19-4637; 5/09
DS2786
Stand-Alone OCV-Based
Fuel Gauge
www.maxim-ic.com
GENERAL DESCRIPTION
The DS2786 estimates available capacity for
rechargeable Li-Ion and Li-Ion Polymer batteries
based on the cell voltage in the open-circuit state
following a relaxation period. The open-circuit voltage
(OCV) is used to determine relative cell capacity
based on a lookup table stored in the IC. This
capability makes accurate capacity information
available immediately after a battery pack is inserted.
During periods of moderate to high rate discharging,
which preclude OCV measurements, the DS2786
uses coulomb counting as a secondary means of
estimating relative capacity.
Remaining capacity is reported in percent, along with
cell voltage, current and temperature information.
Cell characteristics and application parameters used
in the calculations are stored in on-chip EEPROM.
The DS2786 is intended for use on the host side of
portable devices, though it can also be mounted
within a battery pack. Measurement and estimated
2
capacity data are accessed through an I C interface.
Temperature data is available from an on-die sensor.
Resistance measurements of a pack identification
resistor and pack thermistor are supported by
ratiometric measurements on two auxiliary inputs.
FEATURES
Relative Capacity Calculated from
Combination Coulomb Counter and Open-
Circuit Cell Voltage (OCV) Battery Model
Accurate Warning of Low Battery Conditions
Even On First Cycle (No Learn Cycle Needed)
12-Bit Battery Voltage Measurement:
±10mV Accuracy
1.22mV LSB, 0V to 4.5V Input Range
11-Bit Bidirectional Current Measurement:
25V LSB, ±51.2mV Dynamic Range
1.67mA LSB, ±3.4A (R
SNS
= 15m)
Current Accumulation Measurement
Resolution:
±204.8mVh Range
±13.65Ah (R
SNS
= 15m)
Internal Temperature Measurement:
0.125°C LSB, ±3°C Accuracy
Two 11-Bit Aux Input Voltage Measurements:
±8 LSB Accuracy, Ratiometric Inputs
Eliminate Supply Accuracy Issues
V
OUT
Pin Drives Resistive Dividers, Reduces
Current Consumption
2-Wire Interface
Low Power Consumption:
Active Current: 50A typ, 80A max
Sleep Current: 1A typ, 3A max
APPLICATIONS
3G Multimedia Wireless Handsets
Digital Still Cameras
Digital Audio (MP3) Players
ORDERING INFORMATION
PART
DS2786G+
DS2786G+T&R
TEMP RANGE
-20ºC to +70ºC
-20ºC to +70ºC
PIN-PACKAGE
10 TDFN-EP*
10 TDFN-EP*
TYPICAL OPERATING CIRCUIT
+Denotes a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
*EP = Exposed pad.
PIN CONFIGURATION
Commands, Registers, and Modes are capitalized for clarity.
3mm x 3mm TDFN-10
Top View
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DS2786 Stand-Alone OCV-Based Fuel Gauge
ABSOLUTE MAXIMUM RATINGS
Voltage Range on All Pins Except V
PROG
Relative to V
SS
Voltage Range on V
PROG
Relative to V
SS
Operating Temperature Range
Storage Temperature Range
Soldering Temperature
-0.3V to +6V
-0.3V to +18V
-40°C to +85°C
-55°C to +125°C
Refer to the IPC/JEDECJ-STD-020 Specification.
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the
operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of
time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
(2.5V
V
DD
4.5V, T
A
= -20C to +70C.)
PARAMETER
Supply Voltage
Data I/O Pins
Programming Pin
VIN, AIN0, AIN1 Pin
SYMBOL
V
DD
SCL, SDA
V
PROG
V
IN
, AIN0,
AIN1
CONDITIONS
(Note 1)
(Note 1)
(Note 1)
(Note 1)
MIN
+2.5
-0.3
-0.3
-0.3
TYP
MAX
+4.5
+4.5
+15.5
V
DD
+ 0.3
UNITS
V
V
V
V
DC ELECTRICAL CHARACTERISTICS
(2.5V
V
DD
4.5V, T
A
= -20C to +70C, unless otherwise noted.)
