DS2786 [MAXIM]
Standalone OCV-Based Fuel Gauge; 独立的基于OCV电量计
| 型号： | DS2786 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Standalone OCV-Based Fuel Gauge |
| 文件： | 总21页 (文件大小：348K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
DS2786
Standalone OCV-Based Fuel Gauge
www.maxim-ic.com
FEATURES
GENERAL DESCRIPTION
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
The DS2786 estimates available capacity for
rechargeable Li-Ion and Li-Ion Polymer batteries
based on the cell voltage in the open-circuit state
following a relaxation 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 discharging,
which preclude OCV measurements, the DS2786
uses coulomb counting as a secondary means of
estimating relative capacity.
1.22mV LSB, 0V to 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 Aux Input Voltage Measurements:
±8 LSB Accuracy, Ratiometric Inputs
Eliminate Supply Accuracy Issues
VOUT Pin Drives Resistive Dividers, Reduces
Current Consumption
2-Wire Interface
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 DS2786 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 measurements of a pack identification
resistor and pack thermistor are supported by
ratiometric measurements on two auxiliary inputs.
Low Power Consumption:
Active Current: 50μA typ, 80μA max
Sleep Current: 1μA typ, 3μA max
ORDERING INFORMATION
APPLICATIONS
PART
TEMP RANGE
PIN-PACKAGE
10-pin 3mm×3mm
TDFN
3G Multimedia Wireless Handsets
Digital Still Cameras
DS2786G+
-20ºC to +70ºC
Digital Audio (MP3) Players
DS2786G+ in
Tape-and-Reel
DS2786G+T&R
-20ºC to +70ºC
+ Denotes lead-free package.
TYPICAL OPERATING CIRCUIT
PIN CONFIGURATION
3mm x 3mm TDFN-10
Top View
Commands, Registers, and Modes are capitalized for clarity.
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050907
DS2786 Standalone OCV-Based Fuel Gauge
ABSOLUTE MAXIMUM RATINGS*
Voltage on All Pins Except VPROG Relative to VSS
Voltage on VPROG Relative to VSS
Operating Temperature Range
-0.3V to +6V
-0.3V to +18V
-40°C to +85°C
Storage Temperature Range
Soldering Temperature
-55°C to +125°C
See IPC/JEDECJ-STD-020A
* This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the
operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of
time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
(2.5V ≤ VDD ≤ 5.5V, TA = -20°C to +70°C.)
PARAMETER
SYMBOL
CONDITIONS
(Note 1)
MIN
+2.5
-0.3
-0.3
TYP
MAX
+5.5
+5.5
+5.5
UNITS
Supply Voltage
VDD
V
V
V
Data I/O Pins
SCL, SDA (Note 1)
Programmable I/O Pin
PIO
VIN, AIN0,
AIN1
(Note 1)
VIN, AIN0, AIN1 Pin
(Note 1)
-0.3
VDD + 0.3
V
DC ELECTRICAL CHARACTERISTICS
(2.5V ≤ VDD ≤ 4.5V, TA = -20°C to +70°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
50
75
Active Current
IACTIVE
μA
V
DD = 5.5V
80
1.0
3
VDD = 2.0V,
SCL, SDA = VSS
0.3
1
Sleep-Mode Current
ISLEEP
μA
SCL, SDA = VSS
DS2786
Current Measurement
Resolution
Current Measurement
Full-Scale Magnitude
Current Measurement
Offset Error
ILSB
IFS
IOERR
IGERR
25
μV
mV
μV
(Note 1)
±51.2
DS2786 (Note 2)
-50
-1.5
-1
+50
+1.5
+1
Current Measurement
Gain Error
% of
reading
VDD = 3.6V at +25°C
TA = 0°C to +70°C
TA = -20°C to +70°C
Timebase Accuracy
tERR
%
-2
+2
-3
+3
VDD = VIN = 3.6V,
TA = 0°C to +50°C
-10
-20
+10
+20
Voltage Error
