BQ27425-G2_15 Datasheet, PDF (9/39 Pages) Texas Instruments – Fuel Gauge With Integrated Sense Resistor

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8 Detailed Description
bq27425-G2
SLUSB23B – OCTOBER 2012 – REVISED JUNE 2015
8.1 Overview
The bq27425 device accurately predicts the battery capacity and other operational characteristics of a single Li-
based rechargeable cell. The device can be interrogated by a system processor to provide cell information, such
as state-of-charge (SOC).
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 control and status registers, as well as
its data locations. Commands are sent from system to gauge using the I²C serial communications engine, and
can be executed during application development, system manufacture, or end-equipment operation.
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 high accuracy across a wide variety of operating conditions and over the lifetime of
the battery.
The bq27425 device measures charging and discharging of the battery by monitoring the voltage across a small-
value integrated sense resistor (10 mΩ, typical) located between the system V_SS and the battery’s PACK–
terminal. When a cell is attached to the fuel gauge, cell impedance is computed, based on cell current, cell open-
circuit voltage (OCV), and cell voltage under loading conditions.
The device uses an integrated temperature sensor for estimating cell temperature. Alternatively, the host
processor can provide temperature data for the fuel gauge.
To minimize power consumption, the fuel gauge has several power modes: INITIALIZATION, NORMAL, SLEEP,
and HIBERNATE. 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. See Operating Modes.
NOTE
The following formatting conventions are used in this document:
Commands: italics with parentheses( ) and no breaking spaces, for example, Control( )
Data Flash: italics, bold, and breaking spaces, for example, Design Capacity
Register bits and flags: italics with brackets [ ], for example, [TDA]
Data Flash bits: italics, bold, and brackets [ ], for example, [LED1]
Modes and states: ALL CAPITALS, for example, UNSEALED mode
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