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DS2782G+
Stand-Alone Fuel Gauge IC
19-4635; 5/09
DS2782
Stand-Alone Fuel Gauge IC
GENERAL DESCRIPTION The DS2782 measures voltage, temperature and
current, and estimates available capacity for
rechargeable lithium ion and lithium-ion polymer
batteries. Cell characteristics and application
parameters used in the calculations are stored in on-
chip EEPROM. The available capacity registers
report a conservative estimate of the amount of
charge that can be removed given the current
temperature, discharge rate, stored charge and
application parameters. Capacity estimation reported
in mAh remaining and percentage of full.
APPLICATIONS Digital Still Cameras
Sub-Notebook Computers
Handheld PC Data Terminals
3G Multimedia Wireless Handsets
TYPICAL OPERATING CIRCUIT
PIN CONFIGURATIONS
FEATURES Precision Voltage, Temperature, and Current
Measurement System Accurate Stable Internal Time Base Absolute and Relative Capacity Estimated from
Coulomb Count, Discharge Rate, Temperature
and Battery Cell Characteristics Accurate Warning of Low Battery Conditions Automatic Backup of Coulomb Count and Age
Estimation to Nonvolatile (NV) EEPROM Gain and Tempco Calibration Allows the Use of
Low-Cost Sense Resistors 24-Byte User EEPROM or 16-Byte User
EEPROM and Unique 64-Bit ID Industry 2-Wire Interface with Programmable
Slave Address Tiny 8-Pin TSSOP and 10-TDFN Packages
Embed Easily in Thin Prismatic Cell Packs
ORDERING INFORMATION
PART PIN-PACKAGE TOP MARK DS2782E+ 8 TSSOP 2782+
DS2782E+T&R 8 TSSOP 2782+
DS2782G+ 10 TDFN-EP* 2782+
DS2782G+T&R 10 TDFN-EP* 2782+
Note: To order devices with the unique 64-bit ID option, contact Maxim sales. +Denotes a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
*EP = Exposed pad.
DS2782
ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to VSS -0.3V to +6.0V
Voltage Range on VIN Relative to VSS -0.3V to (VDD + 0.3V)
Operating Temperature Range -40°C to +85°C
Storage Temperature Range -55°C to +125°C
Soldering Temperature Refer to the IPC/JEDEC J-STD-020 Specification.
Stresses beyond those listed under “Absolute 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 the absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED DC OPERATING CHARACTERISTICS (VDD = 2.5V to 4.5V; TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply Voltage VDD (Note 1) +2.5 +4.5 V
SCL, VIN Voltage Range (Note 1) -0.3 +4.5 V
SDA, PIO Voltage Range (Note 1) -0.3 +5.5 V
DC ELECTRICAL CHARACTERISTICS (VDD = 2.5V to 4.5V; TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 2.5V ≤ VDD ≤ 4.2V 65 95 ACTIVE Current IACTIVE 105 A
SLEEP Mode Current ISLEEP 2.5V ≤ VDD ≤ 4.2V 1 3 A
Input Logic-High:
SDA, SCL, PIO VIH (Note 1) 1.5 V
Input Logic-Low:
SDA, SCL, PIO VIL (Note 1) 0.6 V
Output Logic-Low:
SDA, PIO VOL IOL = 4mA (Note 1) 0.4 V
Pulldown Current:
SDA, SCL, PIO IPD VSDA, VSCL, VPIO =
0.4V 0.2 A
VIN Input Resistance RIN 15 M
Bus Low to Sleep Time tSLEEP SDA, SCL < VIL
(Note 2) 2.2 s
Undervoltage SLEEP
Threshold VSLEEP (Note 1) 2.40 2.45 2.50 V
ELECTRICAL CHARACTERISTICS: TEMPERATURE, VOLTAGE, CURRENT (VCC = 2.5V to 4.5V; TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Temperature Resolution TLSB 0.125 °C
Temperature Error TERR ±3 °C
Voltage Resolution VLSB 4.88 mV
Voltage Full-Scale VFS 0 4.5 V
Voltage Error VERR ±50 mV
DS2782
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Current Gain Error IGERR (Note 3) ±1 % Full-
Scale
Current Offset Error IOERR
0°C ≤ TA ≤ +70°C,
