cob can be us ed to correct for a static offset error, or can be used to intentionally skew the current results a nd, therefore, the current accumulation. read and write access is allowed to cob. whenever the cob is written, the new value is applied to all subsequent current measurements. cob can be programmed in 1.56 v steps to any value betw een +198.1v and -199.7v. the cob value is stored as a two?s complement value in eeprom. the cob is loaded on power-up from eeprom memory. the factory default value is 00h. the difference between the cab and cob is that the cab is not subject to current blanking. offset currents between 100v and -25v are not accumulated if the offset is made by the cob. offset currents between 100v and -25v are accumulated if they are made by the cab. current offset bias register format address 7bh s 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb ?s?: sign bit(s) units: 1.56 v/r sns current blanking the current blanking feature modifies current measurement result prior to being accumu lated in the acr. current blanking occurs conditionally when a current measurem ent (raw current + cobr) falls in one of two defined ranges. the first range prevents charge currents less than 100 v from being accumulated. the second range prevents discharge currents less than 25 v in magnitude from being accumula ted. charge current blanking is always performed; however, discharge current blanking must be enabled by setting the nben bit in the control register. see the register descri ption for additional information.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 15 of 38 current measurement calibration the DS2784?s current measurement gain can be adjusted through the rsgain register, which is factory calibrated to meet the data sheet-specified accu racy. rsgain is user accessible and can be reprogrammed after module or pack manufacture to improve the current measurement accura cy. adjusting rsgain can correct for variation in an external sense resistor?s nominal value, and allows the use of low-cost, nonprecision, current-sense resistors. rsgain is an 11-bit value stored in 2 bytes of the par ameter eeprom memory block. the rsgain value adjusts the gain from 0 to 1.999 in steps of 0.001 (precisely 2 -10 ). the user must program rsgain cautiously to ensure accurate current measurement. when shipped from the factory, the gain calibration value is stored in two separate locations in the parameter eeprom block: rsgain, whic h is reprogrammable, and frsgain, which is read only. rsgain determines the gain used in the current measurem ent. the frsgain value is provided to preserve the factory calibration value only and is not used to calibrate the current measurement. the 16-bit frsgain value is readable from addresses b0h and b1h. current measurement ga in register format msb?address 78h lsb?address 79h x x x x x 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb msb lsb units: 2 -10 sense resistor tempe rature compensation the DS2784 can of temperature compensate the current-sense resistor to correct for variation in a sense resistor?s value overtemperature. the DS2784 is factory programmed with the sense-resistor temperature coefficient, rstc, set to zero, which turns off the temperature compensa tion function. rstc is user accessible and can be reprogrammed after module or pack manufacture to impr ove the current accuracy when using a high-temperature coefficient current-sense resistor. rstc is an 8-bit va lue stored in the parameter eeprom memory block. the rstc value sets the temperature coefficient from 0 to +7782ppm/oc in steps of 30.5ppm/oc. the user must program rstc cautiously to ensure accurate current measurement. temperature compensation adjustments are made when the temperature register crosses 0.5 o c boundaries. the temperature compensation is most effective with th e resistor placed as close as possible to the v ss terminal. this optimizes thermal coupling of the resistor to the on-chip temperature sensor. sense resistor temperature com pensation register format address 7ah 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 30.5ppm/oc current accumulation current measurements are internally summed, or accu mulated, at the completion of each conversion period and the results are stored in the acr. the accuracy of the acr is depende nt on both the current measurement and the conversion time base. the acr has a range of 0 to 409.6mvh with an lsb of 6.25 vh. additional registers hold fractional results of each accumulation to avoid truncation errors. the fractional result bits are not user accessible. accumulation of charge current above the maximum register value is reported at the maximum value; conversely, accumulation of discharge current below the minimum register value is reported at the minimum value. charge currents (positive current register values) less than 100 v are not accumulated in order to mask the effect of accumulating small positive offset errors over long periods. this limits the minimum charge current, for coulomb- counting purposes, to 5ma for r sns = 0.020 and 20ma for r sns = 0.005 .
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 16 of 38 read and write access is allowed to the acr. the acr mu st be written msb first then lsb. whenever the acr is written, the fractional accumulation result bits are cl eared. the write must be completed in 3.5s (one acr update period). a write to the acr forces the adc to perform an offs et correction conversion and update the internal offset correction factor. the current measurement and accumulation begin with the second conversion following a write to the acr. the acr value is backed up to eeprom in case of power loss. the acr value is recovered from eeprom on power-up. see table 8 for specific address location and backup frequency. accumulated current register format msb?address 10h lsb?address 11h 2 15 2 14 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb msb lsb units: 6.25 vh/r sns table 5. resolution and ra nge vs. sense resistor r sns v ss - v sns 20m 15m 10m 5m current resolution 1.5625 v 78.13 a 104.2 a 156.3 a 312.5 a current range 51.2mv 2.56a 3. 41a 5.12a 10.24a acr resolution 6.25 vh 312.5 ah 416.7 ah 625 ah 1.250mah acr range 409.6mvh 20.48ah 27. 31ah 40.96ah 81.92ah accumulation bias in some designs a systematic error or an application preference requires the ap plication of an arbitrary bias to the current accumulation process. the current accumulation bi as register (cab) allows a user-programmed constant positive or negative polarity bias to be included in the cu rrent accumulation process. the value in cab can be used to estimate battery currents that do not flow through the se nse resistor, estimate battery self-discharge or estimate current levels below the current measurement resolution. the user programmed two?s complement value, with bit weighting the same as the current register, is added to the acr once per current conv ersion cycle. the cab is loaded on power-up from eeprom memory. the difference between the cab and cob is that the cab is not subject to current blanking. offset currents between 100v and -25v are not accumulated if the offset is made by the cob. offset currents between 100v and -25v are accumulated if they are made by the cab. current accumulation bias register format address 61h s 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb ?s?: sign bit units: 1.5625 v/r sns
