DS2786BG+TR [MAXIM]

Stand-Alone OCV-Based Fuel Gauge; 独立式基于OCV电量计
DS2786BG+TR
型号: DS2786BG+TR
厂家: MAXIM INTEGRATED PRODUCTS    MAXIM INTEGRATED PRODUCTS
描述:

Stand-Alone OCV-Based Fuel Gauge
独立式基于OCV电量计

仪表
文件: 总21页 (文件大小:369K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
19-5223; Rev 1; 4/10  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
General Description  
Features  
Relative Capacity Calculated from Combination  
Coulomb Counter and Open-Circuit Cell Voltage  
(OCV) Battery Model  
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.  
Accurate Warning of Low-Battery Conditions  
Even on First Cycle (No Learn Cycle Needed)  
12-Bit Battery Voltage Measurement  
±1ꢀmV Accuracy  
1.22mV LSB, ꢀV to 4.5V Input Range  
11-Bit Bidirectional Current Measurement  
25µV LSB, ±51.2mV ꢁynamic Range  
1.67mA LSB, ±±.4A (R  
= 15mΩ)  
SNS  
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.  
Current Accumulation Measurement Resolution  
±2ꢀ4.ꢂmVꢃ Range  
±1±.65Aꢃ (R  
= 15mΩ)  
SNS  
Internal Temperature Measurement  
ꢀ.125°C LSB, ±±°C Accuracy  
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.  
Two 11-Bit Auxiliary Input-Voltage Measurements  
±ꢂ LSB Accuracy, Ratiometric Inputs Eliminate  
Supply Accuracy Issues  
V  
Pin ꢁrives Resistive ꢁividers, Reduces  
OUT  
Current Consumption  
2-Wire Interface  
Low Power Consumption  
The DS2786B comes in a 10-pin, lead-free, TDFN 3mm  
x 3mm package with an exposed pad (EP).  
Active Current: 5ꢀµA (typ), ꢂꢀµA (max)  
Sleep Current: 1µA (typ), ±µA (max)  
Ordering Information  
Applications  
3G Multimedia Wireless Handsets  
PART  
DS2786BG+  
TEMP RANGE  
-20°C to +70°C  
-20°C to +70°C  
PIN-PACKAGE  
10 TDFN-EP*  
10 TDFN-EP*  
Digital Still Cameras  
Digital Audio (MP3) Players  
DS2786BG+T&R  
+Denotes a lead(Pb)-free/RoHS-compliant package.  
*EP = Exposed pad.  
T&R = Tape and reel.  
Operating Diagram  
V
IN  
SYSTEM  
μP  
V
OUT  
DS2786B  
2
Li+  
I C  
INTERFACE  
SDA  
SCL  
SNS  
AIN0  
AIN1  
PROTECTION  
CIRCUIT  
V
SS  
R
SNS  
(EEPROM PROGRAMMING TEST POINT NOT SHOWN)  
________________________________________________________________ Maxim Integrated Products  
1
For pricing, delivery, and ordering information, please contact Maxim ꢁirect at 1-ꢂꢂꢂ-629-4642,  
or visit Maxim’s website at www.maxim-ic.com.  
Stand-Alone OCV-Based Fuel Gauge  
ABSOLUTE MAXIMUM RATINGS  
Voltage on All Pins Except V  
Relative to V ...-0.3V to +6V  
Storage Temperature Range.............................-55°C to +125°C  
Lead Temperature (soldering, 10s) .................................+300°C  
Soldering Temperature (reflow) .......................................+260°C  
PROG  
SS  
Voltage on V  
Relative to V ..........................-0.3V to +18V  
PROG  
SS  
Operating Temperature Range ...........................-40°C to +85°C  
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.  
DS2786B  
RECOMMENꢁEꢁ ꢁC OPERATING PROCEꢁURE  
(2.5V V  
4.5V, T = -20°C to +70°C.)  
A
DD  
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
+2.5  
-0.3  
-0.3  
TYP  
MAX  
+4.5  
UNITS  
Supply Voltage  
Data I/O Pins  
V
(Note 1)  
V
V
V
DD  
SCL, SDA (Note 1)  
+4.5  
Programming Pin  
V
(Note 1)  
(Note 1)  
+15.5  
PROG  
V
, AIN0,  
IN  
V
+
DD  
V
, AIN0, AIN1 Pin  
-0.3  
V
IN  
AIN1  
0.3  
ꢁC ELECTRICAL CHARACTERISTICS  
(2.5V V  
4.5V, T = -20°C to +70°C, unless otherwise noted.)  
