MAXIM DS2782 Technical data

Standalone Fuel Gauge IC

DS2782

www.maxim-ic.com

GENERAL DESCRIPTION

The DS2782 measures voltage, temperature and
current, and estimates available capacity for
rechargeable lithium ion and lithium-ion polymer
batteries. Cell characteristics and application
parameters used in the calculations are stored in on­chip EEPROM. The available capacity registers
report a conservative estimate of the amount of
charge that can be removed given the current
temperature, discharge rate, stored charge and
application parameters. Capacity estimation reported
in mAh remaining and percentage of full.

PIN CONFIGURATION

APPLICATIONS

Digital Still Cameras

Sub-Notebook Computers

Handheld PC Data Terminals

3G Multimedia Wireless Handsets

TYPICAL OPERATING CIRCUIT

FEATURES

 Precision Voltage, Temperature, and Current

Measurement System

 Accurate Stable Internal Time Base
 Absolute and Relative Capacity Estimated from

Coulomb Count, Discharge Rate, Temperature
and Battery Cell Characteristics

 Accurate Warning of Low Battery Conditions
 Automatic Backup of Coulomb Count and Age

Estimation to Nonvolatile (NV) EEPROM

 Gain and Tempco Calibration Allows the Use of

Low-Cost Sense Resistors

 24-Byte User EEPROM or 16-Byte User

EEPROM and Unique 64-bit ID

 Industry 2-Wire Interface with Programmable

Slave Address

 Tiny TSSOP-8 and TDFN-10 Packages Embed

Easily in Thin Prismatic Cell packs

ORDERING INFORMATION

PART MARKING PACKAGE INFORMATION

DS2782E+ 2782+ Lead-Free TSSOP-8
DS2782E+T&R 2782+ DS2782E+, Tape-and-Reel
DS2782G+ 2782+ Lead-Free 3mm x 4mm TDFN-10
DS2782G+T&R 2782+ DS2782G+, Tape-and-Reel

Note: To order devices with the unique 64-bit ID option, contact Maxim/Dallas Semiconductor sales.

Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata

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.

050907

DS2782: Standalone Fuel Gauge IC

ABSOLUTE MAXIMUM RATINGS

Voltage Range on Any Pin Relative to V
Voltage on V

Relative to VSS -0.3V to VDD+0.3

IN

Operating Temperature Range -40°C to +85°C
Storage Temperature Range
Soldering Temperature

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 the absolute maximum rating conditions for extended periods may affect device.

-55°C to +125°C

See IPC/JEDEC J-STD-020 Specification

-0.3V to +6.0V

SS

RECOMMENDED DC OPERATING CHARACTERISTICS

(VDD = 2.5V to 5.5V; TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VDD (Note 1) +2.5 +5.5 V
SDA, SCL, PIO Voltage
Range

DC ELECTRICAL CHARACTERISTICS

(VDD = 2.5V to 5.5V; TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

(Note 1) -0.3 +5.5 V

ACTIVE Current I

SLEEP Mode Current I

Input Logic High:
SDA, SCL, PIO
Input Logic Low:
SDA, SCL, PIO

ACTIVE

SLEEP

V

IH

V

IL

2.5V ≤ VDD ≤ 4.2V 65 95
µA

105

2.5V ≤ VDD ≤ 4.2V 1 3 µA

(Note 1) 1.5 V

(Note 1) 0.6 V

Output Logic Low: SDA, PIO VOL IOL = 4mA (Note 1) 0.4 V
Pulldown Current:

SDA, SCL, PIO

I

PD

VIN Input Resistance RIN 15

Bus Low to Sleep time

Undervoltage SLEEP
Threshold

t

SLEEP

V

SLEEP

V

, V

, V

SDA

0.4V

SCL

PIO

=

0.2 µA

MΩ
SDA, SCL < V
(Note 2)

IL

2.2 s

(Note 1) 2.40 2.45 2.50 V

ELECTRICAL CHARACTERISTICS: TEMPERATURE, VOLTAGE, CURRENT

(VCC = 2.5V to 5.5V; TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Temperature Resolution T

Temperature Error T

Voltage Resolution V

Voltage Full-Scale VFS 0 4.992 V

0.125 °C

LSB

±3 °C

ERR

4.88 mV

LSB

Voltage Error V

Current Resolution I

±50 mV

ERR

1.56 µV

LSB

Current Full-Scale IFS ±51.2 mV

2 of 25

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Current Gain Error I

Current Offset Error I

(Note 3) ±1

GERR

≤ +70°C,

A

≤ 4.2V

DD

OERR

0°C ≤ T

2.5V ≤ V
(Note 5)

≤ +70°C,

A

≤ 4.2V

DD

= VSS, (Notes 4, 5)

Accumulated Current Offset q

OERR

0°C ≤ T

2.5V ≤ V
V

SNS

VDD = 3.8V, TA = +25°C ±1

Timebase Error t

ERR

0°C ≤ TA ≤ +70°C,

2.5V ≤ VDD ≤ 4.2V

±3

ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE

(2.5V ≤ VDD ≤ 5.5V, TA = -20°C to +70°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DS2782: Standalone Fuel Gauge IC

% Full-

Scale

- 7.82 + 12.5 µV

- 188 + 0

±2

µVhr/

day

%

SCL Clock Frequency

Bus Free Time Between a STOP
and START Condition

Hold Time (Repeated)
START Condition

Low Period of SCL Clock

High Period of SCL Clock

Setup Time for a Repeated
START Condition

Data Hold Time

Data Setup Time

Rise Time of Both SDA and
SCL Signals

Fall Time of Both SDA and
SCL Signals

Setup Time for STOP
Condition

Spike Pulse Widths Suppressed
by Input Filter

Capacitive Load for Each Bus
Line

SCL, SDA Input Capacitance C

f

(Note 6) 0 400 KHz

SCL

t

1.3 µs

BUF

t

HD:STA

t

LOW

t

HIGH

t

SU:STA

t

HD:DAT

t

SU:DAT

t

R

t

F

t

SU:STO

t

SP

C

(Note 11) 400 pF

B

BIN

(Note 7) 0.6 µs

1.3 µs

0.6 µs

0.6 µs

(Note 8, 9) 0 0.9 µs

(Note 8) 100 ns

20 + 0.1C

20 + 0.1C

0.6 µs

(Note 10) 0 50 ns

300 ns

B

300 ns

B

60 pF

EEPROM RELIABILITY SPECIFICATION

(VCC = 2.5V to 5.5V; TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

EEPROM Copy Time t

EEPROM Copy Endurance N

10 ms

EEC

TA = +50°C 50,000 cycles

EEC

3 of 25

DS2782: Standalone Fuel Gauge IC

Note 1: All voltages are referenced to V
Note 2: To properly enter sleep mode the application should hold the bus low for longer than the maximum t

SS

.