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 17 of 38 capacity estima tion algorithm remaining capacity estimation uses real-time meas ured values, stored parameters describing the cell characteristics, and application operating limits. fi gure 2 describes the algorit hm inputs and outputs. figure 2. top-level algorithm diagram modeling cell characteristics to achieve reasonable accuracy in estimating remain ing capacity, the cell performance characteristics overtemperature, load current, and charge-termination point must be considered. since the behavior of li+ cells is nonlinear, these characteristics must be included in the capacity estimation to achieve an acceptable level of accuracy in the capacity estimation. the fuelpack ? method used in the DS2784 is described in general in application note 131: lithium-ion cell fuel gauging with dallas semiconductor battery monitor ics. to facilitate efficient implementation in hardware, a modified version of the method outlined in an131 is used to store cell characteristics in the DS2784. full and empty points are retr ieved in a lookup process which retraces a piece-wise linear model consisting of three model curves named full, active empty, and standby empty. each model curve is constructed with 5-line segments, numbered 1 through 5. above 40c, the segment 5 model curves extend infinitely with zero slope, approximat ing the nearly flat change in capacity of li+ cells at temperatures above 40c. segment 4 of each model curves originates at +40c on it s upper end and extends downward in temperature to the junction with segment 3. segment 3 joins with segment 2, which in turn joins with segment 1. segment 1 of each model curve extends from the junction with segment 2 to infinitely colder temperatures. the three junctions or breakpoints that join the segments (labeled tbp12, t bp23, and tbp34 in figure 3) are programmable in 1c increments from -128c to +40c. the slope or derivative for segments 1, 2, 3, and 4 are also programmable over a range of 0 to 15,555ppm, in steps of 61ppm. fuelpack is a trademark of dallas semiconductor, a wholly owned subsidiary of maxim integrated products, inc. capacity look-up a vailable capacity calculation a cr housekeeping a ge estimato r learn function cell model parameters (eeprom) full(t) (r) a ctive empty (t) (r) standby empty (t) (r) remaining active absolute capacity (raac) mah (r) sense resistor? (rsnsp) (1byte ee) voltage (r) temperature (r) current (r) a ccumulated current (acr) (r/w) user memory (eeprom) 16 bytes a ging cap (ac) (2 bytes ee) charge voltage (vchg) (1 byte ee) remaining standby absolute capacity (rsac) mah (r) remaining active relative capacity (rarc) % (r) remaining standby relative capacity (rsrc) % (r) a ge scalar (as) (1 bytes ee) min chg current (imin) (1 byte ee) empty voltage (vae) (1 byte ee) empty current (iae) (1 byte ee) a verage current (r)
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 18 of 38 figure 3. cell model example diagram full ?the full curve defines how the full point of a given cell va ries over temperature for a given charge termination. the application?s charge termination method should be used to determine the table values. the DS2784 reconstructs the full line from the cell characteristic tabl e to determine the full capacity of the battery at each temperature. reconstruction occurs in one-degree temperature increments. active empty ?the active-empty curve defines the variation of the active-empty point over temperature. the active-empty point is defined as the minimum voltage requi red for system operation at a discharge rate based on a high-level load current (one that is sustained during a high-power oper ating mode). this load current is programmed as the active-empty current (iae), and should be a 3.5s average value to correspond to values read from the current register. the spec ified minimum voltage, or active empty voltage (vae), should be a 220ms average value to correspond to the values read from t he voltage register. the DS2784 reconstructs the active empty line from the cell characteristic table to determi ne the active empty capacity of the battery at each temperature. reconstruction occurs in one-degree temperature increments. standby empty ?the standby-empty curve defines the variation of the standby-empty point over temperature. the standby-empty point is defined as the mi nimum voltage required for standby oper ation at a discharge rate dictated by the application standby current. in typical handheld applications, standby empty represents the point that the battery can no longer support dram refresh and thus t he standby voltage is set by the minimum dram voltage- supply requirements. in other applications, standby empt y can represent the point that the battery can no longer support a subset of the full application operation, such as games or organizer functions. the standby load current and voltage are used for determining the cell characteristic s but are not programmed in to the DS2784. the DS2784 reconstructs the standby-empty line from the cell characte ristic table to determine the standby-empty capacity of the battery at each temperature. reconstructi on occurs in one-degree temperature increments. cell model construction the model is constructed with all poi nts normalized to the fully charged state at +40c. all values are stored in the cell parameter eeprom block. the +40c full value is stored in vhr with an lsb of 6.25vhr. the +40c active empty value is stored as a percentag e of +40c full with a resolution of 2 -10 . standby empty at +40c is, by definition, zero and , therefore , no storage is required. the slopes (der ivatives) of the 4 segments for each tbp12 tbp23 tbp34 40c 100% segment 1 derivative [ppm/c] active empty standby empty full cell characterization data points seg. 2 seg. 3 seg. 4 seg. 5
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 19 of 38 model curve are stored in the cell parameter eeprom block as ppm/c. the breakpoint temperatures of each segment are stored there also (see application note 3584: storing battery fuel gauge parameters in ds2780 for more details on how values are stored). an example of data stored in this manner is shown in table 6. table 6. example cell characterizat ion table (normalized to +40c) manufacturer?s rated cell capacity: 1000mah charge voltage: 4.2v termination current: 50ma active empty (v): 3.0v active empty (i): 300ma sense resistor: 0.020 tbp12 tbp23 tbp34 segment breakpoints -12 c 0 c 18 c +40 c nominal (mah) seg. 1 ppm/ c seg. 2 ppm/ c seg. 3 ppm/ c seg. 4 ppm/ c full 1051 3601 3113 1163 854 active empty 2380 1099 671 305 standby empty 1404 427 244 183 figure 4. lookup function diagram * see result registers section for a description of these registers. application parameters in addition to cell model characteristics, several applicat ion parameters are needed to detect the full and empty points, as well as calculate results in mah units. sense resistor prime (r snsp [1/ ]) ?r snsp stores the value of the sense resistor for use in computing the absolute capacity results. the resistance is stored as a 1-byte conductance value with units of mhos (1/ ) . r snsp supports resistor values of 1 to 3.922m . r sns is located in the parameter eeprom block. r snsp = 1/r sns (units of mhos; 1/ ) charge voltage (vchg) ?vchg stores the charge voltage threshold us ed to detect a fully charged state. the voltage is stored as a 1-byte value with units of 19.5 mv and can range from 0v to 4.978v. vchg should be set marginally less than the cell voltage at the end of the char ge cycle to ensure reliable charge termination detection. vchg is located in the parameter eeprom block. cell model parameters (eeprom) temperature lookup function full(t) * ae(t) * se(t) *
