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bq27530-G1

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SLUSAL5B – DECEMBER 2012 – REVISED JANUARY 2016

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Copyright © 2012–2016, Texas Instruments Incorporated

7.3 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

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

Cell information is stored 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 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 key to the high-accuracy gas gauging prediction is the TI proprietary Impedance Track™ algorithm. This

algorithm uses cell measurements, characteristics, and properties to create SOC predictions that can achieve

less than 1% error 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 series sense resistor (5 to 20 m

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

(NTC) thermistor with R25 = 10.0 k

Ω ±1%, B25/85 = 3435 K ± 1% (such as Semitec NTC 103AT). The fuel

gauge can also be configured to use its internal temperature sensor. When an external thermistor is used, a

18.2-k

Ω pullup resistor between the BI/TOUT and TS pins is also required. The fuel gauge uses temperature to

monitor the battery-pack environment, which is used for fuel gauging and cell protection functionality.

To minimize power consumption, the fuel gauge has different power modes: NORMAL, SLEEP, SLEEP+,

HIBERNATE, and BAT INSERT CHECK. 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.

7.3.1 Functional Description

The fuel gauge measures the cell voltage, temperature, and current to determine battery SOC. The fuel gauge

monitors the charging and discharging of the battery by sensing the voltage across a small-value resistor (5 m

Ω

to 20 m

Ω, typical) between the SRP and SRN pins and in series with the cell. By integrating charge passing

through the battery, the battery SOC is adjusted during battery charge or discharge.

The total battery capacity is found by comparing states of charge before and after applying the load with the

amount of charge passed. When an application load is applied, the impedance of the cell is measured by

comparing the OCV obtained from a predefined function for present SOC with the measured voltage under load.

Measurements of OCV and charge integration determine chemical SOC and chemical capacity (Qmax). The

initial Qmax values are taken from a cell manufacturers' data sheet multiplied by the number of parallel cells. It is

also used for the value in Design Capacity. The fuel gauge acquires and updates the battery-impedance profile

during normal battery usage. It uses this profile, along with SOC and the Qmax value, to determine

FullChargeCapacity(

)

and

StateOfCharge(

),

specifically

for

the

present

load

and

temperature.

FullChargeCapacity( ) is reported as capacity available from a fully-charged battery under the present load and

temperature

until

Voltage(

)

reaches

the

Terminate

Voltage.

NominalAvailableCapacity(

)

and

FullAvailableCapacity( ) are the uncompensated (no or light load) versions of RemainingCapacity( ) and

FullChargeCapacity( ), respectively.

The fuel gauge has two flags accessed by the Flags( ) function that warn when the battery SOC has fallen to

critical levels. When RemainingCapacity( ) falls below the first capacity threshold as specified in SOC1 Set

Threshold, the [SOC1] (State of Charge Initial) flag is set. The flag is cleared once RemainingCapacity( ) rises

above SOC1 Clear Threshold.

When the voltage is discharged to Terminate Voltage, the SOC will be set to 0.