BQ27531-G1 Datasheet, PDF (13/21 Pages) Texas Instruments – Battery Management Unit Impedance Track Fuel Gauge for Use With the bq2419x Charger Controller

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FUNCTIONAL DESCRIPTION
bq27531-G1
SLUSBE7 – MARCH 2013
The bq27531-G1 measures the cell voltage, temperature, and current to determine battery SOC. The bq27531-
G1 monitors charge and discharge activity by sensing the voltage across a small-value resistor
(5 mΩ to 20 mΩ typ.) between the SRP and SRN pins and in series with the cell. By integrating charge passing
through the battery, the battery’s 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 state of charge 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 bq27531-G1 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 bq27531-G1 has two flags accessed by the Flags( ) function that warns when the battery’s SOC has fallen
to critical levels. When RemainingCapacity( ) falls below the first capacity threshold, 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 Voltage( ) falls below the system shut down threshold voltage, SysDown Set Volt Threshold, the
[SYSDOWN] flag is set, serving as a final warning to shut down the system. The SOC_INT also signals. When
Voltage( ) rises above SysDown Clear Voltage and the [SYSDOWN] flag has already been set, the
[SYSDOWN] flag is cleared. The SOC_INT also signals such change. All units are in mV.
When the voltage is discharged to Terminate Voltage, the SOC will be set as 0.
Copyright © 2013, Texas Instruments Incorporated
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