2.5V ≤ VDD ≤ 4.2V
(Note 5)
-7.82 +12.5 V
Accumulated Current Offset qOERR
0°C ≤ TA ≤ +70°C,
2.5V ≤ VDD ≤ 4.2V
VSNS = VSS
(Notes 4, 5)
-188 +0 Vhr/
day
VDD = 3.8V,
TA = +25°C ±1
0°C ≤ TA ≤ +70°C,
2.5V ≤ VDD ≤ 4.2V ±2 Time-Base Error tERR ±3
ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (2.5V VDD 4.5V, TA = -20C to +70C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS SCL Clock Frequency fSCL (Note 6) 0 400 kHz
Bus Free Time Between a
STOP and START Condition tBUF 1.3 s
Hold Time (Repeated)
START Condition tHD:STA (Note 7) 0.6 s
Low Period of SCL Clock tLOW 1.3 s
High Period of SCL Clock tHIGH 0.6 s
Setup Time for a Repeated
START Condition tSU:STA 0.6 s
Data Hold Time tHD:DAT (Note 8, 9) 0 0.9 s
Data Setup Time tSU:DAT (Note 8) 100 ns
Rise Time of Both SDA and
SCL Signals tR 20 +
0.1CB 300 ns
Fall Time of Both SDA and
SCL Signals tF 20 +
0.1CB 300 ns
Setup Time for STOP
Condition tSU:STO 0.6 s
Spike Pulse Widths
Suppressed by Input Filter tSP (Note 10) 0 50 ns
Capacitive Load for Each Bus
Line CB (Note 11) 400 pF
SCL, SDA Input Capacitance CBIN 60 pF
EEPROM RELIABILITY SPECIFICATION (VCC = 2.5V to 4.5V; TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS EEPROM Copy Time tEEC 10 ms
DS2782
Note 1: All voltages are referenced to VSS.
Note 2: To properly enter sleep mode the application should hold the bus low for longer than the maximum tSLEEP.
Note 3: Factory calibrated accuracy. Higher accuracy can be achieved by in-system calibration by the user.
Note 4: Accumulation bias register set to 00h.
Note 5: Parameters guaranteed by design.
Note 6: Timing must be fast enough to prevent the DS2782 from entering sleep mode due to bus low for period > tSLEEP.
Note 7: fSCL must meet the minimum clock low time plus the rise/fall times.
Note 8: The maximum tHD:DAT has only to be met if the device does not stretch the LOW period (tLOW) of the SCL signal.
Note 9: This device internally provides a hold time of at least 300 ns for the SDA signal (referred to the VIHmin of the SCL signal) to bridge the undefined region of the falling edge of SCL.
Note 10: Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant.
Note 11: CB – total capacitance of one bus line in pF.
Figure 1. I2C Bus Timing Diagram DS2782
PIN DESCRIPTION
PIN
TSSOP TDFN-EP NAME FUNCTION 1 1 N.C.
Not Connected. Pin not connected internally, float or connect to VSS. 2 2, 3 VSS
Device Ground. Connect directly to the negative terminal of the battery cell. Connect the sense resistor between VSS and SNS.
3 4 VIN
Voltage Sense Input. The voltage of the battery cell is monitored through this input pin.
4 5 VDD
Power-Supply Input. Connect to the positive terminal of the battery cell through a decoupling network.
5 6 SDA
Serial Data Input/Output. 2-Wire data line. Open-drain output driver. Connect this pin to the DATA terminal of the battery pack. Pin has an
internal pull-down (IPD) for sensing disconnection.
6 7 SCL
Serial Clock Input. 2-Wire clock line. Input only. Connect this pin to the CLOCK terminal of the battery pack. Pin has an internal pull-down (IPD) for
sensing disconnection.
— 8 N.C.
No Connection 7 9 SNS
Sense Resistor Connection. Connect to the negative terminal of the battery pack. Connect the sense resistor between VSS and SNS.
8 10 PIO
Programmable I/O Pin. Can be configured as input or output to monitor or control user-defined external circuitry. Output driver is open drain. This pin
has a weak internal pulldown (IPD).
— EP EP
Exposed Pad. Connect to VSS or leave floating.