SLEEP

Note 3: Factory calibrated accuracy. Higher accuracy can be achieved by in-system calibration by the user.
Note 4: Accumulation bias register set to 00h.
Note 5: Parameters guaranteed by design.
Note 6: Timing must be fast enough to prevent the DS2782 from entering sleep mode due to bus low for period >

t

SLEEP.

Note 7: f
Note 8: The maximum t

must meet the minimum clock low time plus the rise/fall times.

SCL

has only to be met if the device does not stretch the LOW period (t

HD:DAT

) of the SCL

LOW

signal.

Note 9: This device internally provides a hold time of at least 300 ns for the SDA signal (referred to the VIHmin of

the SCL signal) to bridge the undefined region of the falling edge of SCL.

Note 10: Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant.
Note 11: C

– total capacitance of one bus line in pF.

b

Figure 1. I2C Bus Timing Diagram

.

4 of 25

DS2782: Standalone Fuel Gauge IC

PIN DESCRIPTION

NAME

TSSOP

PIN

NC 1 1 Not Connected. Pin not connected internally, float or connect to VSS.

VSS 2 2, 3

VIN 3 4

VDD 4 5

SDA 5 6

SCL 6 7

N.C. — 8 No Connection. (Only present on TDFN package).

TDFN

PIN

FUNCTION

Device Ground. Connect directly to the negative terminal of the battery cell.

Connect the sense resistor between VSS and SNS.

Voltage Sense Input. The voltage of the battery cell is monitored through this

input pin.

Power-Supply Input. Connect to the positive terminal of the battery cell through a

decoupling network.

Serial Data Input/Out. 2-Wire data line. Open-drain output driver. Connect this pin

to the DATA terminal of the battery pack. Pin has an internal pull-down (IPD) for
sensing disconnection.

Serial Clock Input. 2-Wire clock line. Input only. Connect this pin to the CLOCK

terminal of the battery pack. Pin has an internal pull-down (I

) for sensing

PD

disconnection.

SNS 7 9

PIO 8 10

PAD — PAD

Sense Resistor Connection. Connect to the negative terminal of the battery

pack. Connect the sense resistor between VSS and SNS.

Programmable I/O Pin. Can be configured as input or output to monitor or control

user-defined external circuitry. Output driver is open drain. This pin has a weak
internal pulldown (I

PD

).

Exposed Pad. Connect to VSS or leave floating. (Only present on TDFN

package).

5 of 25

Figure 2. Block Diagram

VDD

EN

VPOR

PIO

SDA

SCL

2-Wire

Interface

BIAS/VREF Timebase

Status

&

Control

DS2782: Standalone Fuel Gauge IC

VIN

Temp

&

Voltage

ADC

EEPROM

Accumulated

Current

SNS VSS

Current ADC

Rate,

Temperature

Compensation

15 bit + sign

DETAILED DESCRIPTION

The DS2782 operates directly from 2.5V to 5.5V and supports single cell Lithium-ion battery packs. As shown in
Figure 3, the DS2782 accommodates multicell applications by adding a voltage regulator for VDD and voltage
divider for VIN. Nonvolatile storage is provided for cell compensation and application parameters. Host side
development of fuel-gauging algorithms is eliminated. On-chip algorithms and convenient status reporting of
operating conditions reduce the serial polling required of the host processor.

Additionally, 16 bytes of EEPROM memory are made available for the exclusive use of the host system and/or
pack manufacturer. The additional EEPROM memory can be used to facilitate battery lot and date tracking and NV
storage of system or battery usage statistics.

Through its 2-Wire interface, the DS2782 gives the host system read/write access to status and control registers,
instrumentation registers, and general-purpose data storage. The 7-bit slave address is field programmable, thus
allowing up to 128 devices to be distinctly addressed by the host system. A unique, factory programmed 64-bit
registration number (8-bit family code + 48-bit serial number + 8-bit CRC) option assures that no two parts are alike
and enables absolute traceability.

6 of 25

Figure 3. Multicell Application Example

Pack+

DS2782: Standalone Fuel Gauge IC

4.7uF0.1uF

SDA

150

SDA

VDD

500

(n * R)

Multi-Cell

Li-Ion

Battery

SCL

Pack-

150

(1) (1)

Protection

Circuit

(1) Components improve IEC1004 Air/Contact ESD compliance

SCL

PIO

SNS

RSNS

VIN

NC

VSS

R

0.1uF

POWER MODES

The DS2782 has two power modes: ACTIVE and SLEEP. On initial power up, the DS2782 defaults to ACTIVE
mode. While in ACTIVE mode, the DS2782 is fully functional with measurements and capacity estimation
continuously updated. In SLEEP mode, the DS2782 conserves power by disabling measurement and capacity
estimation functions, but preserves register contents. SLEEP mode is entered under two different conditions and
an enable bit for each condition makes entry into SLEEP optional. SLEEP mode can be enabled using the Power
Mode (PMOD) bit or the Under Voltage Enable (UVEN) bit.

The PMOD type SLEEP is entered if the PMOD bit is set AND
where both SDA AND
in which the bus pull-up voltage, V

SCL low for tSLEEP (2s nominal), is used to detect a pack disconnection or system shutdown

, is not present. PMOD SLEEP assumes that no charge or discharge

PULLUP

a bus low condition occurs. A bus low condition,

current will flow and therefore coulomb counting is not necessary. A system with PMOD SLEEP enabled must
ensure that a standalone or cradle charger includes a pull-up on SDA and/or SCL. The DS2782 transitions from
PMOD SLEEP to ACTIVE mode when either SDA or SCL is pulled high.

The second option for entering SLEEP is an under voltage condition measured on VIN. When the UVEN bit is set,
the DS2782 will transition to SLEEP if the voltage on VIN is less than V
is in a bus high or a bus low condition for t

SLEEP. UVEN SLEEP relieves the battery of the DS2782 load until

SLEEP (2.45V nominal) AND the 2-Wire bus

communication resumes to prevent over discharging the battery. The DS2782 transitions from UVEN SLEEP to
ACTIVE mode when either SDA or SCL change logic state. The bus master should initiate a transaction after
charging of a depleted battery begins.

Note: PMOD and UVEN SLEEP features must be disabled when a battery is charged on an external charger that
does not connect to SDA and/or SCL. PMOD SLEEP can be used if the charger pulls the bus high. The DS2782
remains in SLEEP and therefore does not measure or accumulate current when a battery is charged on a charger
that fails to properly drive the communication bus.

7 of 25

DS2782: Standalone Fuel Gauge IC

INITIATING COMMUNICATION IN SLEEP

When beginning communication with a DS2782 in PMOD SLEEP, the bus must be pulled up before a START bit
can be issued by the master. In UVEN SLEEP, the procedure depends on the bus state when UVEN SLEEP was
entered. If the bus was low, it must be pulled up before a START bit can be issued by the master as required with
PMOD SLEEP. If the bus was high when UVEN SLEEP was entered, then the DS2782 is prepared to receive a
START bit from the master. A standard procedure of issuing a START – STOP – START when the host system is
powered up on the charger input properly initiates communication from both PMOD and UVEN SLEEP modes.

