BQ2084-V140_14 Datasheet, PDF (10/64 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE FOR USE WITH THE bq29312

bq2084-V140
SLUS664B – JULY 2005 – REVISED AUGUST 2006
www.ti.com
The FullChargeCapacity() (FCC) register represents the last measured learned full discharge of the battery. It is
used as the battery full-charge reference for relative capacity indication. The bq2084-V140 updates FCC after
the battery undergoes a qualified discharge from nearly full to a low battery level. FCC is accessible through the
SMBus interface.
The Discharge Count Register (DCR) is a non-accessible register that tracks discharge of the battery. The
bq2084-V140 uses the DCR register to update the FCC register if the battery undergoes a qualified discharge
from nearly full to a low battery level. In this way, the bq2084-V140 learns the true discharge capacity of the
battery under system-use conditions.
Main Gas-Gauge Registers
RemainingCapacity() (RM)
RM represents the remaining capacity in the battery. The bq2084-V140 computes RM in units of either mAh or
10 mWh depending on the selected mode. See Battery Mode() (0x03) for units configuration. RM counts up
during charge to a maximum value of FullChargeCapacity() (FCC) and down during discharge and
self-discharge to a minimum of 0. In addition to charge and self-discharge compensation, the bq2084-V140
calibrates RM at three low-battery-voltage thresholds, EDV2, EDV1, and EDV0 and three programmable
midrange thresholds VOC25, VOC50, and VOC75. This provides a voltage-based calibration to the RM counter.
DesignCapacity () (DC)
DC is the user-specified battery full capacity. It is calculated from Pack Capacity DF 0x32-0x33 and is
represented in units of mAh or 10 mWh. It also represents the full-battery reference for the absolute display
mode.
FullChargeCapacity() (FCC)
FCC is the last learned measured discharge capacity of the battery. It is represented in units of either mAh or 10
mWh, depending on the selected mode. On initialization, the bq2084-V140 sets FCC to the value stored in Full
Charge Capacity DF 0x36-0x37. During subsequent discharges, the bq2084-V140 updates FCC with the last
learned measured discharge capacity of the battery. The last learned measured discharge of the battery is
based on the value in the Discharge Count Register (DCR) after a qualified discharge occurs. Once updated, the
bq2084-V140 writes the new FCC value to data flash in mAh to Full Charge Capacity. FCC represents the
full-battery reference for the relative display mode, relative state of charge and AtRate() calculations.
Discharge Count Register (DCR)
The DCR register counts up during discharge, independent of RM. DCR counts discharge activity, battery load
estimation, and self-discharge increments. The bq2084-V140 initializes DCR, at the beginning of a discharge, to
FCC - RM when FCC - RM is within the programmed value in Near Full DF 0x30. The DCR initial value of FCC -
RM is reduced by FCC/128 if SC = 1 (bit 5 in Gauge Configuration) and is not reduced if SC = 0. DCR stops
counting when the battery voltage reaches the EDV2 threshold on discharge.
Capacity Learning (FCC Update) and Qualified Discharge
The bq2084-V140 updates FCC with an amount based on the value in DCR if a qualified discharge occurs. The
new value for FCC equals the DCR value plus the programmable nearly full and low battery levels, according to
the following equation:
FCC (new) = DCR (final) = DCR (initial) + Measured Discharge to EDV2 + (FCC x Battery Low%)
here Battery Low % = (value stored in DF 0x2f) ÷ 2.56
A qualified discharge occurs if the battery discharges from RM = FCC - Near Full to the EDV2 voltage threshold
with the following conditions:
• No more than 256 mAh of self-discharge or battery load estimation occurs during the discharge period.
• The temperature does not drop below the low temperature threshold programmed in Learning Low Temp DF
0xac during the discharge period.
• The battery voltage reaches the EDV2 threshold during the discharge period, and the voltage is greater than
or equal to the EDV2 threshold minus 256 mV when the bq2084-V140 detects EDV2.
• No midrange voltage correction occurs during the discharge period.
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