Figure 2. Block Diagram VPOR
SDA
2-Wire
Interface
BIAS/VREFTimebase
Temp
Voltage
ADC
Current ADC
15 bit + sign
Rate,
Temperature
Compensation
EEPROM
Status
Control
Accumulated
Current
SNSVSS
VDD
SCL
PIO
VIN
DS2782
DETAILED DESCRIPTION The DS2782 operates directly from 2.5V to 4.5V and supports single cell Lithium-ion battery packs. As shown in
Figure 3, the DS2782 accommodates multicell applications by adding a voltage regulator for VDD and voltage
divider for VIN. Nonvolatile storage is provided for cell compensation and application parameters. Host side
development of fuel-gauging algorithms is eliminated. On-chip algorithms and convenient status reporting of
operating conditions reduce the serial polling required of the host processor.
Additionally, 16 bytes of EEPROM memory are made available for the exclusive use of the host system and/or
pack manufacturer. The additional EEPROM memory can be used to facilitate battery lot and date tracking and NV
storage of system or battery usage statistics.
Through its 2-Wire interface, the DS2782 gives the host system read/write access to status and control registers,
instrumentation registers, and general-purpose data storage. The 7-bit slave address is field programmable, thus
allowing up to 128 devices to be distinctly addressed by the host system. A unique, factory programmed 64-bit
registration number (8-bit family code + 48-bit serial number + 8-bit CRC) option assures that no two parts are alike
and enables absolute traceability.
Figure 3. Multicell Application Example SDAVDD
SNSVSS
RSNSPack-
Pack+
SDA
Protection
Circuit
PIO
SCL
Multi-Cell
Li-Ion
Battery
0.1uF
VIN
(n-1)
*R
(1)(1)
(1) Components improve IEC1004 Air/Contact ESD compliance
n = number of cells used in the application
R resistors should be selected based on the minimum acceptable resistance (highest acceptable current drain) for the application
4.7uF0.1uF
SCL
DS2782
POWER MODES
The DS2782 has two power modes: ACTIVE and SLEEP. On initial power up, the DS2782 defaults to ACTIVE
mode. While in ACTIVE mode, the DS2782 is fully functional with measurements and capacity estimation
continuously updated. In SLEEP mode, the DS2782 conserves power by disabling measurement and capacity
estimation functions, but preserves register contents. SLEEP mode is entered under two different conditions and
an enable bit for each condition makes entry into SLEEP optional. SLEEP mode can be enabled using the Power
Mode (PMOD) bit or the Under Voltage Enable (UVEN) bit.
The PMOD type SLEEP is entered if the PMOD bit is set AND a bus low condition occurs. A bus low condition,
where both SDA AND SCL low for tSLEEP (2s nominal), is used to detect a pack disconnection or system shutdown
in which the bus pull-up voltage, VPULLUP, is not present. PMOD SLEEP assumes that no charge or discharge
current will flow and therefore coulomb counting is not necessary. A system with PMOD SLEEP enabled must
ensure that a stand-alone or cradle charger includes a pull-up on SDA and/or SCL. The DS2782 transitions from
PMOD SLEEP to ACTIVE mode when either SDA or SCL is pulled high.
The second option for entering SLEEP is an under voltage condition measured on VIN. When the UVEN bit is set,
the DS2782 will transition to SLEEP if the voltage on VIN is less than VSLEEP (2.45V nominal) AND the 2-Wire bus
is in a bus high or a bus low condition for tSLEEP. UVEN SLEEP relieves the battery of the DS2782 load until
communication resumes to prevent over discharging the battery. The DS2782 transitions from UVEN SLEEP to
ACTIVE mode when either SDA or SCL change logic state. The bus master should initiate a transaction after
charging of a depleted battery begins.
Note: PMOD and UVEN SLEEP features must be disabled when a battery is charged on an external charger that
does not connect to SDA and/or SCL. PMOD SLEEP can be used if the charger pulls the bus high. The DS2782
remains in SLEEP and therefore does not measure or accumulate current when a battery is charged on a charger
that fails to properly drive the communication bus.
INITIATING COMMUNICATION IN SLEEP
When beginning communication with a DS2782 in PMOD SLEEP, the bus must be pulled up before a START bit
can be issued by the master. In UVEN SLEEP, the procedure depends on the bus state when UVEN SLEEP was
entered. If the bus was low, it must be pulled up before a START bit can be issued by the master as required with
PMOD SLEEP. If the bus was high when UVEN SLEEP was entered, then the DS2782 is prepared to receive a
START bit from the master. A standard procedure of issuing a START – STOP – START when the host system is
powered up on the charger input properly initiates communication from both PMOD and UVEN SLEEP modes.