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 20 of 38 minimum charge current (imin) ?imin stores the charge current threshold used to detect a fully charged state. it is stored as a 1-byte value with units of 50 v (imin x r sns ) and can range from 0 to 12.75mv. assuming r sns = 20m , imin can be programmed from 0ma to 637.5ma in 2.5m a steps. imin should be set marginally greater than the charge current at the end of the ch arge cycle to ensure reliable charge termination detection. imin is located in the parameter eeprom block. active empty voltage (vae) ?vae stores the voltage threshold used to detect the active empty point. the value is stored in 1-byte with units of 19.5mv and can range from 0v to 4.978v. vae is located in the parameter eeprom block. see the cell characteristics section for more information. active empty current (iae) ?iae stores the discharge current threshol d used to detect the active empty point. the unsigned value represents the magnitude of the discha rge current and is stored in 1-byte with units of 200 v and can range from 0 to 51.2mv. assuming r sns = 20m , iae can be programmed from 0ma to 2550ma in 10ma steps. iae is located in the parameter eeprom block. see the cell model construction section for more information. aging capacity (ac) ?ac stores the rated cell capacity, which is used to estimate the decrease in battery capacity that occurs during normal use. the value is stored in 2 bytes in the same units as the acr (6.25 vh). when set to the manufacturer?s rated cell capacity the aging estimation rate is approx imately 2.4% per 100 cycles of equivalent full capacity discharges. partial dischar ge cycles are added to form equivalent full capacity discharges. the default aging estimation results in 88% capacity after 500 equivalent cycles. the aging estimation rate can be adjusted by setting the ac to a value other th an the cell manufacturer?s rating. setting ac to a lower value, accelerates the aging estimation rate. setting ac to a higher value, retards the aging estimation rate. the ac is located in the par ameter eeprom block. age scalar (as) ?as adjusts the cell capacity estimation results downward to compensate for aging. the as is a 1-byte value that has a range of 49.2% to 100% . the lsb is weighted at 0.78% (precisely 2 -7 ). a value of 100% (128 decimal or 80h) represents an unaged battery. a value of 95% is recommended as the starting as value at the time of pack manufacture to allow the learning of a larger capacity on batteries that have an initial capacity greater than the rated cell capacity programmed in the cell charac teristic table. the as is modified by aging estimation introduced under aging capacity and by the capacity-learn fu nction. the host system has read and write access to the as, however caution should exerci sed when writing it to ensure that the cumulative aging estimate is not overwritten with an incorrect value. the as is automat ically saved to eeprom (see table 7 for details). the eeprom value is reca lled on power-up. full capacity estimation based on the learn function is more accurate than the cycle-count-based estimation. the learn function reflects the current performance of t he cell. cycle count based estimation is an approximation derived from the manufacturer?s recommendation for a typical cell. batteries are typically considered worn-out when the full capacity reaches 80% of the rated capacity, theref ore, the as value is not required to range to 0%. it is clamped to 50% (64d or 40h). if a value of 50% is read from the as, the host should prompt the user to initiate a learning cycle. capacity estimation operation aging estimation as discussed above, the as register value is adjusted oc casionally based on cumulative discharge. as the acr register decrements during each dischar ge cycle, an internal counter is incremented until equal to 32 times the ac. the as is then decremented by one, resulting in a dec rease of the scaled full battery capacity by 0.78% (approximately 2.4% per 100 cycles). see the ac register description above for recommendations on customizing the age-estimation rate. learn function since li+ cells exhibit charge efficiencies near unity, the ch arge delivered to a li+ cell from a known empty point to a known full point is a dependable measure of the cell capacity. a continuous charge from empty to full results in a learn cycle. first, the active empty poi nt must be detected. the learn flag (learnf) is set at this point. then, once charging starts, the charge must continue uninterrupted until the battery is charged to full. upon detecting full,
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 21 of 38 learnf is cleared, the charge to full (chgtf) flag is set, and the age scalar (as) is adjusted according to the learned capacity of the cell. acr housekeeping the acr value is adjusted occasionally to maintain t he coulomb count within the model curve boundaries. when the battery is charged to full (chgtf set), the acr is set equal to the age scaled full lookup value at the present temperature. if a learn cycle is in progr ess, correction of the acr value occurs after the age scalar (as) is updated. when an empty condition is detected (learnf and/or aef set), the acr adjustment is conditional: ? if the aef is set and the learnf is not set, then the acti ve-empty point was not detected. the battery is likely below the active-empty capacity of the model. the acr is set to the active-empty model value at present temp only if it is greater than the active-e mpty model value at present temp. ? if the aef is set, the learnf is not set, and the acr is below the active-empty model value at present temp the acr is not updated. ? if the learnf is set, then the battery is at the active-e mpty point and the acr is set to the active-empty model value. full detect full detection occurs when the voltage (v) readings re main continuously above the charge voltage (vchg) threshold for the duration of two av erage current (iavg) readings, and both iavg readings are below terminating current (imin). the two consecutive iavg readings must also be positive and nonzero (> 16 lsb). this ensures that removing the battery from the char ger does not result in a false detection of full. full detect sets the charge to full (chgtf) bit in the status register. active-empty point detect active-empty point detection occurs when the voltage r egister drops below the vae threshold and the two previous current readings are above i ae. this captures the event of the ba ttery reaching the active-empty point. note that the two previous current r eadings must be negative and greater in m agnitude than iae, that is, a larger discharge current than specified by the iae threshold. q ualifying the voltage level with the discharge rate ensures that the active-empty point is not det ected at loads much lighter than those used to construct the model. also, the active-empty point must not be detected when a deep dischar ge at a very light load is followed by a load greater than iae. either case would cause a learn cycle on the fo llowing charge to include part of the