VOLTAGE MEASUREMENT

Battery voltage is measured at the VIN input with respect to VSS over a range of 0V to 4.992V, with a resolution of

4.88mV. The result is updated every 440ms and placed in the VOLTAGE register in two’s compliment form.
Voltages above the maximum register value are reported at the maximum value; voltages below the minimum
register value are reported at the minimum value. The format of the voltage register is shown in Figure 4.

Figure 4. Voltage Register Format

VOLT

MSB—Address 0Ch LSB—Address 0Dh

9

S 2

MSb LSb MSb LSb

“S”: sign bit(s), “X”: reserved

VIN is usually connected to the positive terminal of a single cell Lithium-Ion battery via a 1kΩ resistor. The input
impedance 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. In Figure 3, the value of R can be up to 1MΩ without incurring significant error
due to input loading.

28 27 26 25 24 23 22 21 20 X X X X X

Read Only

Units: 4.88mV

TEMPERATURE MEASUREMENT

The DS2782 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C.
Temperature measurements are updated every 440ms and placed in the temperature register in two’s complement
form. The format of the temperature register is shown in Figure 5.

Figure 5. Temperature Register Format

TEMP

MSB—Address 0Ah LSB—Address 0Bh

9

S 2

MSb LSb MSb LSb

“S”: sign bit(s), “X”: reserved

28 27 26 25 24 23 22 21 20 X X X X X

Read Only

Units: 0.125°C

8 of 25

DS2782: Standalone Fuel Gauge IC

CURRENT MEASUREMENT

In the ACTIVE mode of operation, the DS2782 continually measures the current flow into and out of the battery by
measuring the voltage drop across a low-value current-sense resistor, R
SNS and VSS is ±51.2mV. The input linearly converts peak signal amplitudes up to 102.4mV as long as the
continuous signal level (average over the conversion cycle period) does not exceed ±51.2mV. The ADC samples
the input differentially at 18.6kHz and updates the Current register at the completion of each conversion cycle.

The Current register is updated every 3.515s with the current conversion result in two’s complement form. 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).

. The voltage-sense range between

SNS

Figure 6. Current Register Format

CURRENT

S 2

MSb LSb MSb LSb

“S”: sign bit(s)

MSB—Address 0Eh LSB—Address 0Fh

14

213 212 211 210 29 28 27 26 25 24 23 22 21 20

Units: 1.5625μV/Rsns

Read Only

CURRENT RESOLUTION (1 LSB)

R

VSS -

VSNS

1.5625μV 78.13μA 104.2μA 156.3μA 312.5μA

20mΩ 15mΩ 10mΩ 5mΩ

SNS

AVERAGE CURRENT MEASUREMENT

The Average Current register reports an average current level over the preceding 28 seconds. The register value is
updated every 28s in two’s complement form, and is the average of the 8 preceding Current register updates. The
format of the Average Current register is shown in Figure 7. 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).

Figure 7. Average Current Register Format

IAVG

S 2

MSb LSb MSb LSb

“S”: sign bit(s)

MSB—Address 08h LSB—Address 09h

14

213 212 211 210 29 28 27 26 25 24 23 22 21 20

Units: 1.5625μV/Rsns

R/W

CURRENT OFFSET CORRECTION

Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs
approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements.
During the offset correction conversion, the ADC does not measure the sense resistor signal. A maximum error of
1/1024 in the accumulated current register (ACR) is possible; however, to reduce the error, the current
measurement made just prior to the offset conversion is displayed in the current register and is substituted for the
dropped current measurement in the current accumulation process. This results in an accumulated current error
due to offset correction of less than 1/1024.

9 of 25

DS2782: Standalone Fuel Gauge IC

CURRENT MEASUREMENT CALIBRATION

The DS2782’s current measurement gain can be adjusted through the RSGAIN register, which is factory-calibrated

to meet the data sheet specified accuracy. RSGAIN is user accessible and can be reprogrammed after module or
pack manufacture to improve the current measurement accuracy. Adjusting RSGAIN can correct for variation in an
external sense resistor’s nominal value, and allows the use of low-cost, non-precision current sense resistors.
RSGAIN is an 11 bit value stored in 2 bytes of the Parameter EEPROM Memory Block. The RSGAIN value adjusts
the gain from 0 to 1.999 in steps of 0.001 (precisely 2
accurate current measurement. When shipped from the factory, the gain calibration value is stored in two separate
locations in the Parameter EEPROM Block, RSGAIN which is reprogrammable and FRSGAIN which is read only.
RSGAIN determines the gain used in the current measurement. The read-only FRSGAIN is provided to preserve
the factory value only and is not used in the current measurement.

-10

). The user must program RSGAIN cautiously to ensure

SENSE RESISTOR TEMPERATURE COMPENSATION

The DS2782 is capable of temperature compensating the current sense resistor to correct for variation in a sense
resistor’s value over temperature. The DS2782 is factory programmed with the sense resistor temperature
coefficient, RSTC, set to zero, which turns off the temperature compensation function. RSTC is user accessible
and can be reprogrammed after module or pack manufacture to improve the current accuracy when using a high
temperature coefficient current-sense resistor. RSTC is an 8-bit value stored in the Parameter EEPROM Memory
Block. The RSTC value sets the temperature coefficient from 0 to +7782ppm/ºC in steps of 30.5ppm/ºC. The user
must program RSTC cautiously to ensure accurate current measurement.

Temperature compensation adjustments are made when the Temperature register crosses 0.5
temperature compensation is most effective with the resistor placed as close as possible to the VSS terminal to
optimize thermal coupling of the resistor to the on-chip temperature sensor. If the current shunt is constructed with
a copper PCB trace, run the trace under the DS2782 package if possible.

o

C boundaries. The

CURRENT ACCUMULATION

Current measurements are internally summed, or accumulated, at the completion of each conversion period with
the results displayed in the Accumulated Current Register (ACR). The accuracy of the ACR is dependent on both
the current measurement and the conversion timebase. The ACR has a range of 0 to 409.6mVh with an LSb of

6.25μVh. Additional read-only registers (ACRL) hold fractional results of each accumulation to avoid truncation
errors. Accumulation of charge current above the maximum register value is reported at the maximum register
value (7FFFh); conversely, accumulation of discharge current below the minimum register value is reported at the
minimum value (8000h).

Charge currents (positive Current register values) less than 100μV are not accumulated in order to mask the effect
of accumulating small positive offset errors over long periods. This limits the minimum charge current, for coulomb­counting purposes, to 5mA for RSNS = 0.020Ω and 20mA for RSNS = 0.005Ω.

