General Description; Gas Gauging - Texas Instruments BQ27220 Technical Reference Manual

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User manual (20 pages)

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The BQ27220 fuel gauge, using compensated end-of-discharge voltage (CEDV) technology, accurately predicts

the battery capacity and other operational characteristics of a single series, Li-based rechargeable cell. It can

be interrogated by a system processor to provide cell information such as time-to-empty (TTE), state-of-charge

(SOC), and the 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(), read and write information contained within the device control and status registers, as well as its

data memory locations. Commands are sent from system to gauge using the I

and can be executed during application development, system manufacture, or end-equipment operation.

Cell information is stored in the device in One-Time Programmable (OTP) memory. Many of these data memory

locations are accessible during application development. They cannot, in general, be accessed directly during

end-equipment operation. Access to these locations is achieved by either using the companion evaluation

software, through individual commands, or through a sequence of data-flash–access commands. To access a

desired data memory location, the correct data memory address must be known.

The fuel gauge measures charge and discharge activity by monitoring the voltage across a small-value series

sense resistor (5 mΩ to 20 mΩ, typical) located between the system V

a cell is attached to the device, information is based on cell current, cell open-circuit voltage (OCV), and cell

voltage under loading conditions.

The external temperature sensing is optimized with the use of a high-accuracy negative temperature coefficient

(NTC) thermistor with R25 = 10.0 kΩ ±1%. B25/85 = 3435 kΩ ± 1% (such as Semitec NTC 103AT). Alternatively,

the fuel gauge can be configured to use its internal temperature sensor or receive temperature data from the

host processor. The fuel gauge uses temperature to monitor the battery-pack environment, which is used for gas

gauging and cell protection functionality.

To minimize power consumption, the fuel gauge has several power modes: INITIALIZATION, NORMAL, SLEEP,

and SHUTDOWN. 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.

1.1 Gas Gauging

The BQ27220 device features the Compensated End-of-Discharge Voltage (CEDV) gauging algorithm, capable

of gauging a maximum capacity of 32 Ah.

Figure 1-1

shows the operational overview of the BQ27220 fuel gauge.

SLUUBD4A – APRIL 2016 – REVISED NOVEMBER 2022

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