VGERR
mV
TA = -20°C to +70°C
Input Resistance
VIN, AIN0, AIN1
RIN
15
-8
MΩ
LSB
V
AIN0, AIN1 Error
+8
VOUT Output Drive
VOUT Precharge Time
Temperature Error
IO = 1mA
VDD - 0.5
13.7
tPRE
13.2
-3
14.2
+3
ms
°C
TERR
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DS2786 Standalone OCV-Based Fuel Gauge
Input Logic High:
SCL, SDA
Input Logic Low:
SCL, SDA
Output Logic Low:
SDA
Pulldown Current:
SCL, SDA
VIH
VIL
(Note 1)
1.4
V
V
V
(Note 1)
0.6
0.4
1.0
VOL
IOL = 4mA (Note 1)
VDD = 4.2V,
VPIN = 0.4V
IPD
0.2
20
μA
kΩ
VPROG Pulldown
RVPROG
Input Capacitance:
SCL, SDA
CBUS
tSLEEP
VPROG
50
2.2
15
pF
S
Bus Low Timeout
(Note 3)
1.5
14
EEPROM Programming
Voltage
V
EEPROM Programming
Current
EEPROM Programming
Time
IPROG
tPROG
2
mA
ms
3.1
14
EEPROM Copy
Endurance
100
writes
ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE
(2.5V ≤ VDD ≤ 5.5V, TA = -20°C to +70°C.)
PARAMETER
SYMBOL
CONDITIONS
(Note 4)
MIN
TYP
MAX
UNITS
fSCL
SCL Clock Frequency
0
400
kHz
Bus Free Time Between
a STOP and START
Condition
tBUF
1.3
µs
Hold Time (Repeated)
START Condition
tHD:STA
tLOW
(Note 5)
0.6
1.3
0.6
µs
µs
µs
Low Period of SCL Clock
High Period of SCL Clock
tHIGH
Setup Time for a
Repeated
tSU:STA
0.6
µs
START Condition
tHD:DAT
tSU:DAT
tR
Data Hold Time
Data Setup Time
(Notes 6, 7)
(Note 6)
0
0.9
µs
ns
ns
ns
µs
100
Rise Time of Both SDA
and SCL Signals
Fall Time of Both SDA
and SCL Signals
Setup Time for STOP
Condition
20 + 0.1CB
20 + 0.1CB
0.6
300
300
tF
tSU:STO
Spike Pulse Widths
Suppressed by Input
Filter
Capacitive Load for Each
Bus Line
tSP
(Note 8)
(Note 9)
0
50
ns
CB
400
60
pF
pF
SCL, SDA Input
Capacitance
CBIN
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DS2786 Standalone OCV-Based Fuel Gauge
Note 1:
Note 2:
Note 3:
Note 4:
All voltages are referenced to VSS.
Offset specified after auto-calibration cycle and Current Offset Bias Register = 00h.
The DS2786 enters the Sleep mode 1.5s to 2.2s after (SCL < VIL) AND (SDA < VIL).
Timing must be fast enough to prevent the DS2786 from entering Sleep mode due to bus low for period
> tSLEEP
.
Note 5:
Note 6:
fSCL must meet the minimum clock low time plus the rise/fall times.
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.
Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant.
CB—total capacitance of one bus line in pF.
Note 8:
Note 9:
Figure 1. 2-Wire Bus Timing Diagram
PIN DESCRIPTION
PIN
NAME
FUNCTION
1
2
AIN1
AIN0
Aux Voltage Input Number 1
Aux Voltage Input Number 0
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.
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.
3
SCL
4
SDA
5
6
SNS
VSS
Current-Sense Input. Connect to the handset side of the sense resistor.
Device Ground. Connect to the battery side of the sense resistor.
EEPROM Programming Voltage Input. Connect to external supply for production
programming. Connect to VSS during normal operation.
7
VPROG
Voltage Out. Supply for Aux Input Voltage Measurement Dividers. Connect to high side
of resistor divider circuits.
Battery Voltage Input. The voltage of the cell pack is measured through this pin.
Power-Supply Input. 2.5V to 5.5V input range. Connect to system power through a
decoupling network.
8
9
VOUT
VIN
10
VDD
PAD
PAD
Exposed Pad. Connect to VSS.
