BQ27505-J3 Datasheet, PDF (8/44 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27505-J3
Not Recommended for New Designs
SLUS986A – OCTOBER 2009 – REVISED FEBRUARY 2010
www.ti.com
4 GENERAL DESCRIPTION
The bq27505 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 time-to-empty (TTE), time-to-full (TTF) and state-of-charge (SOC) as well as SOC interrupt signal to the
host.
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 bq27505 control and
status registers, as well as its data flash locations. Commands are sent from system to gauge using the
bq27505’s I²C serial communications engine, and can be executed during application development, pack
manufacture, or end-equipment operation.
Cell information is stored in the bq27505 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 bq27505’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 bq27505 provides two 32-byte user-programmable data flash memory blocks: Manufacturer Info
Block A and Manufacturer Info Block B. This data space is accessed through a data flash interface. For
specifics on accessing the data flash, MANUFACTURER INFORMATION BLOCKS.
The key to the bq27505’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 bq27505 measures charge/discharge activity by monitoring the voltage across a small-value series
sense resistor (5 mΩ to 20 mΩ typ.) located between the system’s Vss and the battery’s PACK- terminal.
When a cell is attached to the bq27505, cell impedance is computed, based on cell current, cell
open-circuit voltage (OCV), and cell voltage under loading conditions.
The bq27505 external temperature sensing is optimized with the use of a high accuracy negative
temperature coefficient (NTC) thermistor with R₂₅ = 10.0kΩ ±1%. B25/85 = 3435K ± 1% (such as Semitec
NTC 103AT). The bq27505 can also be configured to use its internal temperature sensor. When an
external themistor is used, a 18.2k pull up resistor between BT/TOUT and TS pins is also required. The
bq27505 uses temperature to monitor the battery-pack environment, which is used for fuel gauging and
cell protection functionality.
To minimize power consumption, the bq27505 has different power modes: NORMAL, SLEEP, SLEEP+,
HIBERNATE, and BAT INSERT CHECK. The bq27505 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 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: brackets and italics, e.g., [TDA]
Data flash bits: brackets, italics and bold, e.g., [LED1]
Modes and states: ALL CAPITALS, e.g., UNSEALED mode.
8
GENERAL DESCRIPTION
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