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DS2786BG+
Stand-Alone OCV-Based Fuel Gauge
General DescriptionThe DS2786B estimates available capacity for recharge-
able Li-ion (Li+) and Li+ polymer batteries based on the
cell voltage in the open-circuit state following a relax-
ation period. The open-circuit voltage (OCV) is used to
determine relative cell capacity based on a lookup table
stored in the IC. This capability makes accurate capacity
information available immediately after a battery pack is
inserted. During periods of moderate to high rate dis-
charging, which preclude OCV measurements, the
DS2786B uses coulomb counting as a secondary
means of estimating relative capacity.
Remaining capacity is reported in percent, along with
cell voltage, current, and temperature information. Cell
characteristics and application parameters used in the
calculations are stored in on-chip EEPROM.
The DS2786B is intended for use on the host side of
portable devices, though it can also be mounted within a
battery pack. Measurement and estimated capacity data
are accessed through an I2C interface. Temperature
data is available from an on-die sensor. Resistance mea-
surements of a pack identification resistor and pack ther-
mistor are supported by ratiometric measurements on
two auxiliary inputs.
The DS2786B comes in a 10-pin, lead-free, TDFN 3mm
x 3mm package with an exposed pad (EP).
Applications3G Multimedia Wireless Handsets
Digital Still Cameras
Digital Audio (MP3) Players
FeaturesRelative Capacity Calculated from Combination
Coulomb Counter and Open-Circuit Cell Voltage
(OCV) Battery ModelAccurate Warning of Low-Battery Conditions
Even on First Cycle (No Learn Cycle Needed)12-Bit Battery Voltage Measurement
±10mV Accuracy
1.22mV LSB, 0V to 4.5V Input Range11-Bit Bidirectional Current Measurement
25µV LSB, ±51.2mV Dynamic Range
1.67mA LSB, ±3.4A (RSNS = 15mΩ)Current Accumulation Measurement Resolution
±204.8mVh Range
±13.65Ah (RSNS = 15mΩ)Internal Temperature Measurement
0.125°C LSB, ±3°C AccuracyTwo 11-Bit Auxiliary Input-Voltage Measurements
±8 LSB Accuracy, Ratiometric Inputs Eliminate
Supply Accuracy IssuesVOUTPin Drives Resistive Dividers, Reduces
Current Consumption2-Wire InterfaceLow Power Consumption
Active Current: 50µA (typ), 80µA (max)
Sleep Current: 1µA (typ), 3µA (max)
DS2786B
Stand-Alone OCV-Based Fuel Gauge
Ordering InformationRSNS
AIN0
VOUT
AIN1
SDA
SCL
Li+
PROTECTION
CIRCUIT
THERMISTOR
PACKID
I2C
INTERFACE
SYSTEM
VSSSNS
VIN
(EEPROM PROGRAMMING TEST POINT NOT SHOWN)
DS2786B
Operating Diagram19-5223; Rev 1; 4/10
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
T&R = Tape and reel.
PARTTEMP RANGEPIN-PACKAGE DS2786BG+ -20°C to +70°C 10 TDFN-EP*
DS2786BG+T&R -20°C to +70°C 10 TDFN-EP*
DS2786B
Stand-Alone OCV-Based Fuel Gauge
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS(2.5V ≤VDD≤4.5V, TA= -20°C to +70°C, unless otherwise noted.)
