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SLUS732 – SEPTEMBER 2006
Figure 1. bq2084-V143 Gas Gauging Operational Overview
The bq2084-V143 accumulates a measure of charge and discharge currents and estimates self-discharge of the
battery. The bq2084-V143 compensates the charge current measurement for temperature and state-of-charge of
the battery. The bq2084-V143 also adjusts the self-discharge estimation based on temperature.
The main charge counter
RemainingCapacity()
(RM) represents the available capacity or energy in the battery at
any given time. The bq2084-V143 adjusts RM for charge, self-discharge, and other compensation factors. The
information in the RM register is accessible through the SMBus interface and is also represented through the
LED display.
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-V143 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-V143 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-V143 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-V143 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-V143
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.
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