General Description
The DS2786B estimates available capacity for recharge-
able Li-ion (Li+) and Li+ polymer batteries based on the
cell voltage in the open-circuit state following a relax-
ation period. The open-circuit voltage (OCV) is used to
determine relative cell capacity based on a lookup table
stored in the IC. This capability makes accurate capacity
information available immediately after a battery pack is
inserted. During periods of moderate to high rate dis-
charging, which preclude OCV measurements, the
DS2786B uses coulomb counting as a secondary
means of estimating relative capacity.
Remaining capacity is reported in percent, along with
cell voltage, current, and temperature information. Cell
characteristics and application parameters used in the
calculations are stored in on-chip EEPROM.
The DS2786B is intended for use on the host side of
portable devices, though it can also be mounted within a
battery pack. Measurement and estimated capacity data
are accessed through an 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).
Applications
3G Multimedia Wireless Handsets
Digital Still Cameras
Digital Audio (MP3) Players
Features
♦Relative Capacity Calculated from Combination
Coulomb Counter and Open-Circuit Cell Voltage
(OCV) Battery Model
♦Accurate Warning of Low-Battery Conditions
Even on First Cycle (No Learn Cycle Needed)
♦12-Bit Battery Voltage Measurement
±10mV Accuracy
1.22mV LSB, 0V to 4.5V Input Range
♦11-Bit Bidirectional Current Measurement
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 Accuracy
♦Two 11-Bit Auxiliary Input-Voltage Measurements
±8 LSB Accuracy, Ratiometric Inputs Eliminate
Supply Accuracy Issues
♦VOUT Pin Drives Resistive Dividers, Reduces
Current Consumption
♦2-Wire Interface
♦Low Power Consumption
Active Current: 50µA (typ), 80µA (max)
Sleep Current: 1µA (typ), 3µA (max)
DS2786B
Stand-Alone OCV-Based Fuel Gauge
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
RSNS
AIN0
VOUT
AIN1
SDA
SCL
Li+
PROTECTION
CIRCUIT
THERMISTOR
PACKID
I2C
INTERFACE
SYSTEM
μP
VSS SNS
VIN
(EEPROM PROGRAMMING TEST POINT NOT SHOWN)
DS2786B
Operating Diagram
19-5223; Rev 1; 4/10
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
*
EP = Exposed pad.
T&R = Tape and reel.
PART TEMP RANGE PIN-PACKAGE
DS2786BG+ -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
2 _______________________________________________________________________________________
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 VPROG Relative to VSS...-0.3V to +6V
Voltage on VPROG Relative 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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Active Current IACTIVE 50 75 μA
VDD = 2.0V, SCL, SDA = VSS 0.3 1.0
Sleep-Mode Current ISLEEP SCL, 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 VGERR TA = -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.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply 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
_______________________________________________________________________________________ 3
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: fSCL must meet the minimum clock low time plus the rise/fall times.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input 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 V
DD = 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.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SCL 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
4 _______________________________________________________________________________________
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 VIHMIN of the SCL signal) to
bridge the undefined region of the falling edge of SCL.
Note 8: Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant.
Note 9: 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
tF
tLOW
tHD:STA
tHD:DAT
tSU:STA tSU:STO
tSU:DAT tHD:STA
tSP tRtBUF
tR
tF
SSr
PS
Figure 1. 2-Wire Bus Timing Diagram
DS2786B
Stand-Alone OCV-Based Fuel Gauge
_______________________________________________________________________________________ 5
Pin Description
PIN NAME FUNCTION
1 AIN1 Auxiliary Voltage Input Number 1
2 AIN0 Auxiliary Voltage Input Number 0
3 SCL
Serial Clock Input. Input only 2-wire clock line. Connect this pin to the 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.
5 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 VPROG EEPROM Programming Voltage Input. Connect to external supply for production programming.
Connect to VSS during normal operation.
8 VOUT Voltage 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 VDD Power-Supply Input. 2.5V to 4.5V Input Range. Connect to system power through a decoupling
network.
— EP Exposed Pad. Connect to VSS.
1
3
4
10
8
7
VDD
VOUT
VPROG
AIN1
EP
SCL
SDA
29
VIN
AIN0
56
VSS
SNS
TDFN
(3mm x 3mm)
TOP VIEW
DS2786B
Pin Configuration
DS2786B
Stand-Alone OCV-Based Fuel Gauge
6 _______________________________________________________________________________________
2-WIRE
INTERFACE
ADC
SDA
SCL
IC
GROUND
VDD
VSS
BIAS
1kΩ
1kΩ
VIN AIN0
AIN1
SNS
VOUT
SWITCH IS ON WHEN AIN0 OR AIN1 IS BEING MEASURED.
VOLTAGE
REFERENCE
STATE
MACHINE
EEPROM VPROG
TIMEBASE
TEMPERATURE
MEASUREMENT
Figure 2. Block Diagram
Detailed Description
The DS2786B provides current-flow, voltage, and
temperature-measurement data to support battery-
capacity monitoring in cost-sensitive applications.