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DS2786 Standalone OCV-Based Fuel Gauge
Figure 2. Block Diagram
DESCRIPTION
The DS2786 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 15mΩ sense resistor, the current sense range is ±3.4A, with a 1 LSB resolution
of 1.667mA. Current measurements are performed at regular intervals and accumulated with each measurement to
support “coulomb counting” during periods of host power consumption. Each current measurement is reported with
sign and magnitude in the two-byte Current Register. Battery voltage measurements are reported in the two-byte
Voltage Register with 12-bit (1.22mV) resolution, and auxiliary voltage measurements are reported in the two-byte
Aux Volt Registers with 11-bit resolution. Additionally, the Temperature Register reports temperature with 0.125ºC
resolution and ±3ºC accuracy from the on-chip sensor. The on-chip temperature measurement is optional and
replaces the auxiliary voltage channel AIN1.
The DS2786 provides accurate relative capacity measurements during periods of host system inactivity by looking
at cell open circuit voltage. Cell capacity is calculated using an OCV voltage profile and a 1-byte scale factor to
weight accumulated current during the coulomb-counting periods. 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 accommodate a variety of cell types and capacities from
multiple cell vendors. The I2C interface also allows read/write access to the Status, Configuration, and
Measurement Registers.
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DS2786 Standalone OCV-Based Fuel Gauge
Figure 3. Application Example
POWER MODES
The DS2786 operates in one of two power modes: Active and Sleep. While in Active mode, the DS2786 operates
as a high-precision battery monitor with temperature, voltage, auxiliary inputs, current, and accumulated current
measurements acquired continuously and the resulting values updated in the Measurement Registers. In Sleep
mode, the DS2786 operates in a low-power mode with no measurement activity. Read and write access is allowed
to all registers in either mode.
The DS2786 operating mode transitions from Sleep to Active when:
( SCL > VIH ) OR ( SDA > VIH )
The DS2786 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 DS2786
transitions from Sleep to Active mode when the battery is charged. If the bus is not pulled up, the DS2786 remains
in Sleep and cannot accumulate the charge current. This caution statement applies particularly to a battery that is
charged on a standalone charger.
PARAMETER MEASUREMENT
The DS2786 uses a Sigma Delta A/D converter to make measurements. The measurement sequence shown in
Figure 4 repeats continuously while the DS2786 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 DS2786 can be configured to measure
temperature using its on-chip sensor instead of the AIN1 input. When the internal temperature measurement uses
the AIN1 conversion timeslot, VOUT is not activated. A full sequence of voltage measurements nominally takes
1760ms to complete.
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DS2786 Standalone OCV-Based Fuel Gauge
Figure 4. Measurement Sequence
VOLTAGE MEASUREMENT
Battery voltage is measured at the VIN input with respect to VSS over a range of 0V to 4.999V and with a resolution
of 1.22mV. The result is updated every 880ms and placed in the Voltage Register in two’s compliment form.
Voltages above the maximum register value are reported as 7FFFh.
Figure 5. Voltage Register Format
MSB—Address 0Ch
211 210 29 28
LSB—Address 0Dh
22 21 20
S
27
26
25
24
23
X
X
X
MSb
LSb
MSb
LSb
Units: 1.22mV
“S”: sign bit(s), “X”: reserved
The input impedance of VIN is sufficiently large (>15MΩ) 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.
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DS2786 Standalone OCV-Based Fuel Gauge
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction to improve voltage
accuracy. Offset correction occurs approximately every 15 minutes. The resulting correction factor is applied to the
subsequent 1023 measurements. During the offset correction 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 DS2786 has two auxiliary voltage measurement inputs, AIN0 and AIN1. Both are measured with respect to
VSS. These inputs are designed for measuring resistor 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 outputs 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 calculations. 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. Auxiliary Input Registers Format
AIN0
MSB—Address 08h
210 29 28 27 26
LSB—Address 09h
21 20
S
25
24
23
22
X
X
X
X
MSb
LSb
MSb
LSb
Units: VOUT × 1/2047
“S”: sign bit, “X”: reserved
AIN1
MSB—Address 0Ah
210 29 28 27 26
LSB—Address 0Bh
21 20
S
25
24
23
22
X
X
X
X
MSb
LSb
MSb
LSb
Units: VOUT × 1/2047
“S”: sign bit, “X”: reserved
TEMPERATURE MEASUREMENT
The DS2786 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.
