BQ2084DBTR-V150 Datasheet, PDF (11/69 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE WITH LED DELAY

bq2084-V150
www.ti.com
SLUS758 – JUNE 2007
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-V150 sets FCC to the value stored in Full
Charge Capacity DF 0x36-0x37. During subsequent discharges, the bq2084-V150 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-V150 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-V150 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-V150 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-V150 detects EDV2.
• No midrange voltage correction occurs during the discharge period.
• Current remains ≤ 3C/32 when EDV2 or Battery Low % level is reached.
• No overload condition exists when EDV2 threshold is reached, or if RM() has dropped to Battery Low% x
FCC,
• No valid charge activity occurs during the discharge period. A valid charge is defined as an uninterrupted
charge of 10 mAh into the battery.
The bq2084-V150 sets VDQ = 1 in PackStatus() when qualified discharge begins. The bq2084-V150 sets VDQ
= 0 if any disqualifying condition occurs. FCC cannot be reduced by more than 256 mAh or increased by more
than 512 mAh during any single update cycle. The bq2084-V150 saves the new FCC value to the data flash
within 4 seconds of being updated.
End-of-Discharge Thresholds and Capacity Correction
The bq2084-V150 monitors the battery for three low-voltage thresholds, EDV0, EDV1, and EDV2. The EDV
thresholds can be programmed for determination based on the overall pack voltage or an individual cell level.
The EDVV bit in Pack Configuration DF 0x28 configures the bq2084-V150 for overall voltage or single-cell EDV
thresholds. If programmed for single-cell EDV determination, the bq2084-V150 determines EDV on the basis of
the lowest single-cell voltage. Fixed EDV thresholds must be programmed in EMF/EDV0 DF 0x95-0x96, EDV C0
Factor/EDV1 DF 0x97-0x98, and EDV R Factor/EDV2 DF 0x99-0x9a.
If the CEDV bit in Gauge Configuration DF 0x29 is set, automatic compensated EDVs are enabled and the
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