VOLTAGE MEASUREMENT
Battery voltage is measured at the VIN input with respect to VSS over a range of 0V to 4.5V, with a resolution of
4.88mV. The result is updated every 440ms and placed in the VOLTAGE register in two’s complement form.
Voltages above the maximum register value are reported at the maximum value; voltages below the minimum
register value are reported at the minimum value. The format of the voltage register is shown in Figure 4.
Figure 4. Voltage Register Format
VOLT Read Only MSB—Address 0Ch LSB—Address 0Dh
S 29 28 27 26 25 24 23 22 21 20 X X X X X
MSb LSb MSb LSb
“S”: sign bit(s), “X”: reserved Units: 4.88mV
DS2782
VIN is usually connected to the positive terminal of a single cell Lithium-Ion battery via a 1k resistor. The input
impedance is sufficiently large (15M) to be connected to a high impedance voltage divider in order to support
multiple cell applications. The pack voltage should be divided by the number of series cells to present a single cell
average voltage to the VIN input. In Figure 3, the value of R can be up to 1M without incurring significant error
due to input loading.
TEMPERATURE MEASUREMENT
The DS2782 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C.
Temperature measurements are updated every 440ms and placed in the temperature register in two’s complement
form. The format of the temperature register is shown in Figure 5.
Figure 5. Temperature Register Format
TEMP Read Only MSB—Address 0Ah LSB—Address 0Bh
S 29 28 27 26 25 24 23 22 21 20 X X X X X
MSb LSb MSb LSb
“S”: sign bit(s), “X”: reserved Units: 0.125C
CURRENT MEASUREMENT
In the ACTIVE mode of operation, the DS2782 continually measures the current flow into and out of the battery by
measuring the voltage drop across a low-value current-sense resistor, RSNS. The voltage-sense range between
SNS and VSS 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 exceed ±51.2mV. The ADC samples
the input differentially at 18.6kHz and updates the Current register at the completion of each conversion cycle.
The Current register is updated every 3.515s with the current conversion result in two’s complement form. Charge
currents above the maximum register value are reported at the maximum value (7FFFh = +51.2mV). Discharge
currents below the minimum register value are reported at the minimum value (8000h = -51.2mV).
Figure 6. Current Register Format
CURRENT Read OnlyMSB—Address 0Eh LSB—Address 0Fh
S 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb
“S”: sign bit(s) Units: 1.5625V/Rsns
CURRENT RESOLUTION (1 LSB)
RSNS VSS -
VSNS 20m 15m 10m 5m
1.5625V 78.13A 104.2A 156.3A 312.5A
DS2782
AVERAGE CURRENT MEASUREMENT
The Average Current register reports an average current level over the preceding 28 seconds. The register value is
updated every 28s in two’s complement form, and is the average of the 8 preceding Current register updates. The
format of the Average Current register is shown in Figure 7. Charge currents above the maximum register value
are reported at the maximum value (7FFFh = +51.2mV). Discharge currents below the minimum register value are
reported at the minimum value (8000h = -51.2mV).
Figure 7. Average Current Register Format
IAVG R/W MSB—Address 08h LSB—Address 09h
S 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb
“S”: sign bit(s) Units: 1.5625V/Rsns
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 factor is applied to the subsequent 1023 measurements.
During the offset correction conversion, the ADC does not measure the sense resistor signal. A maximum error of
1/1024 in the accumulated current register (ACR) is possible; however, to reduce the error, the current
measurement made just prior to the offset conversion is displayed in the current register and is substituted for the
dropped current measurement in the current accumulation process. This results in an accumulated current error
due to offset correction of less than 1/1024.
CURRENT MEASUREMENT CALIBRATION
The DS2782’s current measurement gain can be adjusted through the RSGAIN register, which is factory-calibrated
to meet the data sheet specified accuracy. RSGAIN is user accessible and can be reprogrammed after module or
pack manufacture to improve the current measurement accuracy. Adjusting RSGAIN can correct for variation in an
external sense resistor’s nominal value, and allows the use of low-cost, non-precision current sense resistors.