Figure 7. Temperature Register Format
MSB—Address 0Ah
28 27 26 25
LSB—Address 0Bh
20
S
29
24
23
22
21
X
X
X
X
X
MSb
LSb
MSb
LSb
Units: 0.125°C
“S”: sign bit(s), “X”: reserved
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DS2786 Standalone OCV-Based Fuel Gauge
CURRENT MEASUREMENT
In the Active mode of operation, the DS2786 continually measures the current flow into and out of the battery 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 values 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 completion of each conversion cycle. Figure 8 describes the Current Measurement Register format
and resolution for each option. 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).
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction to improve Current
accuracy. Offset correction occurs approximately every 15 minutes. The resulting correction factor is applied to the
subsequent 1023 measurements. During the offset correction conversion, the ADC does not make a measurement.
The current measurement just prior to the offset conversion is displayed in the Current Register.
Figure 8. Current Register Formats
MSB—Address 0Eh
210 29 28 27
LSB—Address 0Fh
21 20
S
26
25
24
23
22
X
X
X
X
MSb
LSb
MSb
LSb
“S”: sign bit
Units: 25μV/RSNS
Table 1. Current Range and Resolution for Various RSNS Values
CURRENT RESOLUTION (1 LSB)
RSNS
|VSS - VSNS
25µV
|
20mΩ
1.25mA
15mΩ
1.667mA
10mΩ
5mΩ
2.5mA
5mA
CURRENT INPUT RANGE
RSNS
VSS - VSNS
20mΩ
±2.56A
15mΩ
±3.41A
10mΩ
5mΩ
±51.2mV
±5.12A
±10.24A
CURRENT OFFSET BIAS
The Current Offset Bias Register (COBR) allows a programmable offset value to be added to raw current
measurements. The result of the raw current measurement 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
condition. The COBR value can be used to correct for a static 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
subsequent current measurements. COBR can be programmed 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.
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DS2786 Standalone OCV-Based Fuel Gauge
Figure 9. Current Offset Bias Register Format
Address 60h
S
26
25
24
23
22
21 20
LSb
25μV/RSNS
MSb
“S”: sign bit
Units:
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 measurement 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.
Table 2. Accumulated Current Range for Various RSNS Values
IACR RANGE
RSNS
VSS - VSNS
20mΩ
15mΩ
10mΩ
5mΩ
±204.8mVh
±10.24Ah
±13.65Ah
±20.48Ah
±40.96Ah
CELL CAPACITY ESTIMATION
The DS2786 uses a hybrid OCV measurement and coulomb counting algorithm to estimate remaining cell capacity.
During periods of charging or discharging of the cell, the DS2786 counts charge flow into and out of the cell. When
the application becomes inactive, the DS2786 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 percentage 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.
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DS2786 Standalone OCV-Based Fuel Gauge
Figure 10. Relative Capacity Register Format
Address 02h
24 23
27
26
25
22
21 20
LSb
MSb
Units: 0.5%
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 Relative Capacity (16h). After the first Learn operation, the
Relative 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 0.015Ω sense resistor would set the Initial Capacity Register to a
value of (100% ÷ (1Ah × 0.015Ω)) ÷ 78.125%/Vh = 55h. The Learned Capacity Scaling Factor Register is
controlled by the DS2786. The power up value is 00h, and the register is updated with the calculated new cell
capacity value after every Learn operation.