PARAMETER
Active Current
SYMBOL
I
ACTIVE
V
DD
= 2.0V,
SCL, SDA = V
SS
SCL, SDA = V
SS
Current Measurement
Resolution
Current Measurement
Full-Scale Magnitude
Current Measurement
Offset Error
Current Measurement
Gain Error
I
LSB
I
FS
I
OERR
I
GERR
V
DD
= 3.6V at +25°C
Timebase Accuracy
t
ERR
T
A
= 0C to +70C
T
A
= -20C to +70C
Voltage Error
Input Resistance
VIN, AIN0, AIN1
AIN0, AIN1 Error
V
OUT
Output Drive
I
O
= 1mA
V
GERR
V
DD
= V
IN
= 3.6V,
T
A
= 0C to +50C
T
A
= -20C to +70C
R
IN
DS2786
(Note 1)
DS2786 (Note 2)
-50
-1.5
-1
-2
-3
-10
-20
15
-8
V
DD
- 0.5
+8
CONDITIONS
MIN
TYP
50
0.3
1
25
±51.2
+50
+1.5
+1
+2
+3
+10
mV
+20
MΩ
LSB
V
%
MAX
75
UNITS
A
1.0
3
Sleep-Mode Current
I
SLEEP
A
V
mV
V
% of
reading
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DS2786 Stand-Alone OCV-Based Fuel Gauge
PARAMETER
Spike Pulse Widths
Suppressed by Input
Filter
Capacitive Load for Each
Bus Line
SCL, SDA Input
Capacitance
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
SYMBOL
t
SP
C
B
C
BIN
CONDITIONS
(Note 8)
(Note 9)
MIN
0
TYP
MAX
50
400
60
UNITS
ns
pF
pF
All voltages are referenced to V
SS
.
Offset specified after auto-calibration cycle and Current Offset Bias Register = 00h.
The DS2786 enters the Sleep mode 1.5s to 2.2s after (SCL < V
IL
) AND (SDA < V
IL
).
Timing must be fast enough to prevent the DS2786 from entering Sleep mode due to bus low for period
> t
SLEEP
.
f
SCL
must meet the minimum clock low time plus the rise/fall times.
The maximum t
HD:DAT
has only to be met if the device does not stretch the LOW period (t
LOW
) of the SCL
signal.
This device internally provides a hold time of at least 100ns for the SDA signal (referred to the V
IHmin
of
the SCL signal) to bridge the undefined region of the falling edge of SCL.
Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant.
C
B
—total capacitance of one bus line in pF.
Figure 1. 2-Wire Bus Timing Diagram
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DS2786 Stand-Alone OCV-Based Fuel Gauge
PIN DESCRIPTION
PIN
1
2
3
4
5
6
7
8
9
10
PAD
NAME
AIN1
AIN0
SCL
SDA
SNS
V
SS
V
PROG
V
OUT
V
IN
V
DD
PAD
FUNCTION
Aux Voltage Input Number 1
Aux Voltage Input Number 0
Serial Clock Input.
Input only 2-wire clock line. Connect this pin to the clock signal of the
2-wire interface. This pin has a 0.2µA typical pulldown to sense disconnection.
Serial Data Input/Output.
Open drain 2-wire data line. Connect this pin to the clock
signal of the 2-wire interface. This pin has a 0.2µA typical pulldown to sense
disconnection.
Current-Sense Input.
Connect to the handset side of the sense resistor.
Device Ground.
Connect to the battery side of the sense resistor.
EEPROM Programming Voltage Input.
Connect to external supply for production
programming. Connect to V
SS
during normal operation.
Voltage Out.
Supply for Aux Input Voltage Measurement Dividers. Connect to high side
of resistor divider circuits.
Battery Voltage Input.
The voltage of the cell pack is measured through this pin.
Power-Supply Input.
2.5V to 4.5V input range. Connect to system power through a
decoupling network.
Exposed Pad.
Connect to V
SS
.
Figure 2. Block Diagram
VIN
AIN0
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PCB Design
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