RSGAIN is an 11-bit value stored in 2 bytes of the Parameter 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, which is reprogrammable, and FRSGAIN, which is read only.
RSGAIN determines the gain used in the current measurement. The read-only FRSGAIN is provided to preserve
the factory value only and is not used in the current measurement.
SENSE RESISTOR TEMPERATURE COMPENSATION
The DS2782 is capable of temperature compensating the current sense resistor to correct for variation in a sense
resistor’s value over temperature. The DS2782 is factory programmed with the sense resistor temperature
coefficient, RSTC, set to zero, which turns off the temperature compensation function. RSTC is user accessible
and can be reprogrammed after module or pack manufacture to improve the current accuracy when using a high
temperature coefficient current-sense resistor. RSTC is an 8-bit value 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 0.5oC boundaries. The
temperature compensation is most effective with the resistor placed as close as possible to the VSS terminal to
optimize thermal coupling of the resistor to the on-chip temperature sensor. If the current shunt is constructed with
DS2782
CURRENT ACCUMULATION
Current measurements are internally summed, or accumulated, at the completion of each conversion period with
the results displayed in the Accumulated Current Register (ACR). The accuracy of the ACR is dependent on both
the current measurement and the conversion time base. The ACR has a range of 0 to 409.6mVh with an LSb of
6.25Vh. Additional read-only registers (ACRL) hold fractional results of each accumulation to avoid truncation
errors. Accumulation of charge current above the maximum register value is reported at the maximum register
value (7FFFh); conversely, accumulation of discharge current below the minimum register value is reported at the
minimum value (8000h).
Charge currents (positive Current register values) less than 100V 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 RSNS = 0.020 and 20mA for RSNS = 0.005.
Read and write access is allowed to the ACR. The ACR must be written MSByte first then LSByte. Whenever the
ACR is written, the fractional accumulation result bits are cleared. The write must be completed within 3.515s (one
ACR register update period). A write to the ACR forces the ADC to perform an offset correction conversion and
update the internal offset correction factor. Current measurement and accumulation begins with the second
conversion following a write to the ACR. Writing ACR clears the fractional values in ACRL. The Format of the ACR
register is shown in Figure 8, and the format of ACRL is shown in Figure 9.
In order to preserve the ACR value in case of power loss, the ACR value is backed up to EEPROM. The ACR
value is recovered from EEPROM on power-up. See the Memory Map in Table 2 for specific address location and
backup frequency.
Figure 8. Accumulated Current Register Format, ACR
ACR R/W & EEMSB—Address 10h LSB—Address 11h 15 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb Units: 6.25Vh/Rsns
DS2782
Figure 9. Fractional/Low Accumulated Current Register Format, ACRL
ACRL Read OnlyMSB—Address 12h LSB—Address 13h 11 210 29 28 27 26 25 24 23 22 21 20 X X X X
MSb LSb MSb LSb
“X”: reserved Units:1.526nVHr/RSNS
ACR LSb
RSNS VSS -
VSNS 20m 15m 10m 5m
6.25Vh 312.5Ah 416.7Ah 625Ah 1.250mAh
ACR RANGE
RSNS VSS -
VSNS 20m 15m 10m 5m
409.6mVh 20.48Ah 27.30Ah 40.96Ah 81.92Ah
ACCUMULATION BIAS
The Accumulation Bias register (AB) allows an arbitrary bias to be introduced into the current-accumulation
process. The AB can be used to account for currents that do not flow through the sense resistor, estimate currents
too small to measure, estimate battery self-discharge or correct for static offset of the individual DS2782 device.
The AB register allows a user programmed constant positive or negative polarity bias to be included in the current
accumulation process. The user-programmed two’s complement value, with bit weighting the same as the current
register, is added to the ACR once per current conversion cycle. The AB value is loaded on power-up from
EEPROM memory. The format of the AB register is shown in Figure 10.
Figure 10. Accumulation Bias Register Formats
AB EE Address 61h
S 26 25 24 23 22 21 20 MSb LSb“S”: sign bit Units: 1.5625V/Rsns
DS2782
CAPACITY ESTIMATION ALGORITHM
Remaining capacity estimation uses real-time measured values and stored parameters describing the cell
characteristics and application operating limits. The following diagram describes the algorithm inputs and outputs.