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
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage on All Pins Except VPROGRelative to VSS...-0.3V to +6V
Voltage on VPROGRelative to VSS..........................-0.3V to +18V
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range.............................-55°C to +125°C
Lead Temperature (soldering, 10s).................................+300°C
Soldering Temperature (reflow).......................................+260°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSActive Current IACTIVE 50 75 μA
VDD= 2.0V, SCL, SDA = VSS 0.3 1.0 Sleep-Mode Current ISLEEPSCL, SDA = VSS 1 3 μA
Current-Measurement Resolution ILSB 25 μV
Current-Measurement
Full-Scale Magnitude IFS (Note 1) ±51.2 mV
Current-Measurement
Offset Error IOERR (Note 2) -50 +50 μV
Current-Measurement Gain Error IGERR -1.5 +1.5 % of
reading
VDD= 3.6V at +25°C -1 +1
TA = 0°C to +70°C -2 +2 Timebase Accuracy tERR
TA = -20°C to +70°C -3 +3
VDD= VIN= 3.6V, TA = 0°C to +50°C -10 +10 Voltage Error VGERRTA = -20°C to +70°C -20 +20 mV
Input Resistance VIN, AIN0, AIN1 RIN 15 M
AIN0, AIN1 Error -8 +8 LSB
VOUT Output Drive IO = 1mA VDD -
0.5 V
VOUT Precharge Time tPRE 13.2 13.7 14.2 ms
Temperature Error TERR -3 +3 °C
RECOMMENDED DC OPERATING PROCEDURE(2.5V ≤VDD≤4.5V, TA= -20°C to +70°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSSupply Voltage VDD (Note 1) +2.5 +4.5 V
Data I/O Pins SCL, SDA (Note 1) -0.3 +4.5 V
Programming Pin VPROG (Note 1) -0.3 +15.5 V
VIN, AIN0, AIN1 Pin VIN, AIN0,
AIN1 (Note 1) -0.3 VDD +
0.3 V
DS2786B
Stand-Alone OCV-Based Fuel Gauge
Note 1:All voltages are referenced to VSS.
Note 2:Offset specified after autocalibration cycle and Current Offset Bias Register = 00h.
Note 3:The DS2786B enters the sleep mode 1.5s to 2.2s after (SCL < VIL) and(SDA < VIL).
Note 4:Timing must be fast enough to prevent the DS2786B from entering sleep mode due to bus low for period > tSLEEP.
Note 5:fSCLmust meet the minimum clock low time plus the rise/fall times.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSInput Logic-High: SCL, SDA VIH (Note 1) 1.4 V
Input Logic-Low: SCL, SDA VIL (Note 1) 0.6 V
Output Logic-Low: SDA VOL IOL = 4mA (Note 1) 0.4 V
Pulldown Current: SCL, SDA IPD VDD= 4.2V, VPIN = 0.4V 0.2 1.0 μA
VPROG Pulldown RVPROG 20 k
Input Capacitance: SCL, SDA CBUS 50 pF
Bus Low Timeout tSLEEP (Note 3) 1.5 2.2 s
EEPROM Programming Voltage VPROG 14 15 V
EEPROM Programming Current IPROG 2 mA
EEPROM Programming Time tPROG 3.1 14 ms
EEPROM Copy Endurance 100 Writes
DC ELECTRICAL CHARACTERISTICS (continued)(2.5V ≤VDD≤4.5V, TA= -20°C to +70°C, unless otherwise noted.)
ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE(2.5V ≤VDD≤4.5V, TA= -20°C to +70°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSSCL Clock Frequency fSCL (Note 4) 0 400 kHz
Bus Free Time Between a STOP
and START Condition tBUF 1.3 μs
Hold Time (Repeated)
START Condition tHD:STA(Note 5) 0.6 μs
Low Period of SCL Clock tLOW 1.3 μs
High Period of SCL Clock tHIGH 0.6 μs
Setup Time for a Repeated
START Condition tSU:STA 0.6 μs
Data Hold Time tHD:DAT (Notes 6, 7) 0 0.9 μs
Data Setup Time tSU:DAT (Note 6) 100 ns
Rise Time of Both SDA and
SCL Signals tR20 +
0.1CB 300 ns
Fall Time of Both SDA and
SCL Signals tF20 +
0.1CB 300 ns
Setup Time for STOP Condition tSU:STO 0.6 μs
Spike Pulse Widths Suppressed
by Input Filter tSP(Note 8) 0 50 ns
Capacitive Load for Each Bus Line CB(Note 9) 400 pF
SCL, SDA Input Capacitance CBIN 60 pF
DS2786B
Stand-Alone OCV-Based Fuel Gauge
Note 6:The maximum tHD:DAT has only to be met if the device does not stretch the low period (tLOW) of the SCL signal.
