Datasheet

Gas Gauge Operation
The operational overview diagram in Figure 2 illustrates
the operation of the bq2010. The bq2010 accumulates a
measure of charge and discharge currents, as well as an
estimation of self-discharge. Charge and discharge cur
-
rents are temperature and rate compensated, whereas
self-discharge is only temperature compensated.
The main counter, Nominal Available Charge (NAC),
represents the available battery capacity at any given
time. Battery charging increments the NAC register,
while battery discharging and self-discharge decrement
the NAC register and increment the DCR (Discharge
Count Register).
The Discharge Count Register (DCR) is used to update
the Last Measured Discharge (LMD) register only if a
complete battery discharge from full to empty occurs
without any partial battery charges. Therefore, the
bq2010 adapts its capacity determination based on the
actual conditions of discharge.
The battery's initial capacity is equal to the Programmed
Full Count (PFC) shown in Table 2. Until LMD is updated,
NAC counts up to but not beyond this threshold during
subsequent charges. This approach allows the gas gauge to
be charger-independent and compatible with any type of
charge regime.
1.
Last Measured Discharge (LMD) or learned
battery capacity:
LMD is the last measured discharge capacity of the
battery. On initialization (application of V
CC
or bat
-
tery replacement), LMD = PFC. During subsequent
discharges, the LMD is updated with the latest
measured capacity in the Discharge Count Register
(DCR) representing a discharge from full to below
EDV1. A qualified discharge is necessary for a ca
-
pacity transfer from the DCR to the LMD register.
The LMD also serves as the 100% reference thresh
-
old used by the relative display mode.
2.
Programmed Full Count (PFC) or initial bat
-
tery capacity:
The initial LMD and gas gauge rate values are pro
-
grammed by using PROG
1
–PROG
4
. The PFC also
provides the 100% reference for the absolute dis
-
play mode. The bq2010 is configured for a given ap
-
plication by selecting a PFC value from Table 2.
The correct PFC may be determined by multiplying
the rated battery capacity in mAh by the sense re
-
sistor value:
Battery capacity (mAh)
*
sense resistor (
Ω
) =
PFC (mVh)
Selecting a PFC slightly less than the rated capac-
ity for absolute mode provides capacity above the
full reference for much of the battery's life.
5
bq2010
FG201002.eps
Rate and
Temperature
Compensation
Temperature
Compensation
Charge
Current
Discharge
Current
Self-Discharge
Timer
Temperature
Translation
Nominal
Available
Charge
(NAC)
Last
Measured
Discharged
(LMD)
Discharge
Count
Register
(DCR)
<
Qualified
Transfer
+
Rate and
Temperature
Compensation
Rate and
Temperature
Compensation
Temperature Step,
Other Data
+
--
+
Inputs
Main Counters
and Capacity
Reference (LMD)
Outputs
Serial
Port
Chip-Controlled
Available Charge
LED Display
Figure 2. Operational Overview