Read and write access is allowed to the ACR. The ACR must be written MSByte first then LSByte. Whenever the
ACR is written, the fractional accumulation result bits are cleared. The write must be completed within 3.515s (one
ACR register update period). A write to the ACR forces the ADC to perform an offset correction conversion and
update the internal offset correction factor. Current measurement and accumulation begins with the second
conversion following a write to the ACR. Writing ACR clears the fractional values in ACRL. The Format of the ACR
register is shown in Figure 8, and the format of ACRL is shown in Figure 9.

In order to preserve the ACR value in case of power loss, the ACR value is backed up to EEPROM. The ACR
value is recovered from EEPROM on power-up. See the Memory Map in Table 2 for specific address location and
backup frequency.

10 of 25

Figure 8. Accumulated Current Register Format, ACR

DS2782: Standalone Fuel Gauge IC

ACR

MSB—Address 10h LSB—Address 11h

15

2

214 213 212 211 210 29 28 27 26 25 24 23 22 21 20

MSb LSb MSb LSb

Units: 6.25μVh/Rsns

Figure 9. Fractional/Low Accumulated Current Register Format, ACRL

ACRL

MSB—Address 12h LSB—Address 13h

11

2

210 29 28 27 26 25 24 23 22 21 20 X X X X

MSb LSb MSb LSb

“X”: reserved Units:1.526nVHr/R

ACR LSb

R

VSS -

VSNS

20mΩ 15mΩ 10mΩ 5mΩ

SNS

R/W & EE

Read Only

SNS

6.25μVh 312.5μAh 416.7μAh 625μAh

1.250mAh

ACR RANGE

R

VSS -

VSNS

409.6mVh 20.48Ah 27.30Ah 40.96Ah 81.92Ah

20mΩ 15mΩ 10mΩ 5mΩ

SNS

ACCUMULATION BIAS

The Accumulation Bias register (AB) allows an arbitrary bias to be introduced into the current-accumulation
process. The AB can be used to account for currents that do not flow through the sense resistor, estimate currents
too small to measure, estimate battery self-discharge or correct for static offset of the individual DS2782 device.
The AB register allows a user programmed constant positive or negative polarity bias to be included in the current
accumulation process. The user-programmed two’s compliment value, with bit weighting the same as the current
register, is added to the ACR once per current conversion cycle. The AB value is loaded on power-up from
EEPROM memory. The format of the AB register is shown in Figure 10.

11 of 25

DS2782: Standalone Fuel Gauge IC

Figure 10. Accumulation Bias Register Formats

AB

S 26 25 24 23 22 21 20

MSb LSb

“S”: sign bit Units: 1.5625μV/Rsns

Address 61h

EE

CAPACITY ESTIMATION ALGORITHM

Remaining capacity estimation uses real-time measured values and stored parameters describing the cell
characteristics and application operating limits. The following diagram describes the algorithm inputs and outputs.

Figure 11. Top Level Algorithm Diagram

12 of 25

DS2782: Standalone Fuel Gauge IC

pty

pty

MODELING CELL CHARACTERISTICS

In order to achieve reasonable accuracy in estimating remaining capacity, the cell performance characteristics over
temperature, load current, and charge termination point must be considered. Since the behavior of Li-ion cells is
non-linear, even over a limited temperature range of 10°C to 35°C, these characteristics must be included in the
capacity estimation to achieve a reasonable accuracy. See Applications Note AN131 “Li+ Fuel Gauging with Dallas
Semiconductor Devices” for general information on the FuelPack™ method used in the DS2782. To facilitate
efficient implementation in hardware, a modified version of the method outlined in AN131 is used to store cell
characteristics in the DS2782. Full and empty points are retrieved in a lookup process which re-traces a piece-wise
linear model. Three model curves are stored: Full, Active Empty and Standby Empty. Each model curve is
constructed with 4 line segments and spans from 0°C to 40°C. Operation outside the 0°C to 40°C model span is
supported by the model with minimal loss of accuracy. Above 40°C, the 40°C fixed points are extended with zero
slope. This achieves a conservative capacity estimate for temperatures above 40°C. Below 0°C, the model curves
are extended using the slope of each 0°C to 10°C segment. If low temperature operation is expected, the 0°C to
10°C slopes can be selected to optimize the model accuracy. A diagram of example battery cell model curves is
shown if Figure 12.

Figure 12. Cell Model Example Diagram

100%

Derivative
[ppm / °C]

FULL

Cell
Characterization

Active

data points

Em

Standby
Em

1

0°C 10°C 20°C 30°C 40°C

2

3

4

Full: The Full curve defines how the full point of a given cell depends on temperature for a given charge

termination. The charge termination method used in the application is used to determine the table values. The
DS2782 reconstructs the Full line from cell characteristic table values to determine the Full capacity of the battery
at each temperature. Reconstruction occurs in one-degree temperature increments.

Active E mpty: The Active Empty curve defines the temperature variation in the empty point of the discharge profile

based on a high level load current (one that is sustained during a high power operating mode) and the minimum
voltage required for system operation. This load current is programmed as the Active Empty current (IAE), and
should be a 3.5s average value to correspond to values read from the Current register, and the specified minimum
voltage, or Active Empty voltage (VAE) should be a 220ms average to correspond to values read from the Voltage
register. The DS2782 reconstructs the Active Empty line from cell characteristic table values to determine the
Active Empty capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature
increments.

Standby Empty: The Standby Empty curve defines the temperature variation in the empty point in the discharge

defined by the application standby current and the minimum voltage required for standby operation. In typical PDA

FuelPack is a trademark of Dallas Semiconductor.

13 of 25

DS2782: Standalone Fuel Gauge IC

applications, Standby Empty represents the point that the battery can no longer support RAM refresh and thus the
standby voltage is set by the RAM voltage supply requirements. In other applications, Standby Empty can
represent the point that the battery can no longer support a subset of the full application operation, such as games
or organizer functions on a wireless handset. The standby load current and voltage are used for determining the
cell characteristics but are not programmed into the DS2782. The DS2782 reconstructs the Standby Empty line
from cell characteristic table values to determine the Standby Empty capacity of the battery at each temperature.
Reconstruction occurs in one-degree temperature increments.

CELL MODEL CONSTRUCTION

The model is constructed with all points normalized to the fully charged state at +40°C. Initial values, the +40°C
Full value in mVh units and the +40°C Active Empty value as a fraction of the +40°C Full are stored in the cell
parameter EEPROM block. Standby Empty at +40°C is by definition zero and therefore no storage is required. The
slopes (derivatives) of the 4 segments for each model curve are also stored in the cell parameter EEPROM block.
Segment endpoints are fixed at 0°C, +10°C, +20°C, +30°C and +40°C. An example of data stored in this manner is
shown in Table 1.