Note 7:This device internally provides a hold time of at least 100ns for the SDA signal (referred to the VIHMINof the SCL signal) to
bridge the undefined region of the falling edge of SCL.
Note 8:Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant.
Note 9:CB—total capacitance of one bus line in pF.
ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (continued)(2.5V ≤VDD≤4.5V, TA= -20°C to +70°C.)
SDA
SCL
tLOW
tHD:STA
tHD:DAT
tSU:STAtSU:STO
tSU:DAT
tHD:STA
tSPtRtBUF
SSrPS
Figure 1. 2-Wire Bus Timing Diagram
DS2786B
Stand-Alone OCV-Based Fuel Gauge
Pin Description
PINNAMEFUNCTIONAIN1 Auxiliary Voltage Input Number 1AIN0 Auxiliary Voltage Input Number 0
3 SCL Serial Clock Input. Input only 2-wire clock line. Connect this pin to the clock signal of the 2-wire
interface. This pin has a 0.2μA typical pulldown to sense disconnection.
4 SDA Serial Data Input/Output. Open-drain 2-wire data line. Connect this pin to the clock signal of the 2-
wire interface. This pin has a 0.2μA typical pulldown to sense disconnection. SNS Current-Sense Input. Connect to the handset side of the sense resistor.
6 VSS Device Ground. Connect to the battery side of the sense resistor.
7 VPROGEEPROM Programming Voltage Input. Connect to external supply for production programming.
Connect to VSS during normal operation.
8 VOUTVoltage Out. Supply for auxiliary input voltage measurement dividers. Connect to high side of
resistor-divider circuits.
9 VIN Battery Voltage Input. The voltage of the cell pack is measured through this pin.
10 VDDPower-Supply Input. 2.5V to 4.5V Input Range. Connect to system power through a decoupling
network. EP Exposed Pad. Connect to VSS.
VDD
VOUT
VPROG
AIN1
SCL
SDAVINAIN0VSSSNS
TDFN
(3mm x 3mm)TOP VIEW
DS2786B
Pin Configuration
DS2786B
Stand-Alone OCV-Based Fuel Gauge2-WIRE
INTERFACE
ADC
SDA
SCL
GROUND
VDD
VSS
BIAS
1kΩ
1kΩ
VINAIN0
AIN1
SNS
VOUT
SWITCH IS ON WHEN AIN0 OR AIN1 IS BEING MEASURED.
VOLTAGE
REFERENCE
STATE
MACHINE
EEPROMVPROG
TIMEBASE
TEMPERATURE
MEASUREMENT
Figure 2. Block Diagram
Detailed DescriptionThe DS2786B provides current-flow, voltage, and
temperature-measurement data to support battery-
capacity monitoring in cost-sensitive applications.
Current is measured bidirectionally over a dynamic
range of ±51.2mV with a resolution of 25µV. Assuming
a 15mΩsense resistor, the current-sense range is
±3.4A, with a 1 least significant bit (LSB) resolution of
1.667mA. Current measurements are performed at reg-
ular intervals and each measurement is accumulated
internally to coulomb count host power consumption.
Each current measurement is reported with sign and
magnitude in the 2-byte Current Register. Battery-
voltage measurements are reported in the 2-byte
Voltage Register with 12-bit (1.22mV) resolution, and
auxiliary voltage measurements are reported in the 2-
byte Aux Volt Registers with 11-bit resolution.
Additionally, the Temperature Register reports tempera-
ture with 0.125°C resolution and ±3°C accuracy from
the on-chip sensor. The on-chip temperature measure-
ment is optional and replaces auxiliary voltage channel
AIN1. Figure 1 is the 2-wire bus timing diagram; Figure
2 is the DS2786B block diagram. Figure 3 is an appli-
cation example.
