BQ27741-G1_14 Datasheet, PDF (12/39 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge with Integrated Protection

bq27741-G1
SLUSBF2 – JULY 2013
www.ti.com
FEATURE SET
The bq27741-G1 fuel gauge accurately predicts the battery capacity and other operational characteristics of a
single Li-based rechargeable cell. It can be interrogated by a system processor to provide cell information, such
as state-of-charge (SOC), time-to-empty (TTE), and time-to-full (TTF).
Configuration
Cell information is stored in the fuel gauge in non-volatile flash memory. Many of these data flash locations are
accessible during application development. They cannot, generally, be accessed directly during end-equipment
operation. Access to these locations is achieved by either use of the companion evaluation software, through
individual commands, or through a sequence of data-flash-access commands. To access a desired data flash
location, the correct data flash subclass and offset must be known.
The fuel gauge provides 96 bytes of user-programmable data flash memory, partitioned into three 32-byte
blocks: Manufacturer Info Block A and Manufacturer Info Block B. This data space is accessed through a
data flash interface.
Fuel Gauging
The key to the high-accuracy gas gauging prediction is Texas Instruments proprietary Impedance Track™
algorithm. This algorithm uses cell measurements, characteristics, and properties to create state-of-charge
predictions that can achieve less than 1% error across a wide variety of operating conditions and over the
lifetime of the battery.
See application note SLUA364B, Theory and Implementation of Impedance Track Battery Fuel-Gauging
Algorithm, for further details.
Power Modes
To minimize power consumption, the fuel gauge has different power modes: NORMAL, SLEEP, and
FULLSLEEP. The fuel gauge passes automatically between these modes, depending upon the occurrence of
specific events, though a system processor can initiate some of these modes directly.
NORMAL Mode
The fuel gauge is in NORMAL mode when not in any other power mode. During this mode, AverageCurrent( ),
Voltage( ), and Temperature( ) measurements are taken, and the interface data set is updated. Decisions to
change states are also made. This mode is exited by activating a different power mode.
Because the fuel gauge consumes the most power in NORMAL mode, the Impedance Track™ algorithm
minimizes the time the fuel gauge remains in this mode.
SLEEP Mode
SLEEP mode performs AverageCurrent(), Voltage(), and Temperature() less frequently which results in reduced
power consumption. SLEEP mode is entered automatically if the feature is enabled (Pack Configuration
[SLEEP] = 1) and AverageCurrent( ) is below the programmable level Sleep Current. Once entry into SLEEP
mode has been qualified, but prior to entering it, the fuel gauge performs an ADC autocalibration to minimize
offset.
During the SLEEP mode, the fuel gauge periodically takes data measurements and updates its data set.
However, a majority of its time is spent in an idle condition.
The fuel gauge exits SLEEP if any entry condition is broken, specifically when either:
• AverageCurrent( ) rises above Sleep Current, or
• A current in excess of I_WAKE through R_SENSE is detected.
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