Current is measured bidirectionally over a dynamic
range of ±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 Gauge
_______________________________________________________________________________________ 7
The DS2786B provides accurate relative capacity mea-
surements during periods of host system inactivity by
looking at cell open-circuit voltage. Cell capacity is cal-
culated using an OCV voltage profile and a 1-byte
scale factor to weight-accumulated current. The OCV
voltage profile and scale factor are stored in EEPROM
memory. The EEPROM memory is constructed with a
SRAM shadow so that the OCV voltage profile and
scale factor can be overwritten by the host to accom-
modate a variety of cell types and capacities from mul-
tiple-cell vendors. The I2C interface also allows
read/write access to the Status, Configuration, and
Measurement Registers.
Power Modes
The DS2786B operates in one of two power modes:
Active and Sleep. While in Active Mode, the DS2786B
operates as a high-precision battery monitor with temper-
ature, voltage, auxiliary inputs, current, and accumulated
current measurements acquired continuously and the
resulting values updated in the measurement registers. 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 on
SCL and SDA in order to ensure that the DS2786B tran-
sitions from Sleep to Active Mode when the battery is
charged. If the bus is not pulled up, the DS2786B
remains in Sleep and cannot accumulate the charge
current. This caution statement applies particularly to a
battery that is charged on a standalone charger.
AIN0
VIN
VOUT
AIN1 SDA
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
BATTERY SYSTEM
RSNS
150Ω
10nF
5.6V(1)
1kΩ
1nF 1nF
1kΩ
1kΩ
2.5V (1)
DS2786B
Figure 3. Application Example
DS2786B
Stand-Alone OCV-Based Fuel Gauge
8 _______________________________________________________________________________________
INACTIVE INACTIVE
ACTIVE
(INACTIVE FOR TEMPERATURE MEASUREMENT)
VIN PIN
MEASUREMENT AVERAGE 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
440ms 220ms 220ms
Figure 4. Measurement Sequence
Parameter Measurement
The 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 VOUT pin is activated
tPRE before the AIN0 and AIN1 conversion to allow for
the VOUT output 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, VOUT is not activated. A full sequence of voltage
measurements nominally takes 1760ms to complete.
DS2786B
Stand-Alone OCV-Based Fuel Gauge
_______________________________________________________________________________________ 9
Voltage Measurement
Battery voltage is measured at the VIN input with respect
to VSS over 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 VIN is 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 VIN input.
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 Measurements
The 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 VOUT pin 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 2
10 2
9 2
8 2
7 2
6 2
5 2
4 2
3 2
2 2
1 2
0 X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: 1.22mV
Figure 5. Voltage Register Format
AIN0 MSB—ADDRESS 08h LSB—ADDRESS 09h
S 210 2
9 2
8 2
7 2
6 2
5 2
4 2
3 2
2 2
1 2
0 X X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: VOUT × 1/2047
AIN1 MSB—ADDRESS 0Ah LSB—ADDRESS 0Bh
S 210 2
9 2
8 2
7 2
6 2
5 2
4 2
3 2
2 2
1 2
0 X X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: VOUT × 1/2047
Figure 6. Auxiliary Input Registers Format
DS2786B
Stand-Alone OCV-Based Fuel Gauge
10 ______________________________________________________________________________________
MSB—ADDRESS 0Ah LSB—ADDRESS 0Bh
S 29 2
8 2
7 2
6 2
5 2
4 2
3 2
2 2
1 2
0 X X X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: 0.125°C
Figure 7. Temperature Register Format
MSB—ADDRESS 0Eh LSB—ADDRESS 0Fh
S 210 2
9 2
8 2
7 2
6 2
5 2
4 2
3 2
2 2
1 2
0 X X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: 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
RSNS
VSS - VSNS 20m 15m 10m 5m
±51.2mV ±2.56A ±3.41A ±5.12A ±10.24A
Table 1. Current Range and Resolution for Various RSNS Values
Temperature Measurement
The 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 Measurement
In the Active Mode of operation, the DS2786B continu-
ally measures the current flow into and out of the bat-
tery by measuring the voltage drop across a low-value
current-sense resistor, RSNS, connected between the
SNS and VSS pins. The voltage-sense range between
SNS and VSS is ±51.2mV. Note that positive current val-
ues occur when VSNS is less than VSS, and negative
current values occur when VSNS is 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
RSNS values.
DS2786B
Stand-Alone OCV-Based Fuel Gauge
______________________________________________________________________________________ 11
Current Offset Bias
The Current Offset Bias Register (COBR) allows a pro-
grammable offset value to be added to raw current
measurements. The result of the raw current measure-
ment plus the COBR value is displayed as the current
measurement result in the Current Register, and is used
for current accumulation and detection of an OCV con-
dition. The COBR value can be used to correct for a sta-
tic offset error, or can be used to intentionally skew the
current results and therefore the current accumulation.