Figure 11. Initial Capacity Scaling Factor Register Format
Address 7Ah
27
26
25
24
23
22
21 20
LSb
MSb
Units: 78.125%/Vh
Figure 12. Learned Capacity Scaling Factor Register Format
Address 19h
27
26
25
24
23
22
21 20
LSb
MSb
Units: 78.125%/Vh
OCV DETECTION AND CURRENT BLANKING
The Blanking/OCV Threshold Register sets the current measurement level at which the DS2786 switches between
coulomb counting and open-circuit voltage measurement. When the magnitude of the measured current (after
COBR is applied) is less than the value defined by the Blanking/OCV Threshold Register, the measurement is not
summed into the IACR. Instead, the IACR is maintained at its present value and the DS2786 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 current of the application should be selected. The Blanking/OCV
Threshold Register has a resolution of 25μV/RSNS, and a range from 0mV/RSNS to 6.375mV/RSNS. The factory
default value is 06h
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DS2786 Standalone OCV-Based Fuel Gauge
Figure 13. Blanking/OCV Threshold Register Format
Address 7Bh
27
26
25
24
23
22
21 20
LSb
Units: 25μV/RSNS
MSb
While the measured current is below the Blanking/OCV Threshold level, the DS2786 actively searches for a
relaxed cell by calculating the change in cell voltage as reported in the Voltage Register over 15 minute intervals
(dV/dt). If the 15 minute dV/dt change of the Voltage Register is less than the value stored in the OCV dV/dt
Threshold Register, the DS2786 determines 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 will occur
repeatedly every 15 minutes until the DS2786 returns to coulomb-counting mode of operation.
The OCV dV/dt Threshold Register has a resolution of 1.22mV/15min and a range from 0mV/15min to
18.3mV/15min. The factory default value is 3.66mV/15min. 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. OCV dV/dt Threshold Register Format
Address 7Ch
23
22
21 20
LSb
SMOD VODIS LDIS ITEMP
MSb
Units: 1.22mV/15min
OCV CELL MODEL
The OCV cell model is a 9-point piece-wise linear approximation of open circuit cell voltage versus the remaining
capacity of the cell. Whenever an OCV update occurs, the Relative Capacity Register is adjusted 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.
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DS2786 Standalone OCV-Based Fuel Gauge
Figure 15. Default OCV Cell Model
4.2
Breakpoint 7
4.087V
90.5%
Breakpoint 4
3.831V
4
52.5%
Breakpoint 2
3.673V
Breakpoint 8
4.171V
10%
3.8
100%
Breakpoint 6
4.042
Breakpoint 5
4.005
3.6
Breakpoint 3
85%
80%
3.752
25%
Breakpoint 1
3.619V
5%
3.4
3.2
Breakpoint 0
3.186V
0%
3
100%
80%
60%
40%
20%
0%
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 otherwise can be written to any value between 0.5% to 99.5%. Capacity 8 is fixed at a value
of 100% and cannot be changed.
Voltage breakpoints required two bytes per breakpoint, but are otherwise stored in a similar manner. Voltage
Breakpoint 0: MSB stored at address 68h, LSB stored at address 69h. Other voltage breakpoints stored
sequentially through address location 79h. Each voltage breakpoint has a resolution of 1.22mV, and a range from
0.0V to 4.996V. Voltage breakpoint values must also be monotonic.
Figure 16. Capacity 1 to Capacity 7 Registers Format
Address 61h–67h
27
26
25
24
23
22
21 20
LSb
MSb
Units: 0.5%
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DS2786 Standalone OCV-Based Fuel Gauge
LSB—Odd Address 69h–79h
Figure 17. Voltage Breakpoint Register Format
MSB—Even Addresses 68h–78h
211 210 29
28
27
26
25
24
23
22
21
20
X
X
X
X
MSb
“X”: reserved
LSb
MSb
LSb
Units: 1.22mV
INITIAL CAPACITY ESTIMATION
The DS2786 calculates Relative Capacity immediately upon power up. During initialization, the DS2786 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 will be
removed at the next OCV adjustment. The initial voltage measurement used in determining the starting point is
stored in the Initial Voltage Register until the IC is power cycled.
Figure 18. Initial Voltage Register Format
MSB—Address 14h
211 210 29 28 27
LSB—Address 15h
23 22 21
20
X
X
X
S
26
25
24
MSb
LSb
MSb
LSb
Units: 1.22mV
“S”: sign bit(s), “X”: reserved
NEW CAPACITY LEARNING
As the cell ages, the Initial Capacity Scaling Factor Register value may no longer accurately reflect the true
capacity of the cell causing error in Relative Capacity calculation while in coulomb-counting mode of operation. The
DS2786 has a learn feature that allows the IC to remain accurate as the cell changes. The DS2786 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 percentage at the previous
OCV adjustment point used for learning the new cell capacity. Last OCV will be updated with a new value at each
OCV adjustment.
