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DS2786G+-DS2786G+T&R
Stand-Alone OCV-Based Fuel Gauge
GENERAL DESCRIPTION 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.
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.
APPLICATIONS 3G Multimedia Wireless Handsets
Digital Still Cameras
Digital Audio (MP3) Players
TYPICAL OPERATING CIRCUIT
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: 25V LSB, ±51.2mV Dynamic Range
1.67mA LSB, ±3.4A (RSNS = 15m)
Current Accumulation Measurement
Resolution: ±204.8mVh Range
±13.65Ah (RSNS = 15m)
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
Low Power Consumption: Active Current: 50A typ, 80A max
Sleep Current: 1A typ, 3A max
ORDERING INFORMATION
PART TEMP RANGE PIN-PACKAGE DS2786G+ -20ºC to +70ºC 10 TDFN-EP*
DS2786G+T&R -20ºC to +70ºC 10 TDFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
*EP = Exposed pad.
PIN CONFIGURATION 3mm x 3mm TDFN-10
DS2786
Stand-Alone OCV-Based
Fuel Gauge
19-4637; 5/09
DS2786 Stand-Alone OCV-Based Fuel Gauge
ABSOLUTE MAXIMUM RATINGS Voltage Range on All Pins Except VPROG Relative to VSS -0.3V to +6V
Voltage Range 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
Soldering Temperature Refer to the IPC/JEDECJ-STD-020 Specification.
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 4.5V, TA = -20C to +70C.)
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
DC ELECTRICAL CHARACTERISTICS (2.5V VDD 4.5V, TA = -20C to +70C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Active Current IACTIVE 50 75 A
VDD = 2.0V,
SCL, SDA = VSS 0.3 1.0
Sleep-Mode Current ISLEEP
SCL, SDA = VSS 1 3 A
Current Measurement
Resolution ILSB DS2786 25 V
Current Measurement
Full-Scale Magnitude IFS (Note 1) ±51.2 mV
Current Measurement
Offset Error IOERR DS2786 (Note 2) -50 +50 V
Current Measurement
Gain Error IGERR -1.5 +1.5 % of
reading
VDD = 3.6V at +25°C -1 +1
TA = 0C to +70C -2 +2 Timebase Accuracy tERR
TA = -20C to +70C -3 +3
VDD = VIN = 3.6V,
TA = 0C to +50C -10 +10
Voltage Error VGERR
TA = -20C to +70C -20 +20
mV
Input Resistance
VIN, AIN0, AIN1 RIN 15 MΩ
AIN0, AIN1 Error -8 +8 LSB
DS2786 Stand-Alone OCV-Based Fuel Gauge
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS VOUT Precharge Time tPRE 13.2 13.7 14.2 ms
Temperature Error TERR -3 +3 °C
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 VDD = 4.2V,
VPIN = 0.4V 0.2 1.0 A
VPROG Pulldown RVPROG 20 kΩ
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
ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (2.5V VDD 4.5V, TA = -20C to +70C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS SCL Clock Frequency fSCL (Note 4) 0 400 kHz
Bus Free Time Between
a STOP and START
Condition BUF 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 SU: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 tR 20 + 0.1CB 300 ns
Fall Time of Both SDA
and SCL Signals tF 20 + 0.1CB 300 ns
Setup Time for STOP
DS2786 Stand-Alone OCV-Based Fuel Gauge
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Spike Pulse Widths
Suppressed by Input
Filter SP (Note 8) 0 50 ns
Capacitive Load for Each
Bus Line CB (Note 9) 400 pF
SCL, SDA Input
Capacitance CBIN 60 pF
Note 1: All voltages are referenced to VSS.
Note 2: Offset specified after auto-calibration cycle and Current Offset Bias Register = 00h.
Note 3: The DS2786 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 DS2786 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.
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.
Figure 1. 2-Wire Bus Timing Diagram DS2786 Stand-Alone OCV-Based Fuel Gauge
PIN DESCRIPTION
PIN NAME FUNCTION 1 AIN1
Aux Voltage Input Number 1 2 AIN0
Aux 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 Aux 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.
PAD PAD
Exposed Pad. Connect to VSS.
Figure 2. Block Diagram VIN
DS2786 Stand-Alone OCV-Based Fuel Gauge
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 15m 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.
Figure 3. Application Example DS2786 Stand-Alone OCV-Based Fuel Gauge
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 stand-alone 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.
Figure 4. Measurement Sequence
DS2786 Stand-Alone OCV-Based Fuel Gauge
VOLTAGE MEASUREMENT Battery voltage is measured at the VIN input with respect to VSS over a range of 0V to 4.5V 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. Voltage Register Format MSB—Address 0Ch LSB—Address 0Dh
S 211 210 29 28 27 26 25 24 23 22 21 20 X X X
MSb LSb MSb LSb
“S”: sign bit(s), “X”: reserved Units: 1.22mV
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.
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 LSB—Address 09h
S 210 29 28 27 26 25 24 23 22 21 20 X X X X
MSb LSb MSb LSb
“S”: sign bit, “X”: reserved Units: VOUT × 1/2047
AIN1 MSB—Address 0Ah LSB—Address 0Bh
S 210 29 28 27 26 25 24 23 22 21 20 X X X X
MSb LSb MSb LSb
“S”: sign bit, “X”: reserved Units: VOUT × 1/2047
DS2786 Stand-Alone OCV-Based Fuel Gauge
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 LSB—Address 0Bh
S 29 28 27 26 25 24 23 22 21 20 X X X X X
MSb LSb MSb LSb
“S”: sign bit(s), “X”: reserved Units: 0.125C
CURRENT MEASUREMENT In the Active mode of operation, the 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 LSB—Address 0Fh
S 210 29 28 27 26 25 24 23 22 21 20 X X X X
MSb LSb MSb LSb
“S”: sign bit Units: 25V/RSNS
DS2786 Stand-Alone OCV-Based Fuel Gauge
Table 1. Current Range and Resolution for Various RSNS Values
CURRENT RESOLUTION (1 LSB) RSNS |VSS - VSNS|
20m 15m 10m 5m
25V 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
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 25V 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. Current Offset Bias Register Format Address 60h
S 26 25 24 23 22 21 20 MSb LSb“S”: sign bit Units: 25V/RSNS
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 20m 15m 10m 5m
±204.8mVh ±10.24Ah ±13.65Ah ±20.48Ah ±40.96Ah
DS2786 Stand-Alone OCV-Based Fuel Gauge
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.
Figure 10. Relative Capacity Register Format Address 02h 7 26 25 24 23 22 21 20 MSb LSb
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 0.015 sense resistor would set the Initial Capacity Register to a
value of (100% ÷ (1Ah × 0.015)) ÷ 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 7 26 25 24 23 22 21 20 MSb LSb
Units: 78.125%/Vh
Figure 12. Learned Capacity Scaling Factor Register Format Address 17h 7 26 25 24 23 22 21 20 MSb LSb
Units: 78.125%/Vh