Read and write access is allowed to COBR. Whenever
the COBR is written, the new value is applied to all sub-
sequent current measurements. COBR can be pro-
grammed in 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 Accumulation
An Internal Accumulated Current Register (IACR)
serves as an up/down counter holding a running count
of charge since the last OCV condition. Current mea-
surement results, plus a programmable bias value are
internally summed, or accumulated, at the completion
of each current measurement-conversion period. The
IACR has a range of ±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 RSNS values.
Cell-Capacity Estimation
The 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 2
5 2
4 2
3 2
2 2
1 2
0
MSB LSB
“S”: SIGN BIT UNITS: 25μV/RSNS
Figure 9. Current Offset Bias Register Format
IACR RANGE
RSNS
VSS - VSNS 20m 15m 10m 5m
±204.8mVh ±10.24Ah ±13.65Ah ±20.48Ah ±40.96Ah
Table 2. Accumulated Current Range for
Various RSNS Values
ADDRESS 02h
27 2
6 2
5 2
4 2
3 2
2 2
1 2
0
MSB LSB
UNITS: 0.5%
Figure 10. Relative Capacity Register Format
DS2786B
Stand-Alone OCV-Based Fuel Gauge
12 ______________________________________________________________________________________
Prior to the first learn operation, the relative capacity
value is calculated by adding the IACR multiplied by the
initial capacity scaling factor (7Ah) to the last OCV rela-
tive capacity (16h). After the first learn operation, the rel-
ative capacity value is calculated by adding the IACR
multiplied by the learned capacity scaling factor (17h) to
the last OCV relative capacity (16h).
Each Capacity Scaling Factor Register has a resolution
of 78.125%/Vh and a maximum range of 0 to
19921.875%/Vh. During assembly, the Initial Capacity
Register should be programmed to the capacity of the
cell. For example, an application using a 1Ah cell and
0.015Ωsense resistor would set the Initial Capacity
Register to a value of (100%/(1Ah x 0.015Ω))/
78.125%/Vh = 55h. The Learned Capacity Scaling Factor
Register is controlled by the DS2786B. The power-up
value is 00h, and the register is updated with the calcu-
lated new cell capacity value after every learn operation.
See Figures 11 and 12.
OCV Detection
When the magnitude of the measured current (after
COBR is applied) is less than the value defined by the
OCV Threshold Register, the DS2786B begins dV/dt
measurement evaluation to detect an OCV voltage
condition. A threshold value that is below the minimum
operational current, but above the maximum idle cur-
rent of the application should be selected. The OCV
Threshold Register has a resolution of 25µV/RSNS, and
a range from 0mV/RSNS to 6.375mV/RSNS. The factory
default value is 28h. See Figure 13 for the OCV thresh-
old register format.
While the measured current is below the OCV threshold
level, the DS2786B actively searches for a relaxed cell
by calculating the change in cell voltage as reported in
the Voltage Register over 7.5min intervals (dV/dt). If the
7.5min dV/dt change of an average of four Voltage
Register readings is less than the value stored in the
OCV dV/dt Threshold Register, the DS2786B deter-
mines that the cell is now in a relaxed state and the
Relative Capacity Register is adjusted based on the
OCV cell model stored in parameter EEPROM. This
operation occurs repeatedly every 7.5min up to 1hr
after the cell enters a relaxed state.
The OCV dV/dt Threshold Register has a resolution of
0.61mV/7.5min and a range from 0mV/7.5min to
9.15mV/7.5min. The factory default value is
2.44mV/7.5min. Note that the upper 4 bits of the OCV
dV/dt Threshold Register are used to EEPROM back
bits from the Status/Configuration Register. Figure 14
shows the OCV dV/dt threshold register format.
ADDRESS 7Ah
27 2
6 2
5 2
4 2
3 2
2 2
1 2
0
MSB LSB
UNITS: 78.125%/Vh
Figure 11. Initial Capacity Scaling Factor Register Format
ADDRESS 17h
27 2
6 2
5 2
4 2
3 2
2 2
1 2
0
MSB LSB
UNITS: 78.125%/Vh
Figure 12. Learned Capacity Scaling Factor Register Format
ADDRESS 7Bh
27 2
6 2
5 2
4 2
3 2
2 2
1 2
0
MSB LSB
UNITS: 25μV/RSNS
Figure 13. OCV Threshold Register Format
ADDRESS 7Ch
SMOD LDIS VODIS ITEMP 23 2
2 2
1 2
0
MSB LSB
UNITS: 0.61mV/7.5min
Figure 14. OCV dV/dt Threshold Register Format
DS2786B
Stand-Alone OCV-Based Fuel Gauge
______________________________________________________________________________________ 13
OCV Cell Model
The OCV cell model is a 9-point piece-wise linear
approximation of open-circuit cell voltage vs. the
remaining capacity of the cell. Whenever an OCV
update occurs, the Relative Capacity Register is adjust-
ed to a new value based on the OCV voltage reading
and a linear approximation of the table values. Figure 15
shows the factory-default cell model stored in EEPROM.