standby capacity in the measurement of the active capacity. active-empty point detection sets the learn flag (learnf) bit in the status register. do not confuse the active-empty point with the active-empty flag. the active-empty flag is set only when the vae threshold is passed. status register format the status register contains bits that report the device status. all bits are se t internally. the chgtf, aef, sef, and learnf bits are read only. the uvf and porf bits can be cleared by writing a zero to the bit locations. address 01h bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 chgtf aef sef learnf x uvf porf x chgtf ?charge-termination flag. chgtf is set to indicate that the voltage and average current register values have persisted above the vchg and below the imin thresholds sufficiently long to detect a fully charged condition. chgf is cleared when rarc is less than 90%. chgf is read only. aef ?active-empty flag. aef is set to indicate that the batte ry is at or below the active-empty point. aef is set when the voltage register value is less than the vae th reshold. aef is cleared w hen rarc is greater than 5%. aef is read only. sef ?standby-empty flag. sef is set to indicate rsrc is less than 10%. sef is cl eared when rsrc is greater than 15%. sef is read only.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 22 of 38
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 23 of 38 learnf ?learn flag. learnf indicates that the current charge cycle can be used to l earn the battery capacity. learnf is set when the active-empty point is detected. this occurs when the voltage register value drops below the vae threshold and the two previous current register values were ne gative and greater in magnitude than the iae threshold. see the active-empty point detect section for additional information. learnf is cleared when any of the following occur: 1) learn cycle completes (chgtf set). 2) current register value becomes nega tive indicating discharge current flow. 3) acr = 0 4) acr value is written or recalled from eeprom. 5) sleep mode is entered. learnf is read only. uvf ?undervoltage flag. uvf is set to indicate that the voltage measurement of the v in pin is less than v uv , and must be written to a 0 to allow subsequent undervoltage events to be reported. uvf is not cleared internally. writing uvf to 0 is effective only when v in is greater or equal to v uv , otherwise, uv remains set due to the persistent undervoltage condition. uvf is set on power-up. porf ?power-on reset flag. porf is set to indicate initia l power-up. porf is not cleared internally. the user must write this flag value to a 0 to use it to indicate subsequent power-up events. if porf indicates a power-on reset, the acr could be misaligned with the actual battery st ate of charge. the system c an request a charge to full to synchronize the acr with the battery ch arge state. porf is read/write-to-zero. x ?reserved bits. result registers the DS2784 processes measurement and cell characteristics on a 3.5s interval and yields seven result registers. the result registers are sufficient for di rect display to the user in most appl ications. the host system can produce customized values for system use or user display by combining measurement, result and user eeprom values. full(t) [ ] ?the full capacity of the battery at the present tem perature is reported normalized to the 40c full value. this 15-bit value reflects the cell model full val ue at the given temperature. full(t) reports values between 100% and 50% with a resolution of 61ppm (precisely 2 -14 ). the register is clamped to a maximum value of 100% even though the register format permits values greater than 100%. active empty, ae(t) [ ] ?the active-empty capacity of the battery at the present temperature is reported normalized to the 40c full value. this 13-bit value refl ects the cell model active-empty value at the given temperature. ae(t) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2 -14 ). standby empty, se(t) [ ] ?the standby-empty capacity of the battery at the present temperature is reported normalized to the 40c full value. this 13-bit value refl ects the cell model standby-emp ty value at the current temperature. se(t) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2 -14 ). remaining active absolute capacity (raac) [mah] ?raac reports the remaining battery capacity available under the current temperature conditions to the active-empty point in absol ute units of milliamp-hours (mahr). raac is 16 bits.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 24 of 38 msb?address 02h lsb?address 03h 2 15 2 14 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb msb lsb units: 1.6mahr remaining standby absolute capacity (rsac) [mah] ?rsac reports the remaining battery capacity available under the current temperature conditions to the standby-emp ty point capacity in absolute units of milliamp-hours (mahr). rsac is 16 bits. msb?address 04h lsb?address 05h 2 15 2 14 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb msb lsb units: 1.6mahr remaining active relative capacity (rarc) [%] ?rarc reports the remaining batte ry capacity available under the current temperature conditions to the active-empty point in relative units of percent. rarc is 8 bits. address 06h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 1% remaining standby relative capacity (rsrc) [%] ?rsrc reports the remaining battery capacity available under the current temperature conditions to the standby-empty point c apacity in relative units of percent. rsrc is 8 bits. address 07h 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 msb lsb units: 1%
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 25 of 38 calculation of results raac [mah] = (acr[mvh] - ae(t) * full40[mvh]) * rsnsp [mhos] note: rsnsp = 1/rsns rsac [mah] = (acr[mvh] - se(t) * full40[mvh]) * rsnsp [mhos] note: rsnsp = 1/rsns rarc [%] = 100% * (acr[mvh] - ae(t) * full40[mvh]) / {(as * full(t) - ae(t)) * full40[mvh]} rsrc [%] = 100%* (acr[mvh] - se(t) * full40[mvh]) / {(as * full(t) - se(t)) * full40[mvh]} special feature register format all register bits are read and write accessible, with default values specified in each bit definition. address 15h bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 x x x x x x x piob piob ?pio pin sense and control bit. writing a 0 to the pi ob bit activates the pio pin open-drain output driver, forcing the pio pin low. writing a 1 to piob disables the output driver, allowing the pio pin to be pulled high or used as an input. reading piob returns the logic level forced on the pio pin. note that if the pio pin is left floating with piob set, a weak pulldown curr ent source pulls the pio pin to v ss . piob is set to a 1 on power-up. piob is also set in sleep mode to ensure the pio pin is high-impedance in sleep mode. note: do not write piob to 0 if pspio is enabled. x ?reserved bits. eeprom register the eeprom register provides access control of the eepr om blocks. eeprom blocks can be locked to prevent alteration of data within the block. locking a block disables write access to the block. once a block is locked, it cannot be unlocked. r ead access to eeprom blocks is unaffe cted by the lock/unlock status. eeprom register format address 1fh bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 eec lock x x x x bl1 bl0 eec ?eeprom copy flag. a 1 in this read-only bit indicate s that a copy data functi on command is in progress. while this bit is high, writes to eeprom addresses are ig nored. a 0 value in this bit indicates that data can be written to unlocked eeprom. lock ?eeprom lock enable. when the lock bit is 0, the lock function command is ignored. writing a 1 to this bit enables the lock function command. after setting the lock bit the lock function command must be issued as the next command, or else the lock bit is reset to 0. after the lo ck operation is completed, the lock bit is reset to 0. the lock bit is a volatile r/w bit, initialized to 0 upon por.