Table 1. Example Cell Characterization Table (Normalized to +40°C)

Manufacturers rated cell capacity: 1000mAh
Charge Voltage: 4.2V Charge Current: 500mA Termination Current: 50mA
Active Empty (V, I): 3.0V, 300mA Standby Empty (V, I): 3.0V, 4mA
Sense Resistor: 0.020Ω

Full 1051 0.927 0.951 0.974 0.991 1.0
Active Empty 0.051 0.040 0.022 0.012 0.008
Standby Empty 0.013 0.0067 0.0038 0.001 0

+40°C
Nominal
[mAh]

0°C +10°C +20°C +30°C +40°C

Figure 13. Lookup Function Diagram

Cell Model

Parameters

15 bytes

(EEPROM)

Temperature

Lookup

Function

FULL(T)

AE(T)

SE(T)

APPLICATION PARAMETERS

In addition to cell model characteristics, several application parameters are needed to detect the full and empty
points, as well as calculate results in mAh units.

Sense Resistor Prime (RSNSP): RSNSP stores the value of the sense resistor for use in computing the absolute

capacity results. The value is stored as a 1-byte conductance value with units of mhos. RSNSP supports resistor
values of 1Ω to 3.922mΩ. RSNSP is located in the Parameter EEPROM block.

Charge Voltage (VCHG): VCHG stores the charge voltage threshold used to detect a fully charged state. The

value is stored as a 1-byte voltage with units of 19.52mV and can range from 0V to 4.978V. VCHG should be set
marginally less than the cell voltage at the end of the charge cycle to ensure reliable charge termination detection.
VCHG is located in the Parameter EEPROM block.

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DS2782: Standalone Fuel Gauge IC

Minimum Charge Current (IMIN): IMIN stores the charge current threshold used to detect a fully charged state.

The value is stored as a 1-byte value with units of 50μV and can range from 0 to 12.75mV. Assuming RSNS =
20mΩ, IMIN can be programmed from 0mA to 637.5mA in 2.5mA steps. IMIN should be set marginally greater than
the charge current at the end of the charge cycle to ensure reliable charge termination detection. IMIN is located in
the Parameter EEPROM block.

Active Empty Voltage (VAE): VAE stores the voltage threshold used to detect the Active Empty point. The value

is stored in 1-byte with units of 19.52mV and can range from 0V to 4.978V. VAE is located in the Parameter

EEPROM block. See the Cell Characteristics section for more information.
Active Empty Current (IAE): IAE stores the discharge current threshold used to detect the Active Empty point.

The unsigned value represents the magnitude of the discharge current and is stored in 1-byte with units of 200μV
and can range from 0 to 51.2mV. Assuming RSNS = 20mΩ, IAE can be programmed from 0mA to 2550mA in

10mA steps. IAE is located in the Parameter EEPROM block. See the Cell Characteristics section for more

information.

Aging Capacity (AC): AC stores the rated battery capacity used in estimating the decrease in battery capacity that

occurs in normal use. The value is stored in 2-bytes in the same units as the ACR (6.25μVh). Setting AC to the
manufacturer’s rated capacity sets the aging rate to approximately 2.4% per 100 cycles of equivalent full capacity
discharges. Partial discharge cycles are added to form equivalent full capacity discharges. The default estimation
results in 88% capacity after 500 equivalent cycles. The estimated aging rate can be adjusted by setting AC to a
different value than the cell manufacturer’s rating. Setting AC to a lower value, accelerates the estimated aging.
Setting AC to a higher value, retards the estimated aging. AC is located in the Parameter EEPROM block.

Age Scalar (AS): AS adjusts the capacity estimation results downward to compensate for cell aging. AS is a 1-byte

value that represents values between 49.2% and 100%. The lsb is weighted at 0.78% (precisely 2

-7

). A value of
100% (128 decimal or 80h) represents an un-aged battery. A value of 95% is recommended as the starting AS
value at the time of pack manufacture to allow learning a larger capacity on batteries that have an initial capacity
greater than the nominal capacity programmed in the cell characteristic table. AS is modified by the cycle count
based age estimation introduced above and by the capacity Learn function. The host system has read and write
access to AS, however caution should exercised when writing AS to ensure that the cumulative aging estimate is
not over written with an incorrect value. Usually, writing AS by the host is not necessary because AS is

automatically saved to EEPROM on a periodic basis by the DS2782. (See the Memory section for details.) The

EEPROM stored value of AS is recalled on power-up.

CAPACITY ESTIMATION UTILITY FUNCTIONS

Aging Estimation

As discussed above, the AS register value is adjusted occasionally based on cumulative discharge. As the ACR
register decrements during each discharge cycle, an internal counter is incremented until equal to 32 times AC. AS
is then decremented by one, resulting in a decrease in the scaled full battery capacity of 0.78%. Refer to the AC
register description above for recommendations on customizing the age estimation rate.

Learn Function

Since Li+ cells exhibit charge efficiencies near unity, the charge delivered to a Li+ cell from a known empty point to
a known full point is a dependable measure of the cell capacity. A continuous charge from empty to full results in a

“learn cycle”. First, the Active Empty point must be detected. The Learn Flag (LEARNF) is set at this point. Then,

once charging starts, the charge must continue uninterrupted until the battery is charged to full. Upon detecting full,

LEARNF is cleared, the Charge to Full (CHGTF) flag is set and the Age Scalar (AS) is adjusted according to the

learned capacity of the cell.

ACR Housekeeping

The ACR register value is adjusted occasionally to maintain the coulomb count within the model curve boundaries.

When the battery is charged to full (CHGTF set), the ACR is set equal to the age scaled full lookup value at the

present temperature. If a learn cycle is in progress, correction of the ACR value occurs after the age scalar (AS) is
updated.

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DS2782: Standalone Fuel Gauge IC

When an empty condition is detected (AEF or LEARNF set), the ACR adjustment is conditional. If AEF is set and
LEARNF is not, then the Active Empty Point was not detected and the battery is likely below the Active Empty

capacity of the model. The ACR is set to the Active Empty model value only if it is greater than the Active Empty

model value. If LEARNF is set, then the battery is at the Active Empty Point and the ACR is set to the Active Empty

model value.

Full Detect

Full detection occurs when the Voltage (VOLT) readings remain continuously above the VCHG threshold for the
period between two Average Current (IAVG) readings, where both IAVG readings are below IMIN. The two
consecutive IAVG readings must also be positive and non-zero. This ensures that removing the battery from the

charger does not result in a false detection of full. Full Detect sets the Charge to Full (CHGTF) bit in the Status

register.