A
DD  
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
50  
MAX  
75  
UNITS  
Active Current  
I
μA  
ACTIVE  
V
= 2.0V, SCL, SDA = V  
0.3  
1
1.0  
3
DD  
SS  
Sleep-Mode Current  
I
μA  
μV  
SLEEP  
SCL, SDA = V  
SS  
Current-Measurement Resolution  
I
25  
LSB  
Current-Measurement  
Full-Scale Magnitude  
I
(Note 1)  
(Note 2)  
51.2  
mV  
FS  
Current-Measurement  
Offset Error  
I
I
-50  
+50  
μV  
OERR  
GERR  
% of  
reading  
Current-Measurement Gain Error  
Timebase Accuracy  
Voltage Error  
-1.5  
+1.5  
V
T
= 3.6V at +25°C  
-1  
-2  
+1  
+2  
DD  
t
%
= 0°C to +70°C  
ERR  
A
T
A
= -20°C to +70°C  
-3  
+3  
V
= V = 3.6V, T = 0°C to +50°C  
-10  
-20  
15  
+10  
+20  
DD  
IN  
A
V
mV  
M  
LSB  
GERR  
T
A
= -20°C to +70°C  
Input Resistance V , AIN0, AIN1  
IN  
R
IN  
AIN0, AIN1 Error  
-8  
+8  
V
0.5  
-
DD  
V
V
Output Drive  
I
= 1mA  
O
V
OUT  
OUT  
Precharge Time  
t
13.2  
-3  
13.7  
14.2  
+3  
ms  
°C  
PRE  
Temperature Error  
T
ERR  
2
_______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
ꢁC ELECTRICAL CHARACTERISTICS (continued)  
(2.5V V  
4.5V, T = -20°C to +70°C, unless otherwise noted.)  
A
DD  
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
V
Input Logic-High: SCL, SDA  
Input Logic-Low: SCL, SDA  
Output Logic-Low: SDA  
V
(Note 1)  
(Note 1)  
1.4  
IH  
V
0.6  
0.4  
1.0  
V
IL  
V
I
= 4mA (Note 1)  
V
OL  
PD  
OL  
Pulldown Current: SCL, SDA  
I
V
= 4.2V, V  
= 0.4V  
PIN  
0.2  
20  
μA  
kꢀ  
pF  
s
DD  
V
Pulldown  
R
VPROG  
PROG  
Input Capacitance: SCL, SDA  
Bus Low Timeout  
C
50  
2.2  
15  
2
BUS  
t
(Note 3)  
1.5  
14  
SLEEP  
EEPROM Programming Voltage  
EEPROM Programming Current  
EEPROM Programming Time  
EEPROM Copy Endurance  
V
V
PROG  
PROG  
PROG  
I
t
mA  
ms  
Writes  
3.1  
14  
100  
ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE  
(2.5V V  
4.5V, T = -20°C to +70°C.)  
A
DD  
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
SCL Clock Frequency  
f
(Note 4)  
(Note 5)  
0
400  
kHz  
SCL  
Bus Free Time Between a STOP  
and START Condition  
t
1.3  
0.6  
μs  
μs  
BUF  
Hold Time (Repeated)  
START Condition  
t
t
HD:STA  
Low Period of SCL Clock  
High Period of SCL Clock  
t
1.3  
0.6  
μs  
μs  
LOW  
t
HIGH  
Setup Time for a Repeated  
START Condition  
0.6  
μs  
SU:STA  
Data Hold Time  
Data Setup Time  
t
(Notes 6, 7)  
(Note 6)  
0
0.9  
μs  
ns  
HD:DAT  
t
100  
SU:DAT  
Rise Time of Both SDA and  
SCL Signals  
20 +  
t
300  
300  
ns  
R
0.1C  
B
Fall Time of Both SDA and  
SCL Signals  
20 +  
t
ns  
μs  
ns  
F
0.1C  
B
Setup Time for STOP Condition  
t
SU:STO  
0.6  
Spike Pulse Widths Suppressed  
by Input Filter  
t
SP  
(Note 8)  
(Note 9)  
0
50  
Capacitive Load for Each Bus Line  
SCL, SDA Input Capacitance  
C
400  
60  
pF  
pF  
B
C
BIN  
Note 1: All voltages are referenced to V  
.
SS  
Note 2: Offset specified after autocalibration cycle and Current Offset Bias Register = 00h.  
Note ±: The DS2786B enters the sleep mode 1.5s to 2.2s after (SCL < V ) and (SDA < V ).  