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 26 of 38 bl1 ?parameter eeprom block 1 lock flag. a 1 in this re ad-only bit indicates that eeprom block 1 (addresses 60h to 7fh) is locked (read only) while a 0 indicates block 1 is unlocked (read/write). bl0 ?user eeprom block 0 lock flag. a 1 in this read-only bit indicates t hat eeprom block 0 (addresses 20h to 2fh is locked (read only) while a 0 indicates block 0 is unlocked (read/write). x ? reserved bits. memory the DS2784 has a 256-byte linear memory space with register s for instrumentation, stat us, and control, as well as eeprom memory blocks to store para meters and user information. byte addresses designated as ?reserved? typically return ffh when read. these bytes should not be wr itten. several byte register s are paired into two-byte registers in order to store 16-bit values. the most significa nt byte (msb) of the 16-bit va lue is located at the even address and the least significant byte (lsb) is located at the next address (odd) byte. when the msb of a two-byte register is read, the msb and lsb are latched simult aneously and held for the duration of the read data command. this prevents updates to the lsb during the re ad ensuring synchronization between the two register bytes. for consistent results, always read the msb and th e lsb of a two-byte register during the same read data sequence. eeprom memory consists of nonvolatile (nv) eeprom ce lls overlaying volatile shadow ram. the read data and write data protocols allow the 1-wire interface to dire ctly accesses the shadow ram only. the copy data and recall data function commands transfer data between the eeprom cells and the shadow ram. in order to modify the data stored in the eeprom cells, data must be written to t he shadow ram and t hen copied to the eerpom. to verify the data stored in the eeprom cells, the eeprom data must be recalled to the shadow ram and then read from the shadow. after issuing the copy data function comma nd, access to the eeprom block is not available until the eeprom copy comple tes, which takes 2ms typically (see t eec in the electrical characteristics table). figure 5. eeprom access via shadow ram user eeprom?block 0 a 16-byte user eeprom memory (block 0, addresses 20h?2fh) provides nv me mory that is uncommitted to other DS2784 functions. accessing the user eeprom block doe s not affect the operation of the DS2784. user eeprom is lockable; once locked, write access is not allowed. the battery pack or host system manufacturer can program lot codes, date codes, and other manufacturing or warranty or diagnostic information and then lock it to safeguard the data. user eeprom can also store parameters for charging to support different size batteries in a host device as well as auxiliary model data such as time to full charge estimation parameters. parameter eeprom?block 1 model data for the cells, as well as a pplication operating parameters, are st ored in the parameter eeprom (block 1, addresses 60h?7fh). the acr (msb and lsb) and as registers are automatic ally saved to eeprom when the rarc result crosses 4% boundaries. this allows t he DS2784 to be located outside the protection fets. serial interface write read shadow ram eeprom copy recall
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 27 of 38 table 7. parameter eeprom memory block address (hex) description address (hex) description 60 control ?control register 70 ae segment 4 slope 61 ab ? accumulation bias 71 ae segment 3 slope 62 ac ?aging capacity msb 72 ae segment 2 slope 63 ac ?aging capacity lsb 73 ae segment 1 slope 64 vchg ?charge voltage 74 se segment 4 slope 65 imin ?minimum charge current 75 se segment 3 slope 66 vae ?active-empty voltage 76 se segment 2 slope 67 iae ?active-empty current 77 se segment 1 slope 68 active empty 40 78 rsgain ?sense resistor gain msb 69 r snsp ?sense resistor prime 79 rsgain ?sense resistor gain lsb 6a full 40 msb 7a rstc ?sense resistor temp coefficient 6b full 40 lsb 7b cob ?current offset bias 6c full segment 4 slope 7c tbp34 6d full segment 3 slope 7d tbp23 6e full segment 2 slope 7e tbp12 6f full segment 1 slope 7f protector threshold register
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 28 of 38 table 8. memory map address (hex) descri ption read/write 00 protection register r/w 01 status register r/w 02 raac msb r 03 raac lsb r 04 rsac msb r 05 rsac lsb r 06 rarc r 07 rsrc r 08 average current register msb r 09 average current register lsb r 0a temperature register msb r 0b temperature register lsb r 0c voltage register msb r 0d voltage register lsb r 0e current register msb r 0f current register lsb r 10 accumulated current register msb r/w * 11 accumulated current register lsb r/w * 12 accumulated current register lsb-1 r 13 accumulated current register lsb-2 r 14 age scalar r/w * 15 special feature register r/w 16 full msb r 17 full lsb r 18 active-empty msb r 19 active-empty lsb r 1a standby-empty msb r 1b standby-empty lsb r 1c to 1e reserved ? 1f eeprom register r/w 20 to 2f user eeprom, lockable, block 0 r/w 38 to 5f reserved ? 60 to 7f parameter eeprom, lockable, block 1 r/w 80 to af reserved ? b0 factory gain rsgain msb r b1 factory gain rsgain lsb r b2 to ff reserved ? * register value is automatically saved to eeprom during active mode operation and recalled from eeprom on power-up.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 29 of 38 authentication authentication is performed using a fips-180-compliant sha-1 one-way hash algorithm on a 512-bit message block. the message block consists of a 64-bit secret, a 64-bit challenge and 384 bits of constant data. optionally, the 64-bit net address replaces 64 of th e 384 bits of constant data used in the hash operation. contact maxim for details of the message block organization. the host and the DS2784 both calculat e the result based on the mutually k nown secret. the result of the hash operation is known as the message authentication code (m ac) or message digest. the mac is returned by the DS2784 for comparison to the host?s mac. note that the se cret is never transmitted on the bus and thus cannot be captured by observing bus traffic. each authentication attempt is initiated by the host sy stem by providing a 64-bit random challenge by the write challenge command. the hos t then issues the compute mac or compute mac with rom id command. the mac is computed per fips 180, and th en returned as a 160-bit serial stream, beginning with the least significant bit. DS2784 authentica tion commands write challenge [0ch]. this command writes the 64-bit challenge to the DS2784. the lsb of the 64-bit data argument can begin immediately after the msb of the command has been completed. if more than 64-bits are written, the final value in the challenge register w ill be indeterminate. the write challenge command must be issued prior to every compute mac or comput