Example: Assuming a 15mΩ sense resistor, the DS2786 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 Scaling Factor value of
55h. The next OCV adjustment determines the Relative Capacity should actually be at 65%, not 60%. The DS2786
then adjusts the Learned Capacity Scaling Factor value upward to (65% - 10%) ÷ (500mAH × 0.015Ω) = 5Eh
lowering the expected cell capacity by approximately 10%.
Figure 19. Last OCV Register Format
Address 18h
27
26
25
24
23
22
21 20
LSb
MSb
Units: 0.5%
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DS2786 Standalone OCV-Based Fuel Gauge
The Learn Delta Percent Threshold allows the application to select how large of a cell capacity change is required
before the new cell capacity value is learned. The difference 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 recommended this
register be set to a value of at least 50%.
Figure 20. Learn Delta Percent Threshold
Address 17h
27
26
25
24
23
22
21 20
LSb
MSb
Units: 0.5%
MEMORY MAP
The DS2786 has memory space with registers for instrumentation, status, and control. When the MSB of a two-
byte register is read, both the MSB and LSB are latched and held for the duration of the read data command to
prevent updates during the read and ensure synchronization between the two register bytes. For consistent results,
always read the MSB and the LSB of a two-byte register during the same read data command sequence.
Memory locations 60h through 7Fh are EEPROM storage 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.
Setting the COPY bit of the Command 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 DS2786 requires the COPY
bit be reset to 0 within the tPROG time window to properly program EEPROM. Resetting COPY too soon may
prevent a proper write of the cells. Resetting COPY too late may degrade EEPROM Copy Endurance.
The DS2786 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 I.C. will cause the Shadow RAM data to be restored from EEPROM.
Figure 21. EEPROM Access via Shadow RAM
Copy
EEPROM
Write
Recall
Serial
Interface
Shadow RAM
Read
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DS2786 Standalone OCV-Based Fuel Gauge
Table 3. Memory Map
ADDRESS (HEX)
DESCRIPTION
READ/WRITE
00h
01h
Reserved
—
R/W
R
Status/Config Register
Relative Capacity
Reserved
02h
03h to 07h
08h
—
R
Auxiliary Input 0 MSB
Auxiliary Input 0 LSB
09h
R
0Ah
Auxiliary Input 1 / Temperature MSB
Auxiliary Input 1 / Temperature LSB
Voltage Register MSB
Voltage Register LSB
Current Register MSB
Current Register LSB
Reserved
R
R
0Bh
0Ch
R
0Dh
R
0Eh
R
0Fh
R
10h to 13h
14h
—
R
Initial Voltage MSB
Initial Voltage LSB
15h
R
16h
Last OCV Relative Capacity
Learned Capacity Scaling Factor
Reserved
R
17h
R
18h to 5Fh
60h to 7Fh
80h to FDh
FEh
—
R/W
—
R/W
—
Parameter EEPROM
Reserved
Command
FFh
Reserved
Table 4. Parameter EEPROM Memory Block
FACTORY
VALUE
FACTORY
VALUE
ADDRESS
DESCRIPTION
ADDRESS
DESCRIPTION
60h
61h
62h
63h
64h
65h
66h
67h
68h
69h
6Ah
6Bh
6Ch
6Dh
6Eh
6Fh
Current Offset Bias Register
Capacity 1
00h
70h
71h
72h
73h
74h
75h
76h
77h
78h
79h
7Ah
7Bh
7Ch
7Dh
7Eh
7Fh
Voltage Breakpoint 4 MSB
Voltage Breakpoint 4 LSB
Voltage Breakpoint 5 MSB
Voltage Breakpoint 5 LSB
Voltage Breakpoint 6 MSB
Voltage Breakpoint 6 LSB
Voltage Breakpoint 7 MSB
Voltage Breakpoint 7 LSB
Voltage Breakpoint 8 MSB
Voltage Breakpoint 8 LSB
Initial Capacity Scaling Factor
Blanking/OCV Current Threshold
OCV dV/dt Threshold
C4h
20h
CDh
10h
CEh
F0h
D1h
40h
D5h
90h
80h
06h
93h
60h
78h
00h
0Ah
14h
32h
69h
A0h
AAh
B5h
A3h
20h
B9h
50h
BCh
10h
C0h
20h
Capacity 2
Capacity 3
Capacity 4
Capacity 5
Capacity 6
Capacity 7
Voltage Breakpoint 0 MSB
Voltage Breakpoint 0 LSB
Voltage Breakpoint 1 MSB
Voltage Breakpoint 1 LSB
Voltage Breakpoint 2 MSB
Voltage Breakpoint 2 LSB
Voltage Breakpoint 3 MSB
Voltage Breakpoint 3 LSB
I2C Address
Learn Threshold
User EEPROM
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DS2786 Standalone OCV-Based Fuel Gauge
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.
