SCL

SRX

VSYS

Coulomb

Bus

SDA

Counter

GPOUT

BIN

CPU

ADC

PACKP

Li-Ion

Cell

LDO

VDD

VSS

T

PACKN

Protection

IC

NFET NFET

1.8 V

BAT

BatteryPack

047 µF

.

1 µF

Integrated

Sense

Resistor

bq27421-G1

www.ti.com

SLUSB85E – MAY 2013 – REVISED JANUARY 2016

8 Detailed Description

8.1 Overview

The 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).

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

8.2 Functional Block Diagram

8.3 Feature Description

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

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 fuel gauge measures the charging and discharging of the battery by monitoring the voltage across a small-

value sense resistor. 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 fuel gauge uses an integrated temperature sensor for estimating cell temperature. Alternatively, the host

processor can provide temperature data for the fuel gauge.

Copyright © 2013–2016, Texas Instruments Incorporated

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