The OCV cell model can be modified by changing the
Capacity and Voltage Breakpoint Registers in EEPROM.
Capacity 0 is fixed at 0% and cannot be changed.
Capacity 1 through Capacity 7 are stored with 0.5%
resolution at addresses 61h through 67h, respectively.
Capacity values must be monotonic (Capacity 1 >
Capacity 0, Capacity 2 > Capacity 1, etc.), but other-
wise can be written to any value between 0.5% to
99.5%. Capacity 8 is fixed at a value of 100% and can-
not be changed. See Figure 16.
Voltage breakpoints require 2 bytes per breakpoint, but
are otherwise stored in a similar manner: voltage break-
point 0: MSB stored at address 68h, LSB stored at
address 69h. Other voltage breakpoints are stored
sequentially through address location 79h. Each volt-
age breakpoint has a resolution of 1.22mV, and a range
from 0.0V to 4.996V. Voltage breakpoint values must
also be monotonic. Figure 17 is the Voltage Breakpoint
Register format.
3.0
3.2
3.4
3.6
3.8
4.0
4.2
0%20%40%60%80%100%
BREAKPOINT 8
4.171V
100%
BREAKPOINT 6
4.042V
85%
BREAKPOINT 5
4.005V
80% BREAKPOINT 3
3.752V
25% BREAKPOINT 1
3.619V
5%
BREAKPOINT 0
3.186V
0%
BREAKPOINT 7
4.087V
90.5%
BREAKPOINT 4
3.831V
52.5% BREAKPOINT 2
3.673V
10%
Figure 15. DS2786BG-C3 OCV Cell Model
ADDRESS 61h–67h
27 2
6 2
5 2
4 2
3 2
2 2
1 2
0
MSB LSB
UNITS: 0.5%
Figure 16. Capacity 1 to Capacity 7 Registers Format
DS2786B
Stand-Alone OCV-Based Fuel Gauge
14 ______________________________________________________________________________________
MSB—EVEN ADDRESSES 68h–78h LSB—ODD ADDRESS 69h–79h
211 2
10 2
9 2
8 2
7 2
6 2
5 2
4 2
3 2
2 2
1 2
0 X X X X
MSB LSB MSB LSB
“X”: RESERVED UNITS: 1.22mV
Figure 17. Voltage Breakpoint Register Format
MSB—ADDRESS 14h LSB—ADDRESS 15h
S 211 2
10 2
9 2
8 2
7 2
6 2
5 2
4 2
3 2
2 2
1 2
0 X X X
MSB LSB MSB LSB
“S”: SIGN BIT, “X”: RESERVED UNITS: 1.22mV
Figure 18. Initial Voltage Register Format
ADDRESS 16h
27 2
6 2
5 2
4 2
3 2
2 2
1 2
0
MSB LSB
UNITS: 0.5%
Figure 19. Last OCV Register Format
Initial Capacity Estimation
The DS2786B calculates relative capacity immediately
upon power-up. During initialization, the DS2786B
makes a voltage measurement and uses the OCV cell
model data to determine a starting point for the Relative
Capacity Register. This estimation occurs regardless of
the load on the cell. Any error induced from cell loading
is removed at the next OCV adjustment. The initial volt-
age measurement used in determining the starting
point is stored in the Initial Voltage Register until the IC
is power cycled. See Figure 18.
New Capacity Learning
As the cell ages, the Initial Capacity Scaling Factor
Register value might no longer accurately reflect the
true capacity of the cell, causing error in relative capaci-
ty calculation while in coulomb-counting mode of opera-
tion. The DS2786B has a learn feature that allows the IC
to remain accurate as the cell changes. The DS2786B
compares the percent relative capacity difference
between the last two OCV updates to the change in the
coulomb count to learn the new cell capacity. The Last
OCV Register maintains the relative capacity percent-
age at the previous OCV adjustment point used for
learning the new cell capacity. The last OCV is updated
with a new value at each OCV adjustment. Figure 19
shows the Last OCV Register format.
Example: Assuming a 15mΩsense resistor, the
DS2786B adjusts the relative capacity of a 1000mAh
cell to 10% based on an OCV measurement during an
idle period of the application. The cell is then charged
by 500mAh (to 60% expected) based on the internal
coulomb count multiplied by the learned capacity scal-
ing factor value of 55h. The next OCV adjustment deter-
mines the relative capacity should actually be at 65%,
not 60%. The DS2786B then adjusts the learned capac-
ity scaling factor value upward to (65% - 10%)/(500mAh
x 0.015Ω) = 5Eh, lowering the expected cell capacity
by approximately 10%.