DS2786B
Stand-Alone OCV-Based Fuel GaugeThe DS2786B provides accurate relative capacity mea-
surements during periods of host system inactivity by
looking at cell open-circuit voltage. Cell capacity is cal-
culated using an OCV voltage profile and a 1-byte
scale factor to weight-accumulated current. The OCV
voltage profile and scale factor are stored in EEPROM
memory. The EEPROM memory is constructed with a
SRAM shadow so that the OCV voltage profile and
scale factor can be overwritten by the host to accom-
modate a variety of cell types and capacities from mul-
tiple-cell vendors. The I2C interface also allows
read/write access to the Status, Configuration, and
Measurement Registers.
Power ModesThe DS2786B operates in one of two power modes:
Active and Sleep. While in Active Mode, the DS2786B
operates as a high-precision battery monitor with temper-
ature, voltage, auxiliary inputs, current, and accumulated
current measurements acquired continuously and the
resulting values updated in the measurement registers. In
Sleep Mode, the DS2786B operates in a low-power mode
with no measurement activity. Read-and-write access is
allowed to all registers in either mode.
The DS2786B operating mode transitions from sleep to
active when:
(SCL > VIH) or(SDA > VIH)
The DS2786B operating mode transitions from Active to
Sleep when:
SMOD = 1 and(SCL < VIL) and(SDA < VIL)
for tSLEEP
Caution: If SMOD = 1, a pullup resistor is required onSCL and SDA in order to ensure that the DS2786B tran-
sitions from Sleep to Active Mode when the battery is
charged. If the bus is not pulled up, the DS2786B
remains in Sleep and cannot accumulate the charge
current. This caution statement applies particularly to a
battery that is charged on a standalone charger.
AIN0
VINVOUT
AIN1SDA
VSS
SCL
(1) OPTIONAL FOR 8kV/15kV ESD
SNS
VDD VPROG
PACK-
PACK+
PACKID
THERM
PROTECTION IC
(Li+/POLYMER)
SYSTEM
VSS
SYSTEM
SERIAL
BUS
PROGRAMMING
TEST POINT
SYSTEM
VDD
BATTERYSYSTEM
RSNS
150Ω
10nF
5.6V(1)
1kΩ
1nF1nF
1kΩ
1kΩ
2.5V(1)
DS2786B
Figure 3. Application Example
DS2786B
Stand-Alone OCV-Based Fuel GaugeINACTIVEINACTIVE
ACTIVE
(INACTIVE FOR TEMPERATURE MEASUREMENT)
VIN PIN
MEASUREMENTAVERAGE OVER 440ms
NEW REGISTER VALUE
NEW REGISTER VALUE
NEW REGISTER VALUE
0.86ms
DELAY
0.86ms
DELAY
0.86ms
DELAY
0.86ms
DELAY
tPRE
VOLTAGE
REGISTER
VOUT PIN
ALTERNATING AIN0 OR
AIN1/TEMPERATURE
MEASUREMENT
AIN0 OR AIN1/
TEMPERATURE REGISTER
DIFFERENTIAL
CURRENT
MEASUREMENT
CURRENT
REGISTER
CYCLE OF MEASUREMENTS REPEATS EVERY 880ms.
AVERAGE OVER 220ms
AVERAGE OVER 220ms
440ms220ms220ms
Figure 4. Measurement Sequence
Parameter MeasurementThe DS2786B uses a sigma-delta A/D converter to
make measurements. The measurement sequence
shown in Figure 4 repeats continuously while the
DS2786B is in Active Mode. The VOUTpin is activated
tPREbefore the AIN0 and AIN1 conversion to allow for
the VOUToutput voltage to settle. The DS2786B can be
configured to measure temperature using its on-chip
sensor instead of the AIN1 input. When the internal tem-
perature measurement uses the AIN1 conversion time-
slot, VOUTis not activated. A full sequence of voltage
measurements nominally takes 1760ms to complete.