IL  
IL  
Note 4: Timing must be fast enough to prevent the DS2786B from entering sleep mode due to bus low for period > t  
.
SLEEP  
Note 5: f  
must meet the minimum clock low time plus the rise/fall times.  
SCL  
_______________________________________________________________________________________  
±
Stand-Alone OCV-Based Fuel Gauge  
ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (continued)  
(2.5V V  
4.5V, T = -20°C to +70°C.)  
A
DD  
Note 6: The maximum t  
has only to be met if the device does not stretch the low period (t  
) of the SCL signal.  
HD:DAT  
LOW  
Note 7: This device internally provides a hold time of at least 100ns for the SDA signal (referred to the V  
of the SCL signal) to  
IHMIN  
bridge the undefined region of the falling edge of SCL.  
Note ꢂ: Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant.  
Note 9: C —total capacitance of one bus line in pF.  
B
DS2786B  
SDA  
t
F
t
SP  
t
t
t
F
R
BUF  
t
SU;DAT  
t
t
t
R
HD;STA  
LOW  
SCL  
t
t
t
SU;STO  
HD;STA  
SU;STA  
t
HD;DAT  
P
S
Sr  
S
Figure 1. 2-Wire Bus Timing Diagram  
4
_______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
Pin Configuration  
TOP VIEW  
AIN1  
AIN0  
SCL  
SDA  
SNS  
1
2
3
4
5
10  
9
V
V
V
V
V
DD  
IN  
8
OUT  
PROG  
SS  
DS2786B  
7
EP  
6
TDFN  
(3mm x 3mm)  
Pin Description  
PIN  
1
NAME  
AIN1  
FUNCTION  
Auxiliary Voltage Input Number 1  
Auxiliary Voltage Input Number 0  
2
AIN0  
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.  
3
4
SCL  
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.  
SDA  
SNS  
5
6
Current-Sense Input. Connect to the handset side of the sense resistor.  
Device Ground. Connect to the battery side of the sense resistor.  
V
SS  
EEPROM Programming Voltage Input. Connect to external supply for production programming.  
Connect to V during normal operation.  
SS  
7
V
PROG  
Voltage Out. Supply for auxiliary input voltage measurement dividers. Connect to high side of  
resistor-divider circuits.  
8
9
V
OUT  
V
Battery Voltage Input. The voltage of the cell pack is measured through this pin.  
IN  
Power-Supply Input. 2.5V to 4.5V Input Range. Connect to system power through a decoupling  
network.  
10  
V
DD  
EP  
Exposed Pad. Connect to V  
.
SS  
_______________________________________________________________________________________  
5
Stand-Alone OCV-Based Fuel Gauge  
magnitude in the 2-byte Current Register. Battery-  
Detailed Description  
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.  
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 25ꢀV. Assuming  
a 15mΩ sense 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  
DS2786B  
SWITCH IS ON WHEN AIN0 OR AIN1 IS BEING MEASURED.  
V
V
DD  
OUT  
BIAS  
TIMEBASE  
VOLTAGE  
REFERENCE  
EEPROM  
V
PROG  
STATE  
MACHINE  
ADC  
TEMPERATURE  
MEASUREMENT  
SDA  
SCL  
2-WIRE  
INTERFACE  
1kΩ  
1kΩ  
SNS  
AIN1  
V
SS  
V
AIN0  
IN  
IC  
GROUND  
Figure 2. Block Diagram  
6
_______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
BATTERY  
SYSTEM  
SYSTEM  
VDD  
PACK+  
150Ω  
1kΩ  
V
V
V
IN  
OUT  
PROGRAMMING  
TEST POINT  
DD  
V
PROG  
1kΩ  
1kΩ  
10nF  
(1) 5.6V  
DS2786B  
AIN0  
AIN1  
SYSTEM  
SERIAL  
BUS  
PACKID  
THERM  
SDA  
SCL  
SNS  
V
SS  
PROTECTION IC  
(Li+/POLYMER)  
R
SNS  
SYSTEM  
VSS  
PACK-  
(1) OPTIONAL FOR 8kV/15kV ESD  
2.5V  
(1)  
1nF  
1nF  
Figure 3. Application Example  
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-  
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 > V ) or (SDA > V )  
IH  
IH  
The DS2786B operating mode transitions from Active to  
Sleep when:  
2
tiple-cell vendors. The I C interface also allows  
SMOD = 1 and (SCL < V ) and (SDA < V )  
IL  
SLEEP  
IL  
read/write access to the Status, Configuration, and  
Measurement Registers.  
for t  
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.  
