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DS2786B Schematic ( PDF Datasheet ) - Maxim Integrated Products

Teilenummer DS2786B
Beschreibung Stand-Alone OCV-Based Fuel Gauge
Hersteller Maxim Integrated Products
Logo Maxim Integrated Products Logo 




Gesamt 21 Seiten
DS2786B Datasheet, Funktion
19-5223; Rev 1; 4/10
www.DataSheet4U.com
Stand-Alone OCV-Based Fuel Gauge
General Description
The DS2786B estimates available capacity for recharge-
able Li-ion (Li+) and Li+ polymer batteries based on the
cell voltage in the open-circuit state following a relax-
ation period. The open-circuit voltage (OCV) is used to
determine relative cell capacity based on a lookup table
stored in the IC. This capability makes accurate capacity
information available immediately after a battery pack is
inserted. During periods of moderate to high rate dis-
charging, which preclude OCV measurements, the
DS2786B uses coulomb counting as a secondary
means of estimating relative capacity.
Remaining capacity is reported in percent, along with
cell voltage, current, and temperature information. Cell
characteristics and application parameters used in the
calculations are stored in on-chip EEPROM.
The DS2786B is intended for use on the host side of
portable devices, though it can also be mounted within a
battery pack. Measurement and estimated capacity data
are accessed through an I2C interface. Temperature
data is available from an on-die sensor. Resistance mea-
surements of a pack identification resistor and pack ther-
mistor are supported by ratiometric measurements on
two auxiliary inputs.
The DS2786B comes in a 10-pin, lead-free, TDFN 3mm
x 3mm package with an exposed pad (EP).
Applications
3G Multimedia Wireless Handsets
Digital Still Cameras
Digital Audio (MP3) Players
Features
Relative Capacity Calculated from Combination
Coulomb Counter and Open-Circuit Cell Voltage
(OCV) Battery Model
Accurate Warning of Low-Battery Conditions
Even on First Cycle (No Learn Cycle Needed)
12-Bit Battery Voltage Measurement
±10mV Accuracy
1.22mV LSB, 0V to 4.5V Input Range
11-Bit Bidirectional Current Measurement
25µV LSB, ±51.2mV Dynamic Range
1.67mA LSB, ±3.4A (RSNS = 15mΩ)
Current Accumulation Measurement Resolution
±204.8mVh Range
±13.65Ah (RSNS = 15mΩ)
Internal Temperature Measurement
0.125°C LSB, ±3°C Accuracy
Two 11-Bit Auxiliary Input-Voltage Measurements
±8 LSB Accuracy, Ratiometric Inputs Eliminate
Supply Accuracy Issues
VOUT Pin Drives Resistive Dividers, Reduces
Current Consumption
2-Wire Interface
Low Power Consumption
Active Current: 50µA (typ), 80µA (max)
Sleep Current: 1µA (typ), 3µA (max)
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
DS2786BG+
-20°C to +70°C 10 TDFN-EP*
DS2786BG+T&R
-20°C to +70°C 10 TDFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
T&R = Tape and reel.
Operating Diagram
Li+
PROTECTION
CIRCUIT
VOUT
VIN
DS2786B
AIN0
AIN1
VSS
SDA
SCL
SNS
SYSTEM
μP
I2C
INTERFACE
RSNS
(EEPROM PROGRAMMING TEST POINT NOT SHOWN)
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.






DS2786B Datasheet, Funktion
Stand-Alone OCV-Based Fuel Gauge
www.DataSheet4U.com
Detailed Description
The DS2786B provides current-flow, voltage, and
temperature-measurement data to support battery-
capacity monitoring in cost-sensitive applications.
Current is measured bidirectionally over a dynamic
range of ±51.2mV with a resolution of 25µV. Assuming
a 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
magnitude in the 2-byte Current Register. Battery-
voltage measurements are reported in the 2-byte
Voltage Register with 12-bit (1.22mV) resolution, and
auxiliary voltage measurements are reported in the 2-
byte Aux Volt Registers with 11-bit resolution.
Additionally, the Temperature Register reports tempera-
ture with 0.125°C resolution and ±3°C accuracy from
the on-chip sensor. The on-chip temperature measure-
ment is optional and replaces auxiliary voltage channel
AIN1. Figure 1 is the 2-wire bus timing diagram; Figure
2 is the DS2786B block diagram. Figure 3 is an appli-
cation example.
VOUT
TEMPERATURE
MEASUREMENT
AIN1
Figure 2. Block Diagram
SWITCH IS ON WHEN AIN0 OR AIN1 IS BEING MEASURED.
BIAS TIMEBASE
VOLTAGE
REFERENCE
ADC
STATE
MACHINE
EEPROM
2-WIRE
INTERFACE
1kΩ
VDD
VPROG
SDA
SCL
SNS
VIN AIN0
1kΩ
VSS
IC
GROUND
6 _______________________________________________________________________________________

6 Page









DS2786B pdf, datenblatt
Stand-Alone OCV-Based Fuel Gauge
www.DataSheet4U.com
Prior to the first learn operation, the relative capacity
value is calculated by adding the IACR multiplied by the
initial capacity scaling factor (7Ah) to the last OCV rela-
tive capacity (16h). After the first learn operation, the rel-
ative capacity value is calculated by adding the IACR
multiplied by the learned capacity scaling factor (17h) to
the last OCV relative capacity (16h).
Each Capacity Scaling Factor Register has a resolution
of 78.125%/Vh and a maximum range of 0 to
19921.875%/Vh. During assembly, the Initial Capacity
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.
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
27 26 25 24 23 22 21 20
MSB
LSB
UNITS: 78.125%/Vh
Figure 11. Initial Capacity Scaling Factor Register Format
operational current, but above the maximum idle cur-
rent of the application should be selected. The OCV
Threshold Register has a resolution of 25µV/RSNS, and
a range from 0mV/RSNS to 6.375mV/RSNS. The factory
default value is 28h. See Figure 13 for the OCV thresh-
old register format.
While the measured current is below the OCV threshold
level, the DS2786B actively searches for a relaxed cell
by calculating the change in cell voltage as reported in
the Voltage Register over 7.5min intervals (dV/dt). If the
7.5min dV/dt change of an average of four Voltage
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.
The OCV dV/dt Threshold Register has a resolution of
0.61mV/7.5min and a range from 0mV/7.5min to
9.15mV/7.5min. The factory default value is
2.44mV/7.5min. Note that the upper 4 bits of the OCV
dV/dt Threshold Register are used to EEPROM back
bits from the Status/Configuration Register. Figure 14
shows the OCV dV/dt threshold register format.
ADDRESS 7Bh
27 26 25 24 23 22 21 20
MSB
LSB
UNITS: 25μV/RSNS
Figure 13. OCV Threshold Register Format
ADDRESS 17h
27 26 25 24 23 22 21 20
MSB
LSB
UNITS: 78.125%/Vh
Figure 12. Learned Capacity Scaling Factor Register Format
ADDRESS 7Ch
SMOD LDIS VODIS ITEMP 23 22 21 20
MSB
LSB
UNITS: 0.61mV/7.5min
Figure 14. OCV dV/dt Threshold Register Format
12 ______________________________________________________________________________________

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