Figure 22. Status/Config Register Format
ADDRESS 01h
BIT 7
X
BIT 6
BIT 5
BIT 4
LDIS
BIT 3
BIT 2
BIT 1
AIN1
BIT 0
AIN0
PORF
SMOD
VODIS
ITEMP
X—Reserved.
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 0 in order to use it to indicate subsequent power-up events. POR event will cause a reset
of the fuel gauge. PORF is read/write-to-zero.
SMOD—Sleep Mode Enable. A value of 1 allows the DS2786 to enter Sleep mode when SCL AND SDA are low
for tSLEEP. A value of 0 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 DS2786
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 DS2786. A value of 0 allows cell
capacity learning to occur normally. This bit is EEPROM backed by bit 5 of memory location 7Ch. The factory
programmed value is 0.
VODIS—VOUT Disable. A value of 1 disables the VOUT output. When set to 0 this output is driven tPRE before the
AIN0 conversion begins, and disabled after the AIN1 conversion ends. This bit is EEPROM backed by bit 6 of
memory location 7Ch. The factory-programmed value is 0.
ITEMP—ITEMP. A value of 1 enables measurement of temperature using the internal sensor during the AIN1
conversion timeslot. AIN1 input is not selected and VOUT is not enabled during the AIN1 timeslot. A value of 0
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.
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DS2786 Standalone OCV-Based Fuel Gauge
COMMAND REGISTER
The Command Register is read/write accessible. Bit values indicate operations requested to be performed by the
device.
Figure 23. Command Register Format
ADDRESS FEh
BIT 7
POR
BIT 6
X
BIT 5
X
BIT 4
X
BIT 3
BIT 2
BIT 1
BIT 0
POCV
SOCV
RCALL
COPY
X—Reserved.
COPY—The Copy bit is set to start a copy command of the scratch pad to EEPROM. A programming voltage 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 scratch pad.
SOCV—Stored OCV Calculation. This command may be used to reset the Relative Capacity calculation after
updating OCV cell model data in the Scratchpad. When set to one 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 scratch pad.
Writing the bit to 1 forces a calculation. Forcing an OCV calculation will create capacity estimation error. The bit is
cleared when the hardware completes the calculation.
POCV—Present OCV Calculation. When set to one 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 scratch pad. Writing the bit to 1
forces a calculation. This function should be used for test purposes only. Forcing an OCV calculation will create
capacity estimation error. The bit is cleared when the hardware completes 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 one 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
multimaster 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 DS2786 slave device and a master device at speeds up to
400kHz. The DS2786’s SDA pin operates bidirectionally, that is, when the DS2786 receives data, SDA operates as
an input, and when the DS2786 returns data, SDA operates as an open-drain output, with the host system
providing a resistive pullup. The DS2786 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 interpreted as a START or STOP control signal.
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DS2786 Standalone OCV-Based Fuel Gauge
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 condition (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 systems, 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 DS2786 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 generate a No Acknowledge (also called NAK), the receiver releases SDA before the rising edge of
the acknowledge-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 re-
attempt communication.