e next secret command for reliable results. compute mac without rom id [36h]. this command initiates a sha-1 computation without including the rom id in the message block. since the rom id is not us ed, this command allows the use of a master secret and mac response independent of the rom id. the DS2784 computes the mac in t sha after receiving the last bit of this command. after the mac computation is complete, the host must write 8 write-zero time slots and then issue 160 read-time slots to receive the 20-byte mac. see figure 9 for command timing. compute mac with rom id [35h] this command is structured the same as the compute mac without rom id, except that the rom id is included in the message block. with the rom id unique to each ds27 84 included in the mac comput ation, the mac is unique to each token. see white paper 4: glossary of 1-wire sha-1 terms , for more information. see figure 9 for command timing. sha-1-related commands used while authenticating a battery or peripheral device are summarized in table 9 for convenience. four additional commands for clearing, computi ng, and locking of the secret are described in detail in the following section. table 9. authentication function commands command hex function write challenge 0c writes 64-bit challenge for sha-1 processing. required prior to issuing compute mac and compute next secret commands. compute mac without rom id and return mac 36 computes hash operation of the message block with logical 1s in place of the rom id. returns the 160-bit mac. compute mac with rom id and return mac 35 computes hash operation of t he message block including the rom id. returns the 160-bit mac.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 30 of 38 secret management function commands clear secret [5ah] . this command sets the 64-bit secret to all 0s (0000 0000 0000 0000h). the host must wait t eec for the DS2784 to write the new secret value to eeprom. s ee figure 12 for command timing. compute next secret without rom id [30h]. this command initiates a sha-1 computation of the mac and uses a portion of the resulting mac as the next or new secret. the hash operation is performed with the current 64-bit secret and the 64-bit challenge. logical 1s are loaded in place of the rom id. 64 bits of the output mac are used as the new secret value. the host must allow t sha after issuing this command for the sha calculation to complete, then wait t eec for the DS2784 to write the new secr et value to eeprom. see figure 10 for command timing. compute next secret with rom id [33h]. this command initiates a sha-1 computation of the mac and uses a portion of the resulting mac as the next or new se cret. the hash operation is performed with the current 64- bit secret, the 64-bit rom id and the 64-bit challenge. 64 bi ts of the output mac are used as the new secret value. the host must allow t sha after issuing this command for the sha calculation to complete, then wait t eec for the DS2784 to write the new secret value to eeprom. see figure 10 for command timing. lock secret [60h]. this command write protects the 64-bit secret to prevent accidental or malicious overwrite of the secret value. the secret value stored in eeprom becomes ?final?. the host must wait t eec for the DS2784 to write the lock secret bit to eeprom. see figure 12 for command timing. table 10. secret loa ding function commands command hex function clear secret 5a clears the 64-bit secret to 0000 0000 0000 0000h. compute next secret without rom id 30 generates new global secret. compute next secret with rom id 33 generates new unique secret. lock secret 60 sets lock bit to prevent changes to the secret. 1-wire bus system the 1-wire bus is a system that has a single bus master and one or more slaves. a multidrop bus is a 1-wire bus with multiple slaves, while a single-drop bus has only one slave device. in all inst ances, the DS2784 is a slave device. the bus master is typically a mi croprocessor in the host system. the di scussion of this bus system consists of five topics: 64-bit net address, crc generation, hardw are configuration, transact ion sequence, and 1-wire signaling. 64-bit net address (rom id) each DS2784 has a unique, factory-programmed 1-wire net address that is 64 bits in length. the term net address is synonymous with the rom id or rom code terms used in the ds2502 and other 1-wire documentation. the first eight bits of the net address are the 1 -wire family code (32h). the next 48 bits are a unique serial number. the last eight bits are a cyclic redundancy chec k (crc) of the first 56 bits (see figure 6). the 64-bit net address and the 1-wire i/o circuitry built into the device enable the DS2784 to communicate through the 1-wire protocol detailed in this data sheet. figure 6. 1-wire net address format 8-bit crc 48-bit serial number 8-bit family code (32h) msb lsb
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 31 of 38 crc generation the DS2784 has an 8-bit crc stored in the most signifi cant byte of its 1-wire net address and generates a crc during some command protocols. to ensure error-free tr ansmission of the address, t he host system can compute a crc value from the first 56 bits of the addres s and compare it to the crc from the DS2784. the host system is responsible for verifying the crc value and taking action as a result. the DS2784 does not compare crc values and does not prevent a command sequen ce from proceeding as a result of a crc mismatch. proper use of the crc can result in a communicati on channel with a very high level of integrity. the crc can be generated by the host using a circuit cons isting of a shift register and xor gates as shown in figure 7, or it can be generated in software using the polynomial x 8 + x 5 + x 4 + 1. additional information about the dallas 1-wire crc is available in application note 27: understanding and using cyclic redundancy checks with dallas semiconductor i button products . in the circuit in figure 7, the shift register bits are initia lized to 0. then, starting with the least significant bit of the family code, one bit at a time is shifted in. after the 8th bit of the family code has been entered, then the serial number is entered. after the 48th bit of the serial num ber has been entered, the shift register contains the crc value. figure 7. 1-wire crc generation block diagram during some command sequences, the DS2784 also generates an 8-bit crc and provides this value to the bus master to facilitate validation for the transfer of command, address, and data from the bus master to the DS2784. the DS2784 computes an 8-bit crc for the command and address bytes received from the bus master for the read memory, read status, and read/generate crc command s to confirm that these bytes have been received correctly. the crc generator on the DS2784 is also used to provide verification of error-free data transfer as each eeprom page is sent to the mast er during a read data/generate cr c command and for the 8 bytes of information in the status memory field. in each case where a crc is used for data transfer vali dation, the bus master must calculate the crc value using the same polynomial function and compare the calculated value to the crc either stored in the DS2784 net address or computed by the DS2784. the comparison of crc values and decision to continue with an operation are determined entirely by the bus master. there is no circuitry in the DS2784 that prevents the command sequence from proceeding if the stored or calculated crc from the DS2784 and the ca lculated crc from the host do not match. hardware configuration because the 1-wire bus has only a single line, it is importa nt that each device on the bus be able to drive it at the appropriate time. to facilitate this, each device attached to the 1-wire bus must connect to the bus with open-drain or tri-state output driver s. the DS2784 uses an open-drai n output driver as part of the bidirectional interface circuitry shown in figure 8. if a bidirectional pin is not available on the bus master, separate output, and input pins can be connected together. msb xor xor lsb xor input