Active Empty Point Detect

Active Empty Point detection occurs when the Voltage register drops below the VAE threshold and the two
previous Current readings are above IAE. This captures the event of the battery reaching the Active Empty point.
Note that the two previous Current readings must be negative and greater in magnitude than IAE, that is, a larger
discharge current than specified by the IAE threshold. Qualifying the Voltage level with the discharge rate ensures
that the Active Empty point is not detected at loads much lighter than those used to construct the model. Also,
Active Empty must not be detected when a deep discharge at a very light load is followed by a load greater than
IAE. Either case would cause a learn cycle on the following charge to full to include part of the Standby capacity in

the measurement of the Active capacity. Active Empty detection sets the Learn Flag (LEARNF) bit in the Status

register.

RESULT REGISTERS

The DS2782 processes measurement and cell characteristics on a 3.5s interval and yields seven result registers.
The result registers are sufficient for direct display to the user in most applications. The host system can produce
customized values for system use, or user display by combining measurement, result and User EEPROM values.

FULL(T) [ ]: The Full capacity of the battery at the present temperature is reported normalized to the 40°C Full

value. This 15-bit value reflects the cell model Full value at the given temperature. FULL(T) reports values between
100% and 50% with a resolution of 61ppm (precisely 2

-14

). Though the register format permits values greater than

100%, the register value is clamped to a maximum value of 100%.

Active Empty, AE(T) [ ]: The Active Empty capacity of the battery at the present temperature is reported

normalized to the 40°C Full value. This 13-bit value reflects the cell model Active Empty at the given temperature.
AE(T) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2

-14

).

Standby Empty, SE(T) [ ]: The Standby Empty capacity of the battery at the present temperature is reported

normalized to the 40°C Full value. This 13-bit value reflects the cell model Standby Empty value at the current
temperature. SE(T) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2

-14

).

Remaining Active Absolute Capacity (RAAC) [mAh]: RAAC reports the capacity available under the current

temperature conditions at the Active Empty discharge rate (IAE) to the Active Empty point in absolute units of milli­amp-hours. RAAC is 16 bits.

Remaining Standby Absolute Capacity (RSAC) [mAh]: RSAC reports the capacity available under the current

temperature conditions at the Standby Empty discharge rate (ISE) to the Standby Empty point capacity in absolute
units of milli-amp-hours. RSAC is 16 bits.

Remaining Active Relative Capacity (RARC) [%]: RARC reports the capacity available under the current

temperature conditions at the Active Empty discharge rate (IAE) to the Active Empty point in relative units of
percent. RARC is 8 bits.

Remaining Standby Relative Capacity (RSRC) [%]: RSRC reports the capacity available under the current

temperature conditions at the Standby Empty discharge rate (ISE) to the Standby Empty point capacity in relative
units of percent. RSRC is 8 bits.

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DS2782: Standalone Fuel Gauge IC

Calculation of Results

RAAC [mAh] = (ACR[mVh] - AE(T) * FULL40[mVh]) * RSNSP [mhos]
RSAC [mAh] = (ACR[mVh] - SE(T) * FULL40[mVh]) * RSNSP [mhos]
RARC [%] = 100% * (ACR[mVh] - AE(T) * FULL40[mVh]) /

{(AS * FULL(T) - AE(T)) * FULL40[mVh]}

RSRC [%] = 100%* (ACR[mVh] - SE(T) * FULL40[mVh]) /

{(AS * FULL(T) - SE(T)) * FULL40[mVh]}

STATUS REGISTER

The STATUS register contains bits which report the device status. The bits can be set internally by the DS2782.
The CHGTF, AEF, SEF, LEARNF and VER bits are read only bits which can be cleared by hardware. The UVF and
PORF bits can only be cleared via the 2-Wire interface.

Figure 14. Status Register Format

Address 01h Bit Definition

Field Bit Format Allowable Values

Charge Termination Flag

CHGTF

AEF

SEF

LEARNF

7 Read Only

6 Read Only

5 Read Only

4 Read Only

Set to 1 when: ( VOLT > VCHG ) AND ( 0 < IAVG < IMIN ) continuously
for a period between two IAVG register updates ( 28s to 56s ).
Cleared to 0 when: RARC < 90%
Active Empty Flag
Set to 1 when: VOLT < VAE
Cleared to 0 when: RARC > 5%
Standby Empty Flag
Set to 1 when: RSRC < 10%
Cleared to 0 when: RSRC > 15%
Learn Flag – When set to 1, a charge cycle can be used to learn battery
capacity.
Set to 1 when: ( VOLT falls from above VAE to below VAE ) AND
( CURRENT > IAE )
Cleared to 0 when: ( CHGTF = 1 ) OR ( CURRENT < +100µV ) OR
( ACR = 0 **) OR ( ACR written or recalled from EEPROM) OR ( SLEEP
Entered )

Reserved

UVF

PORF
Reserved

* - This bit can be set by the DS2782, and may only be cleared via the 2-Wire interface.
** - LEARNF is only cleared if ACR reaches 0 after VOLT < VAE.

3 Read Only Undefined

Under-Voltage Flag

2 Read / Write *

1 Read / Write *

0 Read Only Undefined

Set to 1 when: VOLT < V
Cleared to 0 by: User
Power-On Reset Flag – Useful for reset detection, see text below.
Set to 1 upon Power-Up by hardware.
Cleared to 0 by: User

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SLEEP

DS2782: Standalone Fuel Gauge IC

CONTROL REGISTER

All CONTROL register bits are read and write accessible. The CONTROL register is recalled from Parameter
EEPROM memory at power-up. Register bit values can be modified in shadow RAM after power-up. Shadow RAM
values can be saved as the power up default values by using the Copy Data command.

Figure 15. Control Register Format

Address 60h Bit Definition

Field Bit Format Allowable Values

Reserved

UVEN

PMOD

Reserved

7 Undefined

Under Voltage SLEEP Enable

6 Read/Write

5 Read/Write

0:4 Undefined

0: Disables transition to SLEEP mode based on VIN voltage
1: Enables transition to SLEEP mode if,

VIN < V
Power Mode Enable
0: Disables transition to SLEEP mode based on SDA, SCL logic state
1: Enables transition to SLEEP mode if SDA, SCL at a logic low for
t

SLEEP

AND SDA, SCL stable at either logic level for t

SLEEP

SLEEP

SPECIAL FEATURE REGISTER

All Special Feature Register bits are read and write accessible, with default values specified in each bit definition.

Figure 16. Special Feature Register Format

Address 15h Bit Definition

Field Bit Format Allowable Values

Reserved

SAWE

PIOSC

2:7 Undefined

Slave Address Write Enable

1 Read/Write

0 Read/Write

0: Disables writes to the Slave Address Register
1: Enables writes to the Slave Address Register
Power-up default: 0 (writes disabled)
PIO Sense and Control
Read values
0: PIO pin ≤ Vil
1: PIO pin ≥ Vih
Write values
0: Activates PIO pin open-drain output driver, forcing the PIO pin low
1: Disables the output driver, allowing the PIO pin to be pulled high or

used as an input
Power-up and SLEEP mode default: 1 (PIO pin is hi-Z)
Note: PIO pin has weak pulldown

EEPROM REGISTER

The EEPROM register provides access control of the EEPROM blocks. EEPROM blocks can be locked to prevent
alteration of data within the block. Locking a block disables write access to the block. Once a block is locked, it
cannot be unlocked. Read access to EEPROM blocks is unaffected by the lock/unlock status.

