BQ2092_15 Datasheet, PDF (8/30 Pages) Texas Instruments – Gas Gauge IC with SMBus-Like Interface

Obsolete Device
bq2092
in full charge percentage, RM is set to full charge
percentage of FCC on valid charge termination. If RM is
above the full charge percentage, RM is not modified.
Count Compensations
Charge activity is compensated for temperature and
state-of-charge before updating the RM and/or DCR. RM
is compensated for temperature before updating the RM
register. Self-discharge estimation is compensated for
temperature before updating RM or DCR.
Charge Compensation
Charge efficiency is compensated for state-of-charge,
temperature, and battery chemistry. For Li-Ion chemis-
try cells, the charge efficiency is unity for all cases. The
charge efficiency for nickel chemistry cells, however, is
adjusted using the following equation:
RM = RM ∗ (Q _EFC − Q _ET )
where RelativeStateofCharge ≤ FullChargePercentage
and Q _EFC is the programmed fast charge efficiency vary-
ing from .75 to .99.
RM = RM ∗ (Q _ETC − Q _ET )
where RelativeStateofCharge ≥ FullChargePercentage
and Q _ETC is the programmed maintenance (trickle)
charge efficiency varying from 0.50 to 0.97.
Q _ET is used to adjust the charge efficiency as the battery
temperature increases according to the following:
Q _ET = 0 if T < 30°C
Q _ET = 0.02 if 30°C ≤ T < 40°C
Q _ET = 0.05 if T ≥ 40°C
Remaining Capacity Compensation
The bq2092 adjusts the RM as a function of tempera-
ture. This adjustment accounts for the reduced capacity
of the battery at colder temperatures. The following
equation is used to adjust RM:
If T ≥ 5°C
RemainingCapacity =
Nominal Available Capacity (NAC)
If T < 5°C
RM() = NAC() (1 + TCC ∗ (T − 5°C))
Where T = temperature °C
TCC = 0.004
Table 2. Typical Digital Filter Settings
DMF
75
100
150 (default)
175
200
DMF
Hex.
4B
64
96
AF
C8
|VSRD (mV)|
±0.60
±0.45
±0.30
±0.26
±0.23
RM adjusts upward to Nominal Available Capacity as
the temperature increases.
Digital Magnitude Filter
The bq2092 has a programmable digital filter to elimi-
nate charge and discharge counting below a set
threshold. Table 2 shows typical digital filter settings.
The proper digital filter setting can be calculated
using the following equation.
|VSRD (mV)| = 45 / DMF
Error Summary
Capacity Inaccurate
The FCC is susceptible to error on initialization or if no
updates occur. On initialization, the FCC value includes
the error between the design capacity and the actual
capacity. This error is present until a valid discharge
occurs and FCC is updated (see the DCR description on
page 6). The other cause of FCC error is battery wear-
out. As the battery ages, the measured capacity must be
adjusted to account for changes in actual battery capac-
ity. Periodic discharges from full to empty will mini-
mize errors in FCC.
Current-Sensing Error
Table 3 illustrates the current-sensing error as a func-
tion of VSR. A digital filter eliminates charge and
discharge counts to the RM register when VSRO is
between VSRQ and VSRD.
Display
The bq2092 can directly display capacity information
using low-power LEDs. The bq2092 displays the battery
charge state in either absolute or relative mode. In rela-
tive mode, the battery charge is represented as a
percentage of the FCC. Each LED segment represents
25% of the FCC.
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