DS2786BG+T&R - Hytronics

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

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

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

tLOW

tHD:STA

tHD:DAT

tSU:STA tSU:STO

tSU:DAT tHD:STA

tSP tRtBUF

SSr

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.

VDD

VOUT

VPROG

AIN1

SCL

SDA

VIN

AIN0

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

GROUND

VDD

VSS

BIAS

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

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

0.86ms

DELAY

0.86ms

DELAY

0.86ms

DELAY

0.86ms

DELAY

tPRE

VOLTAGE

VOUT PIN

ALTERNATING AIN0 OR

AIN1/TEMPERATURE

MEASUREMENT

AIN0 OR AIN1/

TEMPERATURE REGISTER

DIFFERENTIAL

CURRENT

MEASUREMENT

CURRENT

CYCLE OF MEASUREMENTS REPEATS EVERY 880ms.

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

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|20m15m 10m5m

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

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

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

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

cell. For example, an application using a 1Ah cell and

0.015Ωsense resistor would set the Initial Capacity

78.125%/Vh = 55h. The Learned Capacity Scaling Factor

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

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

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

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

MSB LSB

UNITS: 25μV/RSNS

Figure 13. OCV Threshold Register Format

ADDRESS 7Ch

SMOD LDIS VODIS ITEMP 23 2

2 2

1 2

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

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

BREAKPOINT 0

3.186V

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

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

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

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

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

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

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 ____________________

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