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DS2782: Standalone Fuel Gauge IC

Figure 17. EEPROM REGISTER FORMAT

Address 1Fh Bit Definition

Field Bit Format Allowable Values

EEPROM Copy Flag
Set to 1 when: Copy Data command executed

EEC

LOCK

Reserved

BL1

BL0

7 Read Only

6

2:6 Undefined

1 Read Only

0 Read Only

Read /

Write to 1

Cleared to 0 when: Copy Data command completes
Note: While EEC = 1, writes to EEPROM addresses are ignored
Power-up default: 0
EEPROM Lock Enable
Host write to 1: Enables the Lock command. Host must issue Lock

command as next command after writing Lock Enable bit to 1.
Cleared to 0 when: Lock command completes or when Lock command

not the command issued immediately following the Write command

used to set the Lock Enable bit.
Power-up default: 0

EEPROM Block 1 Lock Flag (Parameter EEPROM 60h – 7Fh)
0: EEPROM is not locked
1: EEPROM block is locked
Factory default: 0
EEPROM Block 0 Lock Flag (User EEPROM 20h – 2Fh)
0: EEPROM is not locked
1: EEPROM block is locked
Factory default: 0

PROGRAMMABLE SLAVE ADDRESS

The 2-Wire slave address of the DS2782 is stored in the parameter EEPROM block, address 7Eh. Programming
the slave address requires a write to set the SAWE (Slave Address Write Enable) bit in the Special Features
register, followed by a write to 7Eh with the desired slave address. The new slave address value is effective
following the write to 7Eh, and must be used to address the DS2782 on subsequent bus transactions. The slave
address value is not stored to EEPROM until a Copy EEPROM block 1 command is executed. Prior to executing
the Copy command, power cycling the DS2782 restores the original slave address value. The data format of the
slave address value in address 7Eh is shown in Figure 18. When not writing the slave address, the SAWE bit
should be written to a 0.

Figure 18. Slave Address Format

ADDRESS 7E

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

A6 A5 A4 A3 A2 A1 A0 X

A6-A0: Slave Address. A6-A0 contains the 7-bit slave address of the DS2782. The factory default is 0110100b.
X: Reserved Bits.

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DS2782: Standalone Fuel Gauge IC

MEMORY

The DS2782 has a 256 byte linear memory space with registers for instrumentation, status, and control, as well as
EEPROM memory blocks to store parameters and user information. Byte addresses designated as “Reserved”
return undefined data when read. Reserved bytes should not be written. Several byte registers are paired into two­byte registers in order to store 16-bit values. The most significant byte (MSB) of the 16 bit value is located at a
even address and the least significant byte (LSB) is located at the next address (odd) byte. When the MSB of a
two-byte register is read, the MSB and LSB are latched simultaneously and held for the duration of the read data
command to prevent updates to the LSB during the read. This ensures 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.

EEPROM memory consists of the NV EEPROM cells overlaid with volatile shadow RAM. The Read Data and Write
Data commands allow the 2-Wire interface to directly accesses only the shadow RAM. The Copy Data and Recall
Data function commands transfer data between the shadow RAM and the EEPROM cells. In order to modify the
data stored in the EEPROM cells, data must be written to the shadow RAM and then copied to the EEPROM. In
order to verify the data stored in the EEPROM cells, the EEPROM data must be recalled to the shadow RAM and
then read from the shadow RAM. See Figure 19.

USER EEPROM

A 16 byte User EEPROM memory (block 0, addresses 20h - 2Fh) provides NV memory that is uncommitted to
other DS2782 functions. Accessing the User EEPROM block does not affect the operation of the DS2782. User
EEPROM is lockable, and once locked, write access is not allowed. The battery pack or host system manufacturer
can program lot codes, date codes and other manufacturing, warranty, or diagnostic information and then lock it to
safeguard the data. User EEPROM can also store parameters for charging to support different size batteries in a
host device as well as auxiliary model data such as time to full charge estimation parameters.

PARAMETER EEPROM

Model data for the cells, as well as application operating parameters are stored in the Parameter EEPROM

memory (block 1, addresses 60h - 7Fh). The ACR (MSB and LSB) and AS registers are automatically saved to
EEPROM when the RARC result crosses 4% boundaries. This allows the DS2782 to be located outside the

protection FETs. In this manner, if a protection device is triggered, the DS2782 cannot lose more that 4% of charge
or discharge data.

Figure 19. EEPROM Access via Shadow RAM

Copy

Serial

Interface

Read

Write

EEPROM

Shadow RAM

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Recall

DS2782: Standalone Fuel Gauge IC

Table 2. MEMORY MAP

ADDRESS (HEX) DESCRIPTION READ/WRITE

00 Reserved R

01 STATUS - Status Register R/W
02 RAAC - Remaining Active Absolute Capacity MSB R
03 RAAC - Remaining Active Absolute Capacity LSB R
04 RSAC - Remaining Standby Absolute Capacity MSB R
05 RSAC - Remaining Standby Absolute Capacity LSB R
06 RARC - Remaining Active Relative Capacity R
07 RSRC - Remaining Standby Relative Capacity R
08 IAVG - Average Current Register MSB R

09 IAVG - Average Current Register LSB R
0A TEMP - Temperature Register MSB R
0B TEMP - Temperature Register LSB R
0C VOLT - Voltage Register MSB R
0D VOLT - Voltage Register LSB R
0E CURRENT - Current Register MSB R

0F CURRENT - Current Register LSB R

10 ACR - Accumulated Current Register MSB R/W*

11 ACR - Accumulated Current Register LSB R/W*

12 ACRL - Low Accumulated Current Register MSB R

13 ACRL - Low Accumulated Current Register LSB R

14 AS - Age Scalar R/W*

15 SFR - Special Feature Register R/W

16 FULL - Full Capacity MSB R

17 FULL - Full Capacity LSB R

18 AE - Active Empty MSB R

19 AE - Active Empty LSB R
1A SE - Standby Empty MSB R
1B SE - Standby Empty LSB R

1C to 1E Reserved —

1F EEPROM - EEPROM Register R/W

20 to 2F User EEPROM, Lockable, Block 0 R/W

30 to 37 Additional User EEPROM, Lockable, Block 0 R/W+

38 to 5F Reserved —

60 to 7F Parameter EEPROM, Lockable, Block 1 R/W

80 to EF Reserved —

F0 to F7 Unique ID R+

80 to FF Reserved —

FE Function Command Register W

FF Reserved —

* Register value is automatically saved to EEPROM during ACTIVE mode operation and recalled from EEPROM on power up.