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  
_______________________________________________________________________________________  
7
Stand-Alone OCV-Based Fuel Gauge  
the V  
output voltage to settle. The DS2786B can be  
OUT  
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  
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, V  
is not activated. A full sequence of voltage  
OUT  
DS2786B is in Active Mode. The V  
pin is activated  
OUT  
measurements nominally takes 1760ms to complete.  
t
before the AIN0 and AIN1 conversion to allow for  
PRE  
DS2786B  
V
PIN  
IN  
AVERAGE OVER 440ms  
MEASUREMENT  
0.86ms  
DELAY  
VOLTAGE  
REGISTER  
NEW REGISTER VALUE  
ACTIVE  
INACTIVE  
INACTIVE  
V
PIN  
OUT  
(INACTIVE FOR TEMPERATURE MEASUREMENT)  
t
PRE  
ALTERNATING AIN0 OR  
AIN1/TEMPERATURE  
MEASUREMENT  
AVERAGE OVER 220ms  
0.86ms  
DELAY  
AIN0 OR AIN1/  
TEMPERATURE REGISTER  
NEW REGISTER VALUE  
DIFFERENTIAL  
CURRENT  
AVERAGE OVER 220ms  
MEASUREMENT  
0.86ms  
DELAY  
0.86ms  
DELAY  
CURRENT  
REGISTER  
NEW REGISTER VALUE  
440ms  
220ms  
220ms  
CYCLE OF MEASUREMENTS REPEATS EVERY 880ms.  
Figure 4. Measurement Sequence  
_______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
conversion is displayed in the Voltage Register. The  
OCV algorithm automatically adjusts for the effects of  
the offset-correction cycle.  
Voltage Measurement  
Battery voltage is measured at the V input with respect  
IN  
to V over a 0 to 4.999V range and with a resolution of  
SS  
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.  
Auxilary Input Measurements  
The DS2786B has two auxiliary voltage-measurement  
inputs, AIN0 and AIN1. Both are measured with respect  
to V . These inputs are designed for measuring resis-  
SS  
The input impedance of V  
is sufficiently large  
IN  
tor ratios, particularly useful for measuring thermistor or  
pack identification resistors. Prior to the beginning of a  
(> 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  
measurement cycle on AIN0 or AIN1, the V  
pin out-  
OUT  
puts a reference voltage in order to drive a resistive  
divider formed by a known resistor value, and the  
unknown resistance to be measured. This technique  
delivers good accuracy at a reasonable cost, as it  
removes reference tolerance from the error calcula-  
tions. Measurements alternate between each input.  
Each auxiliary measurement is therefore updated every  
1760ms and placed in the corresponding AIN0 or AIN1  
Register in two’s-complement form. Figure 6 shows the  
Auxiliary Input Registers format.  
voltage to the V input.  
IN  
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 V  
IN  
signal. The voltage measurement just prior to the offset  
MSB—ADDRESS 0Ch  
LSB—ADDRESS 0Dh  
S
211  
210  
29  
28  
27  
26  
25  
24  
23  
22  
21  
20  
X
X
X
MSB  
LSB  
MSB  
LSB  
“S”: SIGN BIT(S), “X”: RESERVED  
UNITS: 1.22mV  
Figure 5. Voltage Register Format  
AIN0  
S
MSB—ADDRESS 08h  
28 27 26 25  
LSB—ADDRESS 09h  
20  
210  
29  
24  
23  
22  
21  
X
X
X
X
MSB  
LSB  
MSB  
LSB  
“S”: SIGN BIT, “X”: RESERVED  
UNITS: V  
× 1/2047  
OUT  
AIN1  
S
MSB—ADDRESS 0Ah  
28 27 26 25  
LSB—ADDRESS 0Bh  
20  
210  
29  
24  
23  
22  
21  
X
X
X
X
MSB  
LSB  
MSB  
LSB  
“S”: SIGN BIT, “X”: RESERVED  
UNITS: V  
× 1/2047  
OUT  
Figure 6. Auxiliary Input Registers Format  
_______________________________________________________________________________________  
9
Stand-Alone OCV-Based Fuel Gauge  
input as long as the continuous or average signal level  
Temperature Measurement  
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).  
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.  
DS2786B  
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  
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  
current-sense resistor, R  
, connected between the  
SNS  
SNS and V pins. The voltage-sense range between  
SS  
SS  
SNS and V is 51.2mV. Note that positive current val-  
ues occur when V  
is less than V , and negative  
SS  
SNS  
current values occur when V  
is greater than V  
.