DS2786B
Stand-Alone OCV-Based Fuel Gauge
Voltage MeasurementBattery voltage is measured at the VINinput with respect
to VSSover a 0 to 4.999V range and with a resolution of
1.22mV. The result is updated every 880ms and placed
in the Voltage Register in two’s-complement form.
Voltages above the maximum register value are reported
as 7FFFh. Figure 5 is the Voltage Register format.
The input impedance of VINis sufficiently large
(> 15MΩ) to be connected to a high-impedance volt-
age-divider in order to support multiple-cell applica-
tions. The pack voltage should be divided by the
number of series cells to present a single-cell average
voltage to the VINinput.
Every 1024th conversion, the ADC measures its input
offset to facilitate offset correction to improve voltage
accuracy. Offset correction occurs approximately every
15min. The resulting correction factor is applied to the
subsequent 1023 measurements. During the offset-cor-
rection conversion, the ADC does not measure the VIN
signal. The voltage measurement just prior to the offset
conversion is displayed in the Voltage Register. The
OCV algorithm automatically adjusts for the effects of
the offset-correction cycle.
Auxilary Input MeasurementsThe DS2786B has two auxiliary voltage-measurement
inputs, AIN0 and AIN1. Both are measured with respect
to VSS. These inputs are designed for measuring resis-
tor ratios, particularly useful for measuring thermistor or
pack identification resistors. Prior to the beginning of a
measurement cycle on AIN0 or AIN1, the VOUTpin out-
puts a reference voltage in order to drive a resistive
divider formed by a known resistor value, and the
unknown resistance to be measured. This technique
delivers good accuracy at a reasonable cost, as it
removes reference tolerance from the error calcula-
tions. Measurements alternate between each input.
Each auxiliary measurement is therefore updated every
1760ms and placed in the corresponding AIN0 or AIN1
Register in two’s-complement form. Figure 6 shows the
Auxiliary Input Registers format.
MSB—ADDRESS 0Ch LSB—ADDRESS 0Dh
S 211 210 29 28 27 26 25 24 23 22 21 20 X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: 1.22mV
Figure 5. Voltage Register Format
AIN0 MSB—ADDRESS 08h LSB—ADDRESS 09h
S 210 29 28 27 26 25 24 23 22 21 20 X X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: VOUT × 1/2047
AIN1 MSB—ADDRESS 0Ah LSB—ADDRESS 0Bh
S 210 29 28 27 26 25 24 23 22 21 20 X X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: VOUT × 1/2047
Figure 6. Auxiliary Input Registers Format
DS2786B
Stand-Alone OCV-Based Fuel GaugeMSB—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, “X”: RESERVED UNITS: 0.125°C
Figure 7. Temperature Register Format
MSB—ADDRESS 0Eh LSB—ADDRESS 0Fh
S 210 29 28 27 26 25 24 23 22 21 20 X X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: 25μV/RSNS
Figure 8. Current Register Formats
CURRENT RESOLUTION (1 LSB) RSNS|VSS - VSNS|20m15m 10m5m
25μV 1.25mA 1.667mA 2.5mA 5mA
CURRENT INPUT RANGE RSNSVSS- VSNS20m 15m 10m 5m
±51.2mV ±2.56A ±3.41A ±5.12A ±10.24A
Table 1. Current Range and Resolution for Various RSNSValuesemperature MeasurementThe DS2786B uses an integrated temperature sensor to
measure battery temperature with a resolution of
0.125°C. Temperature measurements are updated
every 1760ms and placed in the Temperature Register
in two’s-complement form. The format of the
Temperature Register is shown in Figure 7. The ITEMP
bit in the Status/Configuration Register must be set to
enable the internal temperature measurement instead
of the AIN1 measurement.
Current MeasurementIn the Active Mode of operation, the DS2786B continu-
ally measures the current flow into and out of the bat-
tery by measuring the voltage drop across a low-value
current-sense resistor, RSNS, connected between the
SNS and VSSpins. The voltage-sense range between
SNS and VSSis ±51.2mV. Note that positive current val-
ues occur when VSNSis less than VSS, and negative
current values occur when VSNSis greater than VSS.
