BQ2014_15 Datasheet, PDF (5/27 Pages) Texas Instruments – Gas Gauge IC with External Charge Control

Not Recommended For New Designs
bq2014
Gas Gauge Operation
The operational overview diagram in Figure 2 illustrates
the operation of the bq2014. The bq2014 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
bq2014 adapts its capacity determination based on the
actual conditions of discharge.
The battery's initial capacity is equal to the Pro-
grammed 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 al-
lows the gas gauge to be charger-independent and com-
patible with any type of charge regime.
Many actions in the bq2014 are triggered by detection of
a “valid charge.” NAC is stored in an asynchronous, 2-
byte counter; the lower byte is NACL and the upper byte
is NACH. A valid charge has occurred anytime the
charge lasts long enough to cause an increment in
NACH. Small increments of charging are not consid-
ered “valid” if they result in counts in NACL but do not
generate a roll-over (carry) that increments NACH.
NACL is reset anytime the counter direction changes
from down to up, so the number of counts required to
cause a roll-over and a valid charge is always 256. The
counter may be incrementing by 2, 4, 8, or more counts
per increment, however, depending on the scaling fac-
tors selected. Therefore, a valid charge may be consti-
tuted by a smaller number of counter increments.
1. Last Measured Discharge (LMD) or
learned battery capacity:
LMD is the last measured discharge capacity of the
battery. On initialization (application of VCC 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
battery capacity:
The initial LMD and gas gauge rate values are pro-
grammed by using PROG1—PROG4. The bq2014 is
configured for a given application by selecting a
PFC value from Table 2. The correct PFC may be
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