SS  
SNS  
R
values.  
SNS  
Peak signal amplitudes up to 102mV are allowed at the  
MSB—ADDRESS 0Ah  
LSB—ADDRESS 0Bh  
20  
S
29  
28  
27  
26  
25  
24  
23  
22  
21  
X
X
X
X
X
MSB  
LSB  
MSB  
LSB  
“S”: SIGN BIT(S), “X”: RESERVED  
UNITS: 0.125°C  
Figure 7. Temperature Register Format  
MSB—ADDRESS 0Eh  
29 28 27 26  
LSB—ADDRESS 0Fh  
20  
S
210  
25  
24  
23  
22  
21  
X
X
X
X
MSB  
LSB  
MSB  
LSB  
“S”: SIGN BIT  
UNITS: 25μV/R  
SNS  
Figure 8. Current Register Formats  
Table 1. Current Range and Resolution for Various R  
Values  
SNS  
CURRENT RESOLUTION (1 LSB)  
CURRENT INPUT RANGE  
R
R
SNS  
SNS  
|V - V  
SS  
|
V
- V  
SS SNS  
SNS  
20mꢀ  
15mꢀ  
10m  
5mꢀ  
20mꢀ  
15mꢀ  
10mꢀ  
5mꢀ  
1.25mA  
25μV  
1.667mA  
2.5mA  
5mA  
51.2mV  
2.56A  
3.41A  
5.12A  
10.24A  
1ꢀ ______________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
Current Offset Bias  
Table 2. Accumulated Current Range for  
Various R Values  
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.  
SNS  
IACR RANGE  
R
SNS  
V
- V  
SNS  
SS  
20mꢀ  
10.24Ah  
15mꢀ  
13.65Ah  
10mꢀ  
5mꢀ  
204.8mVh  
20.48Ah  
40.96Ah  
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.  
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 25ꢀV 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 Relative Capacity Register reports remaining cell  
charge as a percentage of full. Relative capacity is  
reported with a resolution of 0.5% and is limited to a  
value between 0% and 100%. The Relative Capacity  
Register is updated each time the IC performs a current  
measurement or open-circuit cell-voltage measurement.  
See Figure 10.  
ADDRESS 02h  
27  
26  
25  
24  
23  
22  
21  
20  
the accumulated current range for various R  
values.  
SNS  
MSB  
LSB  
ADDRESS 60h  
UNITS: 0.5%  
S
26  
25  
24  
23  
22  
21  
20  
Figure 10. Relative Capacity Register Format  
MSB  
LSB  
“S”: SIGN BIT  
UNITS: 25μV/R  
SNS  
Figure 9. Current Offset Bias Register Format  
______________________________________________________________________________________ 11  
Stand-Alone OCV-Based Fuel Gauge  
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).  
operational current, but above the maximum idle cur-  
rent of the application should be selected. The OCV  
Threshold Register has a resolution of 25ꢀV/R , and  
SNS  
. The factory  
a range from 0mV/R  
to 6.375mV/R  
SNS  
SNS  
default value is 28h. See Figure 13 for the OCV thresh-  
old register format.  
While the measured current is below the OCV threshold  
level, the DS2786B actively searches for a relaxed cell  
by calculating the change in cell voltage as reported in  
the Voltage Register over 7.5min intervals (dV/dt). If the  
7.5min dV/dt change of an average of four Voltage  
Register readings is less than the value stored in the  
OCV dV/dt Threshold Register, the DS2786B deter-  
mines that the cell is now in a relaxed state and the  
Relative Capacity Register is adjusted based on the  
OCV cell model stored in parameter EEPROM. This  
operation occurs repeatedly every 7.5min up to 1hr  
after the cell enters a relaxed state.  
Each Capacity Scaling Factor Register has a resolution  
of 78.125%/Vh and a maximum range of 0 to  
19921.875%/Vh. During assembly, the Initial Capacity  
Register should be programmed to the capacity of the  
cell. For example, an application using a 1Ah cell and  
0.015Ω sense resistor would set the Initial Capacity  
Register to a value of (100%/(1Ah x 0.015Ω))/  
78.125%/Vh = 55h. The Learned Capacity Scaling Factor  
Register is controlled by the DS2786B. The power-up  
value is 00h, and the register is updated with the calcu-  
lated new cell capacity value after every learn operation.  
See Figures 11 and 12.  
DS2786B  
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.  
