BQ2085 Datasheet, PDF (10/56 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

bq2085
SLUS541 – OCTOBER 2002
RemainingCapacity( ) (RM)
RM represents the remaining capacity in the battery. The bq2085 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 FCC and down during discharge and self-discharge to a
minimum of 0. In addition to charge and self-discharge compensation, the bq2085 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 0x31-0x32 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 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 bq2085 sets FCC to the value stored in Last Measured
Discharge DF 0x35-0x36. During subsequent discharges, the bq2085 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 bq2085 writes the new FCC value to data flash
in mAh to Last Measured Discharge. FCC represents the full battery reference for the relative display mode and
relative state of charge 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 increment. The bq2085 initializes DCR, at the beginning of a discharge, to FCC
– RM when RM is within the programmed value in Near Full DF 0x2f. The DCR initial value of FCC – RM is
reduced by FCC/128 if SC = 0 (bit 5 in Gauge Configuration) and is not reduced if SC = 1. DCR stops counting
when the battery voltage reaches the EDV2 threshold on discharge.
Capacity learning (FCC Update) and Qualified Discharge
The bq2085 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 Battery Low%)
(1)
Battery Low % = (value stored in DF 0x2e) ÷ 2.56
A qualified discharge occurs if the battery discharges from RM ≥ FCC – Near Full to the EDV2 voltage threshold
with the following conditions:
D No valid charge activity occurs during the discharge period. A valid charge is defined as a charge of 10 mAh
into the battery.
D No more than 256 mAh of self-discharge or battery load estimation occurs during the discharge period.
D The temperature does not drop below the low temperature thresholds programmed in Learning Low Temp
DF 0x9b during the discharge period.
D 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 bq2085 detected EDV2.
D No midrange voltage correction occurs during the discharge period.
D Current remains ≥ 3C/32 when EDV2 or Battery Low % level is reached.
D No overload condition exists when EDV2 threshold is reached or if RM( ) has dropped to Battery Low%
*^FCC.
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