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 32 of 38 the 1-wire bus must have a pullup resistor at t he bus-master end of the bus. a value of between 2k and 5k is recommended. the idle state for the 1-wire bus is high. if, for any reason, a bus tran saction must be suspended, the bus must be left in the idle state to properly resume the transaction later. note that if the bus is left low for more than t low0 , slave devices on the bus begin to interpret the low period as a reset pulse, effectively terminating the transaction. figure 8. 1-wire bu s interface circuitry transaction sequence the protocol for accessing the DS2784 th rough the 1-wire port is as follows: ? initialization ? net address command ? function command(s) ? data transfer (not all commands have data transfer) all transactions of the 1-wire bus begin with an initializati on sequence consisting of a reset pulse transmitted by the bus master, followed by a presence pulse simultaneously transmitted by the DS2784 and any other slaves on the bus. the presence pulse tells the bus master that one or more devices are on the bus and ready to operate. for more details, see the 1-wire signaling section. net address commands once the bus master has detected the presence of one or more slaves, it can issue one of the net address commands described in the following paragraphs. the name of each net address command (rom command) is followed by the 8-bit op code for that command in square brackets. read net address [33h]. this command allows the bus master to read the DS2784?s 1-wire net address. this command can only be used if there is a single slave on the bus. if more than one slave is present, a data collision occurs when all slaves try to transmit at the same time (open drain produces a wired-and result). match net address [55h]. this command allows the bus master to specifically address one DS2784 on the 1-wire bus. only the addressed DS2784 responds to any subsequent function command. all other slave devices ignore the function command and wait for a reset pulse. this command can be used with one or more slave devices on the bus. skip net address [cch]. this command saves time when there is only one DS2784 on the bus by allowing the bus master to issue a function command without specifyi ng the address of the slave. if more than one slave device is present on the bus, a subsequent function command c an cause a data collision when all slaves transmit data at the same time.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 33 of 38 search net address [f0h]. this command allows the bus master to use a process of elimination to identify the 1-wire net addresses of all slave devic es on the bus. the search process involves the repetition of a simple three- step routine: read a bit, read the complement of the bit, t hen write the desired value of that bit. the bus master performs this simple three-step routine on each bit locati on of the net address. after one complete pass through all 64 bits, the bus master knows the address of one devic e. the remaining devices can then be identified on additional iterations of the pr ocess. see chapter 5 of the book of i button ? standards for a comprehensive discussion of a net address search, including an actual example ( www.maxim-ic.com/ibuttonbook ). function commands after successfully completing one of the net address comma nds, the bus master can ac cess the features of the DS2784 with any of the function commands described in the following paragraphs. the name of each function is followed by the 8-bit op code for that command in square brackets. the function commands are summarized below in table 11. read data [69h, xx]. this command reads data from the DS2784 star ting at memory address xx. the lsb of the data in address xx is available to be read immediately after the msb of the address has been entered. because the address is automatically incremente d after the msb of each byte is rece ived, the lsb of the data at address xx + 1 is available to be read immediately after the msb of the data at address xx. if t he bus master continues to read beyond address ffh, data is r ead starting at memory address 00 and the address is automatically incremented until a reset pulse occurs. addresses labeled ?reserved? in the memory map contain undefined data values. the read data command can be terminated by t he bus master with a reset pulse at any bit boundary. reads from eeprom block addresses retu rn the data in the shadow ram. a recall data command is required to transfer data from the eeprom to the s hadow. see table 7 for more details. write data [6ch, xx]. this command writes data to the DS2784 star ting at memory address xx. the lsb of the data to be stored at address xx can be written immedi ately after the msb of address has been entered. because the address is automatically incremented after the msb of each byte is written, the lsb to be stored at address xx + 1 can be written immediately after the msb to be stor ed at address xx. if the bus master continues to write beyond address ffh, the data starting at address 00 is ov erwritten. writes to read-only addresses, reserved addresses and locked eeprom bl ocks are ignored. incomple te bytes are not written. writes to unlocked eeprom block addresses modify the shadow ram. a copy data command is required to transfer data from the shadow to the eeprom. see table 7 for more details. copy data [48h, xx]. this command copies the contents of the eeprom shadow ram to eeprom cells for the eeprom block containing address xx. copy data commands that address lock ed blocks are ignored. while the copy data command is executing, t he eec bit in the eeprom register is set to 1 and writes to eeprom addresses are ignored. reads and writes to non-eeprom addr esses can still occur while the copy is in progress. the copy data command takes t eec time to execute, starting on the next falling edge after the address is transmitted. recall data [b8h, xx]. this command recalls the cont ents of the eeprom cells to the eeprom shadow memory for the eeprom block containing address xx. lock [6ah, xx]. this command locks (write protects) the block of eeprom containing address xx. the lock bit in the eeprom register must be set to 1 before the lock command is executed. to help prevent unintentional locks, one must issue the lock command immediately after setting the lock bit (eeprom register, address 1fh, bit 06) to a 1. if the lock bit is 0 or if setting the lock bit to 1 does not immediately precede the lock command, the lock command has no effect. the lock command is permanent; a locked block can never be written again. i button is a registered trademark of dallas semiconductor, a wholly owned subsidiary of maxim integrated products, inc.