DS2786B
Stand-Alone OCV-Based Fuel Gauge
______________________________________________________________________________________ 15
The learn delta percent threshold allows the application
to select how large a cell capacity change is required
before the new cell-capacity value is learned. The dif-
ference between the present OCV measurement and
the last OCV measurement must be greater than the
learn delta percent threshold value for a learn to occur.
This prevents IC measurement resolution from adding
error to the learned cell-capacity value. It is recom-
mended this register be set to a value of at least 50%.
Figure 20 shows the learn delta percent threshold.
Memory Map
The DS2786B has memory space with registers for instru-
mentation, status, and control. When the MSB of a 2-byte
register is read, both the MSB and LSB are latched and
held for the duration of the read data command to pre-
vent updates during the read and ensure synchronization
between the 2 register bytes. For consistent results,
always read the MSB and the LSB of a 2-byte register
during the same read data command sequence.
Memory locations 60h through 7Fh are EEPROM stor-
age locations. EEPROM memory is shadowed by RAM
to eliminate programming delays between writes and to
allow the data to be verified by the host system before
being copied to EEPROM. The read data and write data
protocols to/from EEPROM memory addresses access
the shadow RAM. Setting the RCALL bit in the
Command Register (FEh) initiates data transfer from the
EEPROM to the shadow RAM. See Figure 21.
Setting the COPY bit in the Command Register initiates
data transfer from the shadow RAM to the EEPROM. An
external voltage supply must be provided on the
VPROG pin prior to writing the COPY bit. The DS2786B
requires the COPY bit be reset to zero within the tPROG
time window to properly program EEPROM. Resetting
COPY too soon might prevent a proper write of the
cells. Resetting COPY too late might degrade EEPROM
copy endurance.
The DS2786B uses shadow RAM data for fuel-gauge
calculations. Fuel-gauge information can be changed in
the application by writing the shadow RAM locations.
Afterwards, the SOCV bit should be written to reset the
fuel gauge. Note that any reset of the IC causes the
shadow RAM data to be restored from EEPROM.
ADDRESS 7Eh
27 2
6 2
5 2
4 2
3 2
2 2
1 2
0
MSB LSB
UNITS: 0.5%
Figure 20. Learn Delta Percent Threshold
SHADOW
EEPROM
WRITE
RECALL
COPY
READ
SERIAL
INTERFACE
Figure 21. EEPROM Access Through Shadow RAM
DS2786B
Stand-Alone OCV-Based Fuel Gauge
16 ______________________________________________________________________________________
ADDRESS DESCRIPTION READ/WRITE
00h Reserved —
01h Status/Config Register R/W
02h Relative Capacity R
03h to 07h Reserved —
08h Auxiliary Input 0 MSB R
09h Auxiliary Input 0 LSB R
0Ah Auxiliary Input 1/
Temperature MSB R
0Bh Auxiliary Input 1/
Temperature LSB R
0Ch Voltage Register MSB R
0Dh Voltage Register LSB R
0Eh Current Register MSB R
ADDRESS DESCRIPTION READ/WRITE
0Fh Current Register LSB R
10h to 13h Reserved —
14h Initial Voltage MSB R
15h Initial Voltage LSB R
16h Last OCV Relative
Capacity R
17h Learned Capacity
Scaling Factor R
18h to 5Fh Reserved —
60h to 7Fh Parameter EEPROM R/W
80h to FDh Reserved —
FEh Command R/W
FFh Reserved —
Table 3. Memory Map
ADDRESSS DESCRIPTION FACTORY
VALUE
60h Current Offset Bias Register 00h
61h Capacity 1 0Ah
62h Capacity 2 14h
63h Capacity 3 32h
64h Capacity 4 69h
65h Capacity 5 A0h
66h Capacity 6 AAh
67h Capacity 7 B5h
68h Voltage Breakpoint 0 MSB A3h
69h Voltage Breakpoint 0 LSB 20h
6Ah Voltage Breakpoint 1 MSB B9h
6Bh Voltage Breakpoint 1 LSB 50h
6Ch Voltage Breakpoint 2 MSB BCh
6Dh Voltage Breakpoint 2 LSB 10h
6Eh Voltage Breakpoint 3 MSB C0h
6Fh Voltage Breakpoint 3 LSB 20h
ADDRESS DESCRIPTION FACTORY
VALUE
70h Voltage Breakpoint 4 MSB C4h
71h Voltage Breakpoint 4 LSB 20h
72h Voltage Breakpoint 5 MSB CDh
73h Voltage Breakpoint 5 LSB 10h
74h Voltage Breakpoint 6 MSB CEh
75h Voltage Breakpoint 6 LSB F0h
76h Voltage Breakpoint 7 MSB D1h
77h Voltage Breakpoint 7 LSB 40h
78h Voltage Breakpoint 8 MSB D5h
79h Voltage Breakpoint 8 LSB 90h
7Ah Initial Capacity Scaling 80h
7Bh OCV Current Threshold 06h
7Ch OCV dV/dt Threshold 94h
7Dh I2C Address Configuration* 60h*
7Eh Learn Threshold 78h
7Fh User EEPROM 00h
Table 4. Parameter EEPROM Memory Block
*
The factory default 7-bit slave address is 0110110. The upper 3 bits are fixed at 011; the lower 4 bits can be changed by writing the
I2C Address Configuration Register as illustrated in Figures 24 and 25.
