BQ2014H Datasheet, PDF (5/22 Pages) Texas Instruments – Low-Cost NiCd/NiMH Gas Gauge IC

Preliminary bq2014H
Gas Gauge Operation
The operational overview diagram in Figure 2 illustrates
the operation of the bq2014H. The bq2014H accumu-
lates a measure of charge and discharge currents, as
well as an estimation of self-discharge. The accumu-
lated charge and discharge currents are adjusted for
temperature and rate to provide the indication of com-
pensated available capacity to the host system or user.
The main counter, Nominal Available Capacity (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 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 bq2014H adapts
its capacity determination based on the actual condi-
tions of discharge.
The battery's initial capacity equals 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.
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
representing a discharge from full to below EDV1.
A qualified discharge is necessary for a capacity
transfer from the DCR to the LMD register. The
LMD also serves as the 100% reference threshold
used by the relative display mode.
Inputs
Charge
Current
Discharge
Current
Self-Discharge
Timer
Rate and
Temperature
Compensation
Temperature
Compensation
Main Counters
and Capacity
Reference (LMD)
--
++
< ⁺
Nominal
Available
Last
Measured
Discharge
Count
Charge
Discharged Qualified Register
(NAC)
(LMD) Transfer (DCR)
Rate and
Temperature
Compensation
Temperature Step,
Other Data
Outputs
Compensated
Available Charge
LED Display, etc.
Serial
Port
Figure 2. Operational Overview
F2014HOO.eps
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