BQ27541 Datasheet, PDF (8/38 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

bq27541
SLUS861 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
GENERAL DESCRIPTION
The bq27541 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).
Information is accessed through a series of commands, called Standard Commands. Further capabilities are
provided by the additional Extended Commands set. Both sets of commands, indicated by the general format
Command( ), are used to read and write information contained within the bq27541 control and status registers,
as well as its data flash locations. Commands are sent from system to gauge using the bq27541’s serial
communications engine, and can be executed during application development, pack manufacture, or
end-equipment operation.
Cell information is stored in the bq27541 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 bq27541’s 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 bq27541 provides 96 bytes of user-programmable data flash memory, partitioned into 3 32-byte blocks:
Manufacturer Info Block A, Manufacturer Info Block B, and Manufacturer Info Block C. This data space is
accessed through a data flash interface. For specifics on accessing the data flash, see section Manufacturer
Information Blocks. The key to the bq27541’s high-accuracy gas gauging prediction is Texas Instrument’s
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.
The bq27541 measures charge/discharge activity by monitoring the voltage across a small-value series sense
resistor (5 mΩ to 20 mΩ typ.) located between the CELL- and the battery’s PACK- terminal. When a cell is
attached to the bq27541, cell impedance is computed, based on cell current, cell open-circuit voltage (OCV), and
cell voltage under loading conditions.
The bq27501 external temperature sensing is optimized with the use of a high accuracy negative temperature
coefficient (NTC) thermistor with R₂₅ = 10KΩ ± 1% and B25/85 = 3435KΩ ± 1% (such as Semitec 103AT for
measurement). The bq27501 can also be configured to use its internal temperature sensor. The bq27541 uses
temperature to monitor the battery-pack environment, which is used for fuel gauging and cell protection
functionality.
To minimize power consumption, the bq27541 has different power modes: NORMAL, SLEEP, FULLSLEEP,
HIBERNATE, and PRESHUTDOWN. The bq27541 passes automatically between these modes, depending upon
the occurrence of specific events, though a system processor can initiate some of these modes directly. More
details can be found in section Power Modes.
NOTE:
FORMATTING CONVENTIONS IN THIS DOCUMENT:
Commands: italics with parentheses( ) and no breaking spaces. e.g. RemainingCapacity( )
Data Flash: italics, bold, and breaking spaces. e.g. Design Capacity
Register bits and flags: italics with brackets[]. e.g. [TDA]
Data flash bits: italics, bold, and brackets[]. e.g: [LED1]
Modes and states: ALL CAPITALS. e.g. UNSEALED mode
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