DS2786B
Stand-Alone OCV-Based Fuel Gauge
______________________________________________________________________________________ 17
Status/Config Register
The Status/Config Register is read/write with individual
bits designated as read only. Bit values indicate status as
well as program or select device functionality. Bits 3
though 6 are EEPROM backed at memory location 7Ch.
Note that their bit positions differ between these locations.
See Figure 22:
• PORF—The power-on-reset flag is set to indicate
initial power-up. PORF is not cleared internally. The
user must write this flag value to a zero in order to
use it to indicate subsequent power-up events. POR
event causes a reset of the fuel gauge. PORF is
read/write-to-zero.
• SMOD—Sleep Mode enable. A value of 1 allows the
IC to enter Sleep Mode when SCL and SDA are low
for tSLEEP. A value of zero disables the transition to
Sleep Mode. This bit is EEPROM backed by bit 7 of
memory location 7Ch. The factory-programmed
value is 1.
Caution: SMOD sleep feature must be disabled
when a battery is charged on an external charger
that does not connect to the SDA or SCL pins.
SMOD sleep can be used if the charger pulls SDA
or SCL high. The IC remains in sleep on a charger
that fails to properly drive SDA or SCL and therefore
does not adjust relative capacity when a battery is
charged.
• LDIS—Learn disable. A value of 1 disables cell-
capacity learning by the IC. A value of zero allows
cell-capacity learning to occur normally. This bit is
EEPROM backed by bit 6 of memory location 7Ch.
The factory-programmed value is zero.
• VODIS—VOUT disable. A value of 1 disables the
VOUT output. When set to zero, this output is driven
tPRE before the AIN0 conversion begins, and dis-
abled after the AIN1 conversion ends. This bit is
EEPROM backed by bit 5 of memory location 7Ch.
The factory-programmed value is zero.
• ITEMP—ITEMP. A value of 1 enables measurement
of temperature using the internal sensor during the
AIN1 conversion timeslot. The AIN1 input is not
selected and VOUT is not enabled during the AIN1
timeslot. A value of zero restores the measurement
of AIN1 and enables VOUT during the AIN1 timeslot.
This bit is EEPROM backed by bit 4 of memory
location 7Ch. The factory-programmed value is 1.
• AIN1—AIN1 conversion valid. This read-only bit
indicates that the VOUT output was enabled and a
conversion has occurred on the AIN1 pin. When
using the VODIS bit, before reading the AIN1
Registers, read the AIN1 bit. Only once the AIN1 bit
is set should the AIN1 Register be read.
• AIN0—AIN0 conversion valid. This read-only bit
indicates that the VOUT output was enabled and a
conversion has occurred on the AIN0 pin. When
using the VODIS bit, before reading the AIN0
Registers, read the AIN0 bit. Only once the AIN0 bit
is set should the AIN0 Register be read.
Command Register
The Command Register is read/write accessible. Bit val-
ues indicate operations requested to be performed by the
device. See Figure 23 for the Command Register format.
ADDRESS 01h
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
X PORF SMOD LDIS VODIS ITEMP AIN1 AIN0
X—Reserved.
Figure 22. Status/Config Register Format
ADDRESS FEh
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
POR 1 X X POCV SOCV RCALL COPY
1—Bit always reads logic 1.
X—Reserved.
Figure 23. Command Register Format
DS2786B
Stand-Alone OCV-Based Fuel Gauge
18 ______________________________________________________________________________________
• COPY—The Copy bit is set to start a copy command
of the scratchpad to EEPROM. A programming volt-
age must be present on the VPROG pin prior for the
copy to be successful. The Copy bit must be cleared
by software within the tPROG time window.
• RCALL—The Recall bit is set to recall the contents
of EEPROM into the scratchpad.
• SOCV—Stored OCV calculation. This command can
be used to reset the relative capacity calculation
after updating OCV cell model data in the scratch-
pad. When set to 1, the part is performing an OCV
calculation based on the voltage stored in the Initial
Voltage Register and the OCV lookup table values
present in the scratchpad. Writing the bit to 1 forces
a calculation. Forcing an OCV calculation creates
capacity-estimation error. The bit is cleared when
the hardware completes the calculation.
• POCV—Present OCV calculation. When set to 1,
the part is performing an OCV calculation based on
the voltage stored in the Voltage Register and the
OCV lookup table values present in the scratchpad.