Figure 11. Top-Level Algorithm Diagram
DS2782
MODELING CELL CHARACTERISTICS
In order to achieve reasonable accuracy in estimating remaining capacity, the cell performance characteristics over
temperature, load current, and charge termination point must be considered. Since the behavior of Li-ion cells is
non-linear, even over a limited temperature range of 10°C to 35°C, these characteristics must be included in the
capacity estimation to achieve a reasonable accuracy. Refer to Application Note AN131: Li+ Fuel Gauging with
Dallas Semiconductor Devices for general information on the FuelPack™ method used in the DS2782. To facilitate
efficient implementation in hardware, a modified version of the method outlined in AN131 is used to store cell
characteristics in the DS2782. Full and empty points are retrieved in a lookup process which re-traces a piece-wise
linear model. Three model curves are stored: Full, Active Empty and Standby Empty. Each model curve is
constructed with 4 line segments and spans from 0°C to 40°C. Operation outside the 0°C to 40°C model span is
supported by the model with minimal loss of accuracy. Above 40°C, the 40°C fixed points are extended with zero
slope. This achieves a conservative capacity estimate for temperatures above 40°C. Below 0°C, the model curves
are extended using the slope of each 0°C to 10°C segment. If low temperature operation is expected, the 0°C to
10°C slopes can be selected to optimize the model accuracy. A diagram of example battery cell model curves is
shown if Figure 12.
Figure 12. Cell Model Example Diagram
Full: The Full curve defines how the full point of a given cell depends on temperature for a given charge
termination. The charge termination method used in the application is used to determine the table values. The
DS2782 reconstructs the Full line from cell characteristic table values 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 temperature variation in the empty point of the discharge profile
based on a high level load current (one that is sustained during a high power operating mode) and the minimum
voltage required for system operation. 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, and the specified minimum
voltage, or Active Empty voltage (VAE) should be a 220ms average to correspond to values read from the Voltage
register. The DS2782 reconstructs the Active Empty line from cell characteristic table values to determine the
Active Empty capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature
increments.
0°C 10°C 20°C 30°C 40°C
100% 3 4
Derivative
[ppm / °C]
Active
Empty
Standby
Empty
FULL Cell
Characterization
data points
DS2782
applications, Standby Empty represents the point that the battery can no longer support RAM refresh and thus the
standby voltage is set by the RAM voltage supply requirements. In other applications, Standby Empty can
represent the point that the battery can no longer support a subset of the full application operation, such as games
or organizer functions on a wireless handset. The standby load current and voltage are used for determining the
cell characteristics but are not programmed into the DS2782. The DS2782 reconstructs the Standby Empty line
from cell characteristic table values to determine the Standby Empty capacity of the battery at each temperature.
Reconstruction occurs in one-degree temperature increments.
CELL MODEL CONSTRUCTION
The model is constructed with all points normalized to the fully charged state at +40°C. Initial values, the +40°C
Full value in mVh units and the +40°C Active Empty value as a fraction of the +40°C Full are stored in the cell
parameter EEPROM block. Standby Empty at +40°C is by definition zero and therefore no storage is required. The
slopes (derivatives) of the 4 segments for each model curve are also stored in the cell parameter EEPROM block.
Segment endpoints are fixed at 0°C, +10°C, +20°C, +30°C and +40°C. An example of data stored in this manner is
shown in Table 1.
Table 1. Example Cell Characterization Table (Normalized to +40°C)
Manufacturers rated cell capacity: 1000mAh
Charge Voltage: 4.2V Charge Current: 500mA Termination Current: 50mA
Active Empty (V, I): 3.0V, 300mA Standby Empty (V, I): 3.0V, 4mA
Sense Resistor: 0.020 +40C
Nominal
[mAh]
0°C +10°C +20°C +30°C +40°C
Full 1051 0.927 0.951 0.974 0.991 1.0
Active Empty 0.051 0.040 0.022 0.012 0.008
Standby Empty 0.013 0.0067 0.0038 0.001 0
Figure 13. Lookup Function Diagram
Cell Model
Parameters
15 bytes
(EEPROM)
Temperature
Lookup
Function
FULL(T)
AE(T)
SE(T)