+ Unique 64 bit ID is a factory option available by special order. Units with IDs do not allow access to additional user EEPROM block 0.

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DS2782: Standalone Fuel Gauge IC

Table 3. PARAMETER EEPROM MEMORY BLOCK 1

ADDRESS

(HEX)

60 CONTROL - Control Register 70 AE 3040 Slope
61 AB - Accumulation Bias 71 AE 2030 Slope
62 AC - Aging Capacity MSB 72 AE 1020 Slope
63 AC - Aging Capacity LSB 73 AE 0010 Slope
64 VCHG - Charge Voltage 74 SE 3040 Slope
65 IMIN - Minimum Charge Current 75 SE 2030 Slope
66 VAE - Active Empty Voltage 76 SE 1020 Slope
67 IAE - Active Empty Current 77 SE 0010 Slope
68 Active Empty 40 78 RSGAIN - Sense Resistor Gain MSB
69 RSNSP - Sense Resistor Prime 79 RSGAIN - Sense Resistor Gain LSB
6A Full 40 MSB 7A RSTC - Sense Resistor Temp. Coeff.
6B Full 40 LSB 7B FRSGAIN - Factory Gain MSB

6C Full 3040 Slope 7C FRSGAIN - Factory Gain LSB

6D Full 2030 Slope 7D Reserved

6E Full 1020 Slope 7E 2-Wire Slave Address

6F Full 0010 Slope 7F Reserved

DESCRIPTION ADDRESS

(HEX)

DESCRIPTION

2-WIRE BUS SYSTEM

The 2-Wire bus system supports operation as a slave only device in a single or multi-slave, and single or multi­master system. Up to 128 slave devices may share the bus by uniquely setting the 7-bit slave address. The 2-wire
interface consists of a serial data line (SDA) and serial clock line (SCL). SDA and SCL provide bidirectional
communication between the DS2782 slave device and a master device at speeds up to 400 kHz. The DS2782’s
SDA pin operates bi-directionally, that is, when the DS2782 receives data, SDA operates as an input, and when the
DS2782 returns data, SDA operates as an open drain output, with the host system providing a resistive pull-up.
The DS2782 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.

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 multi-master 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.

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DS2782: Standalone Fuel Gauge IC

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 DS2782 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 re­attempt 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. DS2782 registers composed of multi-byte values are ordered most significant
byte (MSB) first. The MSB of multi-byte 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 DS2782 continuously monitors for a
START condition followed by its slave address. When the DS2782 receives a slave address that matches the value
in its Programmable Slave Address register, it responds with an Acknowledge bit during the clock period following
the R/W bit. The 7-bit Programmable Slave Address register is factory programmed to 0110100. The slave address
can be re-programmed, refer to the Programmable Slave Address section for details.

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 stave by the master.

Bus Timing

The DS2782 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 DS2782. 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 4. 2-Wire Protocol Key

KEY DESCRIPTION KEY DESCRIPTION

S START bit Sr Repeated START
SAddr Slave Address (7-bit) W R/W bit = 0
FCmd Function Command byte R R/W bit = 1
MAddr Memory Address byte P STOP bit
Data Data byte written by master Data Data byte returned by slave
A Acknowledge bit - Master A Acknowledge bit - Slave
N No Acknowledge - Master N No Acknowledge - Slave

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DS2782: Standalone Fuel Gauge IC

Basic Transaction Formats

Write: S SAddr W A MAddr A Data0 A P

A write transaction transfers one or more data bytes to the DS2782. 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 DS2782. 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 DS2782 beginning with
the Slave Address Acknowledge cycle. Control of the SDA signal is retained by the DS2782 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 DS2782 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 DS2782 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 DS2782, 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 DS2782 ignores the data. Data is also ignored on writes to read-only addresses and
reserved addresses, locked EEPROM blocks 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 DS2782 are not written to
memory. As noted in the Memory Section, writes to unlocked EEPROM blocks modify the shadow RAM only.

Read Data Protocol

The Read Data protocol is used to read register and shadow RAM data from the DS2782 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 most significant bit (msb) of the data in MAddr. Because the address is
automatically incremented after the least significant bit (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 DS2782 outputs data values of FFh. Addresses labeled
“Reserved” in the memory map 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.

Function Command Protocol

The Function Command protocol executes a device specific operation by writing one of the function command
values (FCmd) to memory address FEh. Table 5 lists the DS2782 FCmd values and describes the actions taken by
each. A one byte write protocol is used to transmit the function command, with the MAddr set to FEh and the data

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DS2782: Standalone Fuel Gauge IC

byte set to the desired FCmd value. Additional data bytes are ignored. Data read from memory address FEh is
undefined.

S SAddr W A MAddr=0FEh A FCmd A P

Table 5. Function Commands

FUNCTION

COMMAND

Copy Data

Recall Data

TARGET

EEPROM

BLOCK

FCMD

VALUE

0 42h

1 44h

0 B2h

DESCRIPTION

This command copies the shadow RAM to the target EEPROM block.
Copy Data commands that target locked blocks are ignored. While the
Copy Data command is executing, the EEC bit in the EEPROM register is
set to 1, and Write Data commands with MAddr set to any address within
the target block are ignored. Read Data and Write Data commands with
MAddr set outside the target block are processed while the copy is in
progress. The Copy Data command execution time, t
and starts after the FCMD byte is acknowledged. Subsequent Copy or
Lock commands must be delayed until the EEPROM programming cycle

completes.

This command recalls the contents of the targeted EEPROM block to its

shadow RAM.

, is 2ms typical

EEC

1 B4h

This command locks (write-protects) the targeted EEPROM block. The

0 63h

Lock

1 66h

LOCK bit in the EEPROM register must be set to 1 before the lock
command is executed. If the LOCK bit is 0, the lock command has no
effect. The lock command is permanent; a locked block can never be
written again. The Lock command execution time, t
starts after the FCMD byte is acknowledged. Subsequent Copy or Lock
commands must be delayed until the EEPROM programming cycle

completes.

, is 2ms typical and

EEC

64-BIT UNIQUE ID

The DS2782 can be special ordered with a unique, factory-programmed ID that is 64 bits in length. The first eight
bits are the product family code (B2h for DS2782). The next 48 bits are a unique 40-bit serial number followed by
0x82h. The last eight bits are a cyclic redundancy check (CRC) of the first 56 bits (see Figure 16). The 64-bit ID
can be read as 8 bytes starting at memory address F0h. The 64-bit ID is read only.

Figure 16. 64-BIT ID FORMAT

8-BIT CRC 48-BIT SERIAL NUMBER

8-BIT FAMILY
CODE (B2h)

msb lsb

PACKAGE INFORMATION

(For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.)

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