BQ2012_15 Datasheet, PDF (5/26 Pages) Texas Instruments – Gas Gauge IC With Slow-Charge Control

Not Recommended For New Designs
bq2012
Gas Gauge Operation
1. Last Measured Discharge (LMD) or learned
battery capacity:
The operational overview diagram in Figure 2 illustrates
LMD is the last measured discharge capacity of the
the operation of the bq2012. The bq2012 accumulates a
measure of charge and discharge currents, as well as an
battery. On initialization (application of V_CC or bat-
tery replacement), LMD = PFC. During subsequent
estimation of self-discharge. Charge and discharge cur-
discharges, the LMD is updated with the latest
rents are temperature and rate compensated, whereas
measured capacity in the Discharge Count Register
self-discharge is only temperature compensated.
(DCR) representing a discharge from full to below
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
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.
the NAC register and increment the DCR (Discharge _{2. Programmed Full Count (PFC) or initial bat-}
Count Register).
tery capacity:
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
bq2012 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 up-
dated, 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.
The initial LMD and gas gauge rate values are pro-
grammed by using PROG₁–PROG₄. The PFC also
provides the 100% reference for the absolute dis-
play mode. The bq2012 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.
Inputs
Charge
Current
Rate and
Temperature
Compensation
Discharge
Current
Rate and
Temperature
Compensation
Self-Discharge
Timer
Temperature
Compensation
Main Counters
and Capacity
Reference (LMD)
--
++
< ⁺
Nominal
Available
Last
Measured
Discharge
Count
Charge
Discharged Qualified Register
(NAC)
(LMD) Transfer (DCR)
Temperature
Translation
Temperature Step,
Other Data
Outputs
Chip-Controlled
Available Charge
LED Display
Serial
Port
FG201002.eps
Figure 2. Operational Overview
5