Introduction
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SLUUBD3D–September 2015–Revised September 2018
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CEDV Gas Gauging
The bq78350-R1 computes RC in units based of the settings of two configuration bits, CapM and
SpecificationInfo(). RC counts up during charge to a maximum value of FCC and down during discharge
and self-discharge to a minimum of 0. In addition to charge and self-discharge compensation, the
bq78350-R1 calibrates RC at three low-battery-voltage thresholds, EDV2, EDV1, and EDV0. This provides
a voltage-based calibration to the RC counter and is based on the lowest voltage measured at the BAT
pin.
The Design Capacity (DC) register is the user-specified battery full capacity. It is calculated from Design
Capacity and is represented in units set by CapM. It also represents the full-battery reference for the
absolute display mode and AbsoluteStateOfCharge(). In programming Design Capacity, the value should
not include the value programmed in Reserve Capacity.
The FullChargeCapacity() (FCC) register represents the initial or last measured full discharge of the
battery. It is used as the battery full-charge reference for relative capacity indication. The bq78350-R1
updates FCC after the battery undergoes a qualified discharge from nearly full to a low battery level. FCC
is accessible through the SMBus.
The bq78350-R1 computes FCC in units based of the settings of two configuration bits, CapM and
IPScale. On initialization, the bq78350-R1 sets FCC to the value stored in Full Charge Capacity. During
subsequent discharges, the bq78350-R1 updates FCC with the last measured discharge capacity of the
battery. The last measured discharge of the battery is based on the value in the DCR register after a
qualified discharge occurs. Once updated, the bq78350-R1 writes the new FCC value to data flash in
mAh, scaled per the setting of IPScale, to Full Charge Capacity.
NOTE: Care should be taken to ensure that the correct scaling is used to ensure that the Full
Charge Capacity does not exceed 65535 of the units configured by the scaling. If Full
Charge Capacity is calculated to be above 65535, then it will roll over creating potentially
uncorrectable error in the gauging algorithm.
9.1.2 Fuel Gauge Operating Modes
During a gauging operation, different features and functions occur based on whether the battery is
discharging, charging, or in a rest state.
Entry and exit of each mode is controlled by data flash parameters in the subclass Fuel Gauging: Current
Thresholds section.
• In RELAX mode or DISCHARGE mode, the [DSG] flag in GaugingStatus() is set.
• CHARGE mode is entered when Current goes above Chg Current Threshold.
• CHARGE mode is exited and RELAX mode is entered when Current goes below Quit Current for a
period of Chg Relax Time.
• DISCHARGE mode is entered when Current goes below (–)Dsg Current Threshold.
• DISCHARGE mode is exited and RELAX mode is entered when Current goes above (–)Quit Current
threshold for a period of Dsg Relax Time.
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