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  
ADDRESS 7Ah  
ADDRESS 7Bh  
27  
26  
25  
24  
23  
22  
21  
20  
27  
26  
25  
24  
23  
22  
21  
20  
MSB  
LSB  
MSB  
LSB  
UNITS: 78.125%/Vh  
UNITS: 25μV/R  
SNS  
Figure 11. Initial Capacity Scaling Factor Register Format  
Figure 13. OCV Threshold Register Format  
ADDRESS 17h  
ADDRESS 7Ch  
27  
26  
25  
24  
23  
22  
21  
20  
SMOD LDIS VODIS ITEMP  
MSB  
23  
22  
21  
20  
MSB  
LSB  
LSB  
UNITS: 78.125%/Vh  
UNITS: 0.61mV/7.5min  
Figure 12. Learned Capacity Scaling Factor Register Format  
Figure 14. OCV dV/dt Threshold Register Format  
12 ______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
Capacity values must be monotonic (Capacity 1 >  
OCV Cell Model  
Capacity 0, Capacity 2 > Capacity 1, etc.), but other-  
The OCV cell model is a 9-point piece-wise linear  
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.  
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.  
Voltage breakpoints require 2 bytes per breakpoint, but  
are otherwise stored in a similar manner: voltage break-  
point 0: MSB stored at address 68h, LSB stored at  
address 69h. Other voltage breakpoints are stored  
sequentially through address location 79h. Each volt-  
age breakpoint has a resolution of 1.22mV, and a range  
from 0.0V to 4.996V. Voltage breakpoint values must  
also be monotonic. Figure 17 is the Voltage Breakpoint  
Register format.  
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.  
4.2  
BREAKPOINT 7  
4.087V  
90.5%  
4.0  
BREAKPOINT 4  
3.831V  
BREAKPOINT 2  
52.5%  
3.673V  
10%  
3.8  
BREAKPOINT 8  
4.171V  
100%  
BREAKPOINT 6  
BREAKPOINT 5  
3.6  
4.042V  
4.005V  
85%  
80%  
BREAKPOINT 3  
3.752V  
25%  
BREAKPOINT 1  
3.4  
3.619V  
5%  
3.2  
BREAKPOINT 0  
3.186V  
0%  
3.0  
100%  
80%  
60%  
40%  
20%  
0%  
Figure 15. DS2786BG-C3 OCV Cell Model  
ADDRESS 61h–67h  
24 23  
27  
26  
25  
22  
21  
20  
MSB  
LSB  
UNITS: 0.5%  
Figure 16. Capacity 1 to Capacity 7 Registers Format  
______________________________________________________________________________________ 1±  
Stand-Alone OCV-Based Fuel Gauge  
MSB—EVEN ADDRESSES 68h–78h  
29 28 27 26  
LSB—ODD ADDRESS 69h–79h  
21 20  
211  
210  
25  
24  
23  
22  
X
X
X
X
MSB  
LSB  
MSB  
LSB  
“X”: RESERVED  
UNITS: 1.22mV  
Figure 17. Voltage Breakpoint Register Format  
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.  
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.  
Example: Assuming a 15mΩ sense 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%.  
New Capacity Learning  
As the cell ages, the Initial Capacity Scaling Factor  
Register value might no longer accurately reflect the  
true capacity of the cell, causing error in relative capaci-  
ty calculation while in coulomb-counting mode of opera-  
tion. The DS2786B has a learn feature that allows the IC  
to remain accurate as the cell changes. The DS2786B  
MSB—ADDRESS 14h  
LSB—ADDRESS 15h  
S
211  
210  
29  
28  
27  
26  
25  
24  
23  
22  
21  
20  
X
X
X
MSB  
LSB  
MSB  
LSB  
“S”: SIGN BIT(S), “X”: RESERVED  
UNITS: 1.22mV  
Figure 18. Initial Voltage Register Format  
ADDRESS 16h  
24 23  
27  
26  
25  
22  
21  
20  
MSB  
LSB  
UNITS: 0.5%  
Figure 19. Last OCV Register Format  
14 ______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
always read the MSB and the LSB of a 2-byte register  
ADDRESS 7Eh  
24 23  
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.  
27  
26  
25  
22  
21  
20  
MSB  
LSB  
UNITS: 0.5%  
Figure 20. Learn Delta Percent Threshold  
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.  
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  
V
pin prior to writing the COPY bit. The DS2786B  
PROG  
requires the COPY bit be reset to zero within the t  
PROG  
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.  
Memory Map  
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.  
