BQ27350 Datasheet, PDF (7/33 Pages) Texas Instruments – Single Cell Li-Ion Battery Manager With Impedance Track Fuel Gauge Technology

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4 GENERAL DESCRIPTION
bq27350
Single Cell Li-Ion Battery Manager
With Impedance Track Fuel Gauge Technology
SLUS754 – MARCH 2007
The bq27350 accurately predicts the battery capacity and other operational characteristics of a single
Li-based rechargeable cell. It can be interrogated by a host 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 bq27350’s control and
status registers, as well as its data flash locations. Commands are sent from host to gauge using the
bq27350’s I²C engine, and can be executed during application development, pack manufacture, or
end-equipment operation.
Cell information is stored inside the bq27350 in non-volatile flash memory. Many of these data flash
locations are accessible during application development and pack manufacture. They cannot, generally,
be accessed directly during end-equipment operation. Access to these locations is achieved by either use
of the bq27350’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 bq27350 provides 96 bytes of user-programmable data flash memory, partitioned into 3 32-byte
blocks: Manufacturer Info A,Manufacturer Info B, and Manufacturer Info C. This data space is
accessed through a data flash interface. For specifics on accessing the data flash, refer to the section
entitled DATA FLASH INTERFACE.
The key to the bq27350’s high-accuracy gas gauging prediction is Texas Instrument’s proprietary
Impedance Track™ algorithm. This algorithm combines cell measurements, characteristics, and properties
to create state-of-charge predictions that can achieve better than 1% accuracy across a wide variety of
operating conditions.
The bq27350 measures charge/discharge activity by monitoring the voltage across a small-value series
sense resistor (5 mΩ to 20 mΩ typical) between the cell negative terminal and the low-side protection
FETs. When an application’s load is applied, cell impedance is measured by comparing its Open Circuit
Voltage (OCV) with its measured voltage under loading conditions.
The bq27350 can use an external NTC thermistor (default is Semitec 103AT) for temperature
measurement, or can also be configured to use its internal temperature sensor. The bq27350 uses
temperature to monitor the battery-pack environment, which is used for fuel gauging and cell protection
functionality.
To minimize power consumption, the bq27350 has several power modes: NORMAL, SLEEP,
HIBERNATE, and SHUTDOWN. The bq27350 passes automatically between these modes, depending
upon the occurrence of specific events, though a host processor can initiate some of these modes directly.
More details can be found in the section entitled POWER MODES.
A battery-pack-authentication feature is also implemented on the bq27350. A scratch pad area is used to
both receive challenge information from a host and export SHA-1/HMAC encrypted responses. The
bq27350 can perform the encryption directly, or can act as a pass-through to a bq26100 stand-alone
authentication IC. Specifics can be found in the section entitled AUTHENTICATION.
FORMATTING CONVENTIONS:
NOTE
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: brackets only, e.g. [TDA]
Modes and states: ALL CAPITALS, e.g. UNSEALED mode.
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GENERAL DESCRIPTION
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