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 34 of 38 table 11. all function commands command hex description write challenge 0c writes 64-bit challenge for sha-1 processing. required immediately prior to all comput e mac and compute next secret commands. compute mac without rom id and return mac 36 computes hash operation of message block with logical 1s in place of the rom id. compute mac with rom id and return mac 35 computes hash operation of message block using the rom id. clear secret 5a clears the 64-b it secret to 0000 0000 0000 0000h. compute next secret without rom id 30 generates new global secret. compute next secret with rom id 33 generates new unique secret. lock secret 60 sets lock bit to prevent changes to the secret. read data 69, xx reads data from memory starting at address xx. write data 6c, xx writes data to memory starting at address xx. copy data 48, xx copies shadow ram data to eepr om block containing address xx. recall data b8, xx recalls eeprom bl ock containing address xx to ram. lock 6a, xx permanently locks the block of eeprom containing address xx. set overdrive 8b sets 1-wire interface timings to overdrive. clear overdrive 8d sets 1-wire interfac e timings to standard (factory default). reset c4 resets DS2784 (software por).
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 35 of 38 table 12. guide to function command requirements command issue memory address issue 00h before read read/write time slots write challenge ? ? write: 64 compute mac ? yes read: up to 160 compute next secret ? ? ? clear/lock secret, set/clear overdrive ? ? ? read data 8 bits ? read: up to 2048 write data 8 bits ? write: up to 2048 copy data 8 bits ? ? recall data 8 bits ? ? lock 8 bits ? ? reset ? ? ? figure 9. compute mac function command 8 write 0 time slots up to 160 read time slots (read 20-byte mac) skip rom cmd compute mac cmd 1-wire reset presence pulse t sha wait for mac computation
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 36 of 38 figure 10. compute next secret function command figure 11. copy function command skip rom cmd copy cmd 1-wire reset presence pulse wait for eeprom programming t eec 8 write time slots figure 12. clear/lock secret, set/ clear overdrive function commands
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 37 of 38 i/o signaling the 1-wire bus requires strict signaling protocols to ens ure data integrity. the four protocols used by the DS2784 are as follows: the initialization sequence (reset pulse follo wed by presence pulse), write 0, write 1, and read data. the bus master initiates all these type s of signaling except the presence pulse. the initialization sequence required to begin any comm unication with the DS2784 is shown in figure 13. a presence pulse following a reset pulse indicates that t he DS2784 is ready to accept a net address command. the bus master transmits (tx) a reset pulse for t rstl . the bus master then releases the line and goes into receive mode (rx). the 1-wire bus line is then pulled high by the pu llup resistor. after detecting the rising edge on the dq pin, the DS2784 waits for t pdh and then transmits the presence pulse for t pdl . figure 13. 1-wire in itialization sequence write-time slots a write-time slot is initiated when the bus master pulls the 1-wire bus from a l ogic-high (inactive) level to a logic-low level. there are two types of writ e-time slots: write 1 and write 0. all write-time slots must be t slot in duration with a 1 s minimum recovery time, t rec , between cycles. the DS2784 sample s the 1-wire bus line between t low1_max and t low0_min after the line falls. if the line is high when sampled, a write 1 occurs. if the line is low when sampled, a write 0 occurs. the sample window is illustrated in figure 14. for the bus master to generate a write-1 time slot, the bus line must be pulled low and then released, allowing the line to be pulled high less than t rdv after the start of the write time slot. for the host to generate a write 0 time slot, the bus line must be pulled low and held low for the duration of the write-time slot. read-time slots a read-time slot is initiated when the bus master pulls the 1-wire bus line from a logic-high level to a logic-low level. the bus master must keep the bus line low for at least 1 s and then release it to allow the DS2784 to present valid data. the bus master can then sample the data t rdv from the start of the read-time slot. by the end of the read-time slot, the DS2784 releases the bus line and allows it to be pu lled high by the external pullup resistor. all read-time slots must be t slot in duration with a 1 s minimum recovery time, t rec , between cycles. see figure 14 and the timing specifications in the electrical characteristics table for more information. t r s tl t pdl t r s th t pdh pack+ pack- line type legend: bus master active low DS2784 active low resistor pullup both bus master and DS2784 active low dq
DS2784: 1-cell stand-alone fuel gauge ic with li+ protector and sha-1 authentication 38 of 38 figure 14. 1-wire writ e and read-time slots package information for the latest package outline information, go to www.maxim-ic.com/dallaspackinfo . maxim cannot assume responsibility for use of any circuitry ot her than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circ uitry and specifications wi thout notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2007 maxim integrated products is a registered trademark of maxim integrated products

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