The DS2786B has memory space with registers for instru-  
mentation, status, and control. When the MSB of a 2-byte  
register is read, both the MSB and LSB are latched and  
held for the duration of the read data command to pre-  
vent updates during the read and ensure synchronization  
between the 2 register bytes. For consistent results,  
COPY  
EEPROM  
WRITE  
RECALL  
SERIAL  
INTERFACE  
SHADOW  
READ  
Figure 21. EEPROM Access Through Shadow RAM  
______________________________________________________________________________________ 15  
Stand-Alone OCV-Based Fuel Gauge  
Table ±. Memory Map  
ADDRESS  
0Fh  
DESCRIPTION  
Current Register LSB  
Reserved  
READ/WRITE  
ADDRESS  
00h  
DESCRIPTION  
Reserved  
READ/WRITE  
R
R
R/W  
R
10h to 13h  
14h  
01h  
Status/Config Register  
Relative Capacity  
Reserved  
Initial Voltage MSB  
Initial Voltage LSB  
02h  
15h  
R
03h to 07h  
08h  
R
Auxiliary Input 0 MSB  
Auxiliary Input 0 LSB  
Last OCV Relative  
Capacity  
DS2786B  
16h  
17h  
R
R
09h  
R
Learned Capacity  
Scaling Factor  
Auxiliary Input 1/  
Temperature MSB  
0Ah  
0Bh  
R
R
18h to 5Fh  
60h to 7Fh  
80h to FDh  
FEh  
Reserved  
R/W  
Auxiliary Input 1/  
Temperature LSB  
Parameter EEPROM  
Reserved  
0Ch  
0Dh  
0Eh  
Voltage Register MSB  
Voltage Register LSB  
Current Register MSB  
R
R
R
Command  
R/W  
FFh  
Reserved  
Table 4. Parameter EEPROM Memory Block  
FACTORY  
VALUE  
FACTORY  
VALUE  
ADDRESSS  
DESCRIPTION  
ADDRESS  
DESCRIPTION  
60h  
61h  
62h  
63h  
64h  
65h  
66h  
67h  
68h  
69h  
6Ah  
6Bh  
6Ch  
6Dh  
6Eh  
6Fh  
Current Offset Bias Register  
Capacity 1  
00h  
0Ah  
14h  
32h  
69h  
A0h  
AAh  
B5h  
A3h  
20h  
B9h  
50h  
BCh  
10h  
C0h  
20h  
70h  
71h  
72h  
73h  
74h  
75h  
76h  
77h  
78h  
79h  
7Ah  
7Bh  
7Ch  
7Dh  
7Eh  
7Fh  
Voltage Breakpoint 4 MSB  
Voltage Breakpoint 4 LSB  
Voltage Breakpoint 5 MSB  
Voltage Breakpoint 5 LSB  
Voltage Breakpoint 6 MSB  
Voltage Breakpoint 6 LSB  
Voltage Breakpoint 7 MSB  
Voltage Breakpoint 7 LSB  
Voltage Breakpoint 8 MSB  
Voltage Breakpoint 8 LSB  
Initial Capacity Scaling  
C4h  
20h  
CDh  
10h  
CEh  
F0h  
D1h  
40h  
D5h  
90h  
80h  
06h  
94h  
60h*  
78h  
00h  
Capacity 2  
Capacity 3  
Capacity 4  
Capacity 5  
Capacity 6  
Capacity 7  
Voltage Breakpoint 0 MSB  
Voltage Breakpoint 0 LSB  
Voltage Breakpoint 1 MSB  
Voltage Breakpoint 1 LSB  
Voltage Breakpoint 2 MSB  
Voltage Breakpoint 2 LSB  
Voltage Breakpoint 3 MSB  
Voltage Breakpoint 3 LSB  
OCV Current Threshold  
OCV dV/dt Threshold  
2
I C Address Configuration*  
Learn Threshold  
User EEPROM  
*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  
2
I C Address Configuration Register as illustrated in Figures 24 and 25.  
16 ______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
VOꢁIS—V  
disable. A value of 1 disables the  
OUT  
Status/Config Register  
V
output. When set to zero, this output is driven  
before the AIN0 conversion begins, and dis-  
OUT  
PRE  
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:  
t
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 V  
timeslot. A value of zero restores the measurement  
of AIN1 and enables V during the AIN1 timeslot.  
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.  
is not enabled during the AIN1  
OUT  
OUT  
This bit is EEPROM backed by bit 4 of memory  
location 7Ch. The factory-programmed value is 1.  
SMOꢁ—Sleep Mode enable. A value of 1 allows the  
IC to enter Sleep Mode when SCL and SDA are low  
AIN1—AIN1 conversion valid. This read-only bit  
indicates that the V  
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.  
output was enabled and a  
OUT  
for t  
. A value of zero disables the transition to  
SLEEP  
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.  