Writing the bit to 1 forces a calculation. This func-
tion should be used for test purposes only. Forcing
an OCV calculation creates capacity-estimation
error. The bit is cleared when the hardware com-
pletes the calculation.
• POR—Power-on reset. A value of 1 starts a power-
on reset event. The bit is cleared on the next start or
stop on the 2-wire bus, exiting the reset state.
User EEPROM
Location 7Fh provides 1 byte available for storage of
user-defined information. This byte does not affect
operation of the fuel gauge. Factory default is 00h.
2-Wire Bus System
The 2-wire bus system supports operation as a slave-
only device in a single or multislave, and single or multi-
master system. The 2-wire interface consists of a serial
data line (SDA) and serial clock line (SCL). SDA and
SCL provide bidirectional communication between the
DS2786B slave device and a master device at speeds
up to 400kHz. The DS2786B’s SDA pin operates bidi-
rectionally; that is, when the DS2786B receives data,
SDA operates as an input, and when the DS2786B
returns data, SDA operates as an open-drain output,
with the host system providing a resistive pullup. The
DS2786B always operates as a slave device, receiving
and transmitting data under the control of a master
device. The master initiates all transactions on the bus
and generates the SCL signal, as well as the START
and STOP bits, which begin and end each transaction.
Bit Transfer
One data bit is transferred during each SCL clock
cycle, with the cycle defined by SCL transitioning low to
high and then high to low. The SDA logic level must
remain stable during the high period of the SCL clock
pulse. Any change in SDA when SCL is high is inter-
preted as a START or STOP control signal.
Bus Idle
The bus is defined to be idle, or not busy, when no
master device has control. Both SDA and SCL remain
high when the bus is idle. The STOP condition is the
proper method to return the bus to the idle state.
START and STOP Conditions
The master initiates transactions with a START condi-
tion (S) by forcing a high-to-low transition on SDA while
SCL is high. The master terminates a transaction with a
STOP condition (P), a low-to-high transition on SDA
while SCL is high. A Repeated START condition (Sr)
can be used in place of a STOP then START sequence
to terminate one transaction and begin another without
returning the bus to the idle state. In multimaster sys-
tems, a Repeated START allows the master to retain
control of the bus. The START and STOP conditions are
the only bus activities in which the SDA transitions
when SCL is high.
Acknowledge Bits
Each byte of a data transfer is acknowledged with an
Acknowledge bit (A) or a No Acknowledge bit (N). Both
the master and the DS2786B slave generate
Acknowledge bits. To generate an acknowledge, the
receiving device must pull SDA low before the rising
edge of the acknowledge-related clock pulse (ninth
pulse) and keep it low until SCL returns low. To gener-
ate a no acknowledge (also called NAK), the receiver
releases SDA before the rising edge of the acknowl-
edge-related clock pulse and leaves SDA high until
SCL returns low. Monitoring the Acknowledge bits
allows for detection of unsuccessful data transfers. An
unsuccessful data transfer can occur if a receiving
device is busy or if a system fault has occurred. In the
event of an unsuccessful data transfer, the bus master
should reattempt communication.
Data Order
A byte of data consists of 8 bits ordered MSB first. The
LSB of each byte is followed by the Acknowledge bit.
The DS2786B registers composed of multibyte values
are ordered MSB first. The MSB of multibyte registers is
stored on even data memory addresses.
DS2786B
Stand-Alone OCV-Based Fuel Gauge
______________________________________________________________________________________ 19
Slave Address
A bus master initiates communication with a slave
device by issuing a START condition followed by a
slave address (SAddr) and the read/write (R/W) bit.
When the bus is idle, the DS2786B continuously moni-
tors for a START condition followed by its slave
address. When the IC receives an address that match-
es its slave address, it responds with an Acknowledge
bit during the clock period following the R/W bit. The
DS2786BG-C3 7-bit slave address is 0110110. The
upper 3 bits are fixed at 011; the lower 4 bits can be
changed by writing the I2C Address Configuration
Register at location 7Dh.
Read/Write Bit
The R/W bit following the slave address determines the
data direction of subsequent bytes in the transfer. R/W
= 0 selects a write transaction, with the following bytes
being written by the master to the slave. R/W = 1 selects
a read transaction, with the following bytes being read
from the slave by the master. With the ADDR3–ADDR0
bits at their default of 0110, writes occur using address
0x6Ch, while reads occur at 0x6Dh.
Bus Timing
The DS2786B is compatible with any bus timing up to
400kHz. No special configuration is required to operate
at any speed.
2-Wire Command Protocols
The command protocols involve several transaction for-
mats. The simplest format consists of the master writing
the START bit, slave address, and R/W bit, and then
monitoring the Acknowledge bit for presence of the
DS2786B. More complex formats such as the write
data, read data, and function command protocols write
data, read data, and execute device-specific opera-
tions. All bytes in each command format require the
slave or host to return an Acknowledge bit before con-
tinuing with the next byte. Each function command defi-
nition outlines the required transaction format. Table 5
applies to the transaction formats.
