9

bq27320

www.ti.com

SLUSCG9A – FEBRUARY 2016 – REVISED MARCH 2016

Product Folder Links: bq27320

Submit Documentation Feedback

Copyright © 2016, Texas Instruments Incorporated

8 Detailed Description

8.1 Overview

The bq27320 measures the voltage, temperature, and current to determine battery capacity and state of charge

(SOC). The bq27320 monitors charge and discharge activity by sensing the voltage across a small-value resistor

(5 m

Ω to 20 mΩ typical) between the SRP and SRN pins and in series with the battery. By integrating charge

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

Measurements of OCV and charge integration determine chemical state of charge. The 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. It uses the OCV and Qmax value to determine StateOfCharge() on battery insertion, device

reset, or on command. The FullChargeCapacity() is reported as the learned capacity available from full charge

until Voltage() reaches the EDV0 threshold.

As Voltage() falls below the SysDown Set Volt Threshold, the Flags() [SYSDOWN] bit is set and SOC_INT will

toggle once to provide a final warning to shut down the system. As Voltage() rises above SysDown Clear

Voltage the [SYSDOWN] bit is cleared.

Additional details are found in the bq27320 Technical Reference Manual (SLUUBE6).

The fuel gauging is derived from the Compensated End of Discharge Voltage (CEDV) method, which uses a

mathematical model to correlate remaining state of charge (RSOC) and voltage near to the end of discharge

state. This requires a full discharge cycle for a single point FCC update. The implementation models cell voltage

(OCV) as a function of battery state of charge (SOC), temperature, and current. The impedance is also a function

of SOC and temperature, all of which can be satisfied by using seven parameters: EMF, C0, R0, T0, R1, TC, C1.

For more detailed information, contact TI Applications Support at http://www-k.ext.ti.com/sc/technical-

support/email-tech-support.asp?AAP.