AINꢀ—AIN0 conversion valid. This read-only bit  
indicates that the V  
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.  
output was enabled and a  
OUT  
Command Register  
LꢁIS—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.  
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  
X
BIT 6  
PORF  
BIT 5  
BIT 4  
BIT 3  
BIT 2  
BIT 1  
AIN1  
BIT 0  
AIN0  
SMOD  
LDIS  
VODIS  
ITEMP  
X—Reserved.  
Figure 22. Status/Config Register Format  
ADDRESS FEh  
BIT 7  
POR  
BIT 6  
1
BIT 5  
X
BIT 4  
X
BIT 3  
POCV  
BIT 2  
SOCV  
BIT 1  
BIT 0  
COPY  
RCALL  
1—Bit always reads logic 1.  
X—Reserved.  
Figure 23. Command Register Format  
______________________________________________________________________________________ 17  
Stand-Alone OCV-Based Fuel Gauge  
COPY—The Copy bit is set to start a copy command  
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.  
of the scratchpad to EEPROM. A programming volt-  
age must be present on the V  
pin prior for the  
PROG  
copy to be successful. The Copy bit must be cleared  
by software within the t time window.  
PROG  
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.  
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.  
DS2786B  
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.  
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.  
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.  
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.  
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.  
1ꢂ ______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
Slave Address  
A bus master initiates communication with a slave  
device by issuing a START condition followed by a  
slave address (SAddr) and the read/write (R/W) bit.  
When the bus is idle, the DS2786B continuously moni-  
tors for a START condition followed by its slave  
address. When the IC receives an address that match-  
es its slave address, it responds with an Acknowledge  
bit during the clock period following the R/W bit. The  
DS2786BG-C3 7-bit slave address is 0110110. The  
upper 3 bits are fixed at 011; the lower 4 bits can be  
changed by writing the I2C Address Configuration  
Register at location 7Dh.  
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.  
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.  
ADDRESS 7Dh  
BIT 7  
BIT 6  
BIT 5  
BIT 4  
ADDR0  
BIT 3  
X
BIT 2  
X
BIT 1  
X
BIT 0  
X
ADDR3  
ADDR2  
ADDR1  
X—RESERVED.  
2
ADDR3:0—USER-ADJUSTABLE BITS OF THE DS2786BG-C3’S I C ADDRESS. FACTORY DEFAULT IS 0110.  
2
Figure 24. I C Address Configuration Register Format  
BIT 7  
0
BIT 6  
1
BIT 5  
1
BIT 4  
BIT 3  
BIT 2  
BIT 1  
BIT 0  
R/W  
ADDR3  
ADDR2  
ADDR1  
ADDR0  
2
Figure 25. DS2786B I C Address Byte Format  
Table 5. 2-Wire Protocol Key  
KEY  
DESCRIPTION  
KEY  
Sr  
DESCRIPTION  
S
START bit  
Repeated START  
R/W bit = 0  
R/W bit = 1  
STOP bit  
SAddr  
FCmd  
MAddr  
Data  
A
Slave address (7 bit)  
W
Function command byte  
Memory address byte  
R
P
Data byte written by master  
Acknowledge bit—master  
No acknowledge—master  
Data  
A
Data byte returned by slave  
Acknowledge bit—slave  
No acknowledge—slave  
N
N
______________________________________________________________________________________ 19  
Stand-Alone OCV-Based Fuel Gauge  
1 can be written immediately after the acknowledgment  
Basic Transaction Formats  
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.  
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.  
Read: SAddr W A MAddr A Sr SAddr R A Data0 N P  
DS2786B  
Write Portion  
Read Portion  
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.  
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.  
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:  
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.  
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 +  
PACKAGE TYPE PACKAGE COꢁE ꢁOCUMENT NO.  
10 TDFN  
T1033+1  
21-ꢀ1±7  
2ꢀ ______________________________________________________________________________________  
Stand-Alone OCV-Based Fuel Gauge  
DS2786B  
Revision History  
REVISION REVISION  
PAGES  
DESCRIPTION  
CHANGED  
NUMBER  
DATE  
0
7/08  
Initial release  
Changed the maximum operating voltage on V to 4.5V in the Features, Electrical  
Characteristics, and Pin Description sections  
DD  
1
4/10  
1–4  
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are  
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.  
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21  
© 2010 Maxim Integrated Products  
Maxim is a registered trademark of Maxim Integrated Products, Inc.  

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