ADDRESS 7Dh
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
ADDR3 ADDR2 ADDR1 ADDR0 X X X X
X—RESERVED.
ADDR3:0—USER-ADJUSTABLE BITS OF THE DS2786BG-C3’S I2C ADDRESS. FACTORY DEFAULT IS 0110.
Figure 24. I2C Address Configuration Register Format
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0 1 1 ADDR3 ADDR2 ADDR1 ADDR0 R/W
Figure 25. DS2786B I2C Address Byte Format
KEY DESCRIPTION
S START bit
SAddr Slave address (7 bit)
FCmd Function command byte
MAddr Memory address byte
Data Data byte written by master
A Acknowledge bit—master
N No acknowledge—master
KEY DESCRIPTION
Sr Repeated START
W R/W bit = 0
R R/W bit = 1
P STOP bit
Data Data byte returned by slave
A Acknowledge bit—slave
N No acknowledge—slave
Table 5. 2-Wire Protocol Key
DS2786B
Stand-Alone OCV-Based Fuel Gauge
20 ______________________________________________________________________________________
Basic Transaction Formats
Write: S SAddr W A MAddr A Data0 A P
A write transaction transfers 1 or more data bytes to the
DS2786B. The data transfer begins at the memory
address supplied in the MAddr byte. Control of the SDA
signal is retained by the master throughout the transac-
tion, except for the acknowledge cycles.
A read transaction transfers 1 or more bytes from the
DS2786B. Read transactions are composed of two
parts—a write portion followed by a read portion—and
are therefore inherently longer than a write transaction.
The write portion communicates the starting point for
the read operation. The read portion follows immediate-
ly, beginning with a Repeated START, Slave Address
with R/W set to 1. Control of SDA is assumed by the
DS2786B beginning with the Slave Address
Acknowledge cycle. Control of the SDA signal is
retained by the DS2786B throughout the transaction,
except for the acknowledge cycles. The master indi-
cates the end of a read transaction by responding to
the last byte it requires with a no acknowledge. This
signals the DS2786B that control of SDA is to remain
with the master following the acknowledge clock.
Write Data Protocol
The write data protocol is used to write to register and
shadow RAM data to the DS2786B starting at memory
address MAddr. Data0 represents the data written to
MAddr, Data1 represents the data written to MAddr +
1, and DataN represents the last data byte, written to
MAddr + N. The master indicates the end of a write
transaction by sending a STOP or Repeated START
after receiving the last acknowledge bit:
S SAddr W A MAddr A Data0 A Data1 A … DataN A P
The MSB of the data to be stored at address MAddr
can be written immediately after the MAddr byte is
acknowledged. Because the address is automatically
incremented after the LSB of each byte is received by
the DS2786B, the MSB of the data at address MAddr +
1 can be written immediately after the acknowledgment
of the data at address MAddr. If the bus master contin-
ues an autoincremented write transaction beyond
address 4Fh, the DS2786B ignores the data. Data is
also ignored on writes to read-only addresses and
reserved addresses, as well as a write that autoincre-
ments to the Function Command Register (address
FEh). Incomplete bytes and bytes that are not acknowl-
edged by the DS2786B are not written to memory. As
noted in the
Memory Map
section, writes to EEPROM
locations modify the shadow RAM only.
Read Data Protocol
The read data protocol is used to read register and
shadow RAM data from the DS2786B starting at memo-
ry address specified by MAddr. Data0 represents the
data byte in memory location MAddr, Data1 represents
the data from MAddr + 1, and DataN represents the
last byte read by the master:
S SAddr W A MAddr A Sr SAddr R A Data0 A Data1
...DataN N P
Data is returned beginning with the MSB of the data in
MAddr. Because the address is automatically incre-
mented after the LSB of each byte is returned, the MSB
of the data at address MAddr + 1 is available to the
host immediately after the acknowledgment of the data
at address MAddr. If the bus master continues to read
beyond address FFh, the DS2786B outputs data values
of FFh. Addresses labeled Reserved in the memory
map (Table 3) return undefined data. The bus master
terminates the read transaction at any byte boundary
by issuing a no acknowledge followed by a STOP or
Repeated START.
Package Information
For the latest package outline information and land patterns,
go to www.maxim-ic.com/packages. Note that a “+”, “#”, or
“-” in the package code indicates RoHS status only. Package
drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
Read: SAddr W A MAddr A Sr SAddr R A Data0 N P
Write Portion Read Portion
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
10 TDFN T1033+1 21-0137
DS2786B
Stand-Alone OCV-Based Fuel Gauge
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________
21
© 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 7/08 Initial release —
1 4/10
Changed the maximum operating voltage on VDD to 4.5V in the Features,Electrical
Characteristics, and Pin Description sections 1–5