Data Order
A byte of data consists of 8 bits ordered most significant bit (MSB) first. The least significant bit (LSB) of each byte
is followed by the Acknowledge bit. DS2786 registers composed of multibyte values are ordered most significant
byte (MSB) first. The MSB of multibyte registers is stored on even data memory addresses.
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 DS2786 continuously monitors for a
START condition followed by its slave address. When the DS2786 receives a slave address that matches its Slave
Address, it responds with an Acknowledge bit during the clock period following the R/W bit. 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 Register at location 7Dh.
Figure 24. I2C Address Register Format
ADDRESS 7Dh
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
X
BIT 2
X
BIT 1
X
BIT 0
X
ADDR3 ADDR2 ADDR1 ADDR0
X—Reserved.
ADDR3:0—User-adjustable bits of the DS2786’s I2C address. Factory default is 0110.
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DS2786 Standalone OCV-Based Fuel Gauge
Figure 25. DS2786 I2C Address Byte Format
BIT 7
0
BIT 6
1
BIT 5
1
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
ADDR3 ADDR2 ADDR1 ADDR0
R/W
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.
Bus Timing
The DS2786 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 formats. The simplest format consists of the master writing the
START bit, slave address, R/W bit, and then monitoring the acknowledge bit for presence of the DS2786. More
complex formats such as the Write Data, Read Data, and Function command protocols write data, read data, and
execute device specific operations. All bytes in each command format require the slave or host to return an
Acknowledge bit before continuing with the next byte. Each function command definition outlines the required
transaction format. The following key applies to the transaction formats.
Table 5. 2-Wire Protocol Key
KEY
S
DESCRIPTION
START bit
KEY
Sr
DESCRIPTION
Repeated START
SAddr Slave Address (7-bit)
FCmd Function Command byte
MAddr Memory Address byte
W
R
P
R/W bit = 0
R/W bit = 1
STOP bit
Data
A
N
Data byte written by master
Acknowledge bit—Master
No AcknowledgeMaster
Data
A
N
Data byte returned by slave
Acknowledge bit—Slave
No Acknowledge—Slave
Basic Transaction Formats
Write: S SAddr W A MAddr A Data0 A P
A write transaction transfers one or more data bytes to the DS2786. 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 transaction,
except for the Acknowledge cycles.
Read:
S SAddr W A MAddr A Sr SAddr R A Data0 N P
Write Portion
Read Portion
A read transaction transfers one or more bytes from the DS2786. Read transactions are composed of two parts, a
write portion followed by a read portion, and is therefore inherently longer than a write transaction. The write portion
communicates the starting point for the read operation. The read portion follows immediately, beginning with a
Repeated START, Slave Address with R/W set to a 1. Control of SDA is assumed by the DS2786 beginning with
the Slave Address Acknowledge cycle. Control of the SDA signal is retained by the DS2786 throughout the
transaction, except for the Acknowledge cycles. The master indicates the end of a read transaction by responding
to the last byte it requires with a No Acknowledge. This signals the DS2786 that control of SDA is to remain with
the master following the Acknowledge clock.
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DS2786 Standalone OCV-Based Fuel Gauge
Write Data Protocol
The write data protocol is used to write to register and shadow RAM data to the DS2786 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 least significant bit (LSB) of each byte
is received by the DS2786, the MSB of the data at address MAddr + 1 is can be written immediately after the
acknowledgement of the data at address MAddr. If the bus master continues an auto-incremented write transaction
beyond address 4Fh, the DS2786 ignores the data. Data is also ignored on writes to read-only addresses and
reserved addresses, as well as a write that auto increments to the Function Command Register (address FEh).
Incomplete bytes and bytes that are Not Acknowledged by the DS2786 are not written to memory. As noted in the
Memory 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 DS2786 starting at memory
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 A … DataN N P
Data is returned beginning with the MSB of the data in MAddr. Because the address is automatically incremented
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 acknowledgement of the data at address MAddr. If the bus master continues to read beyond
address FFh, the DS2786 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
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package
outline information, go to www.maxim-ic.com/DallasPackInfo.)
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