Peak signal amplitudes up to 102mV are allowed at the
input as long as the continuous or average signal level
does not exceed ±51.2mV over the conversion-cycle
period. The ADC samples the input differentially and
updates the Current Register every 880ms at the com-
pletion of each conversion cycle. Figure 8 describes
the Current Measurement Register format and resolu-
tion for each option. Charge currents above the maxi-
mum register value are reported at the maximum value
(7FFFh = +51.2mV). Discharge currents below the mini-
mum register value are reported at the minimum value
(8000h = -51.2mV).
Every 1024th conversion, the ADC measures its input
offset to facilitate offset correction to improve current
accuracy. Offset correction occurs approximately every
15min. The resulting correction factor is applied to the
subsequent 1023 measurements. During the offset cor-
rection conversion, the ADC does not make a measure-
ment. The current measurement just prior to the offset
conversion is displayed in the Current Register. See
Table 1 for current range and resolution for various
RSNSvalues.
DS2786B
Stand-Alone OCV-Based Fuel Gauge
Current Offset BiasThe Current Offset Bias Register (COBR) allows a pro-
grammable offset value to be added to raw current
measurements. The result of the raw current measure-
ment plus the COBR value is displayed as the current
measurement result in the Current Register, and is used
for current accumulation and detection of an OCV con-
dition. The COBR value can be used to correct for a sta-
tic offset error, or can be used to intentionally skew the
current results and therefore the current accumulation.
Read and write access is allowed to COBR. Whenever
the COBR is written, the new value is applied to all sub-
sequent current measurements. COBR can be pro-
grammed in 25µV steps to any value between
+3.175mV and -3.2mV. The COBR value is stored as a
two’s-complement value in nonvolatile (NV) memory.
The COBR factory default value is 00h. Figure 9 shows
the Current Offset Bias Register format.
Current AccumulationAn Internal Accumulated Current Register (IACR)
serves as an up/down counter holding a running count
of charge since the last OCV condition. Current mea-
surement results, plus a programmable bias value are
internally summed, or accumulated, at the completion
of each current measurement-conversion period. The
IACR has a range of ±204.8mVh. The IACR uses the
Initial or Learned Cell Capacity Registers to increment
or decrement the Relative Capacity Register as current
flows into or out of the battery. In this way, the fuel
gauge is accurate even when an OCV condition does
not occur for an extended time period. See Table 2 for
the accumulated current range for various RSNSvalues.
Cell-Capacity EstimationThe DS2786B uses a hybrid OCV measurement and
coulomb-counting algorithm to estimate remaining cell
capacity. During periods of charging or discharging the
cell, the DS2786B counts charge flow into and out of
the cell. When the application becomes inactive, the
DS2786B waits for the cell voltage to relax and then
adjusts the coulomb count based on an open-circuit
voltage cell model stored in device EEPROM. The
resulting calculation is reported to the system as a per-
centage value between 0 and 100%. As the cell ages, a
learn feature adjusts for changes in capacity.
The Relative Capacity Register reports remaining cell
charge as a percentage of full. Relative capacity is
reported with a resolution of 0.5% and is limited to a
value between 0% and 100%. The Relative Capacity
Register is updated each time the IC performs a current
measurement or open-circuit cell-voltage measurement.
See Figure 10.
ADDRESS 60h
S 26 25 24 23 22 21 20
MSB LSB
“S”: SIGN BIT UNITS: 25μV/RSNS
Figure 9. Current Offset Bias Register Format
IACR RANGE RSNSVSS- VSNS20m 15m 10m 5m
±204.8mVh ±10.24Ah ±13.65Ah ±20.48Ah ±40.96Ah
Table 2. Accumulated Current Range for
Various RSNSValuesADDRESS 02h 7 26 25 24 23 22 21 20
MSB LSB
UNITS: 0.5%
Figure 10. Relative Capacity Register Format
