BQ27620-G1 Datasheet, PDF (26/45 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27620-G1
SLUSAE3 – OCTOBER 2012
5 FUNCTIONAL DESCRIPTION
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5.1 FUEL GAUGING
The bq27620-G1 measures cell voltage and temperature to determine battery SOC. Current is not directly
measured but is estimated by the Impedance Track™ with Dynamic Voltage Correlation (DVC) algorithm.
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 battery impedance determine chemical state of charge. The bq27620-G1
acquires and updates the battery-impedance profile during normal battery usage 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 bq27620-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 Set Threshold. All units are in mAh.
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 [SYSDOWM] flag has already been set,
the [SYSDOWN] flag is cleared. The SOC_INT also signals such change. All units are in mV.
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FUNCTIONAL DESCRIPTION
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