bq2011K
the NAC register and increment the DCR (Discharge
Count Register).
2. Programmed Full Count (PFC) or initial bat-
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
bq2011K adapts its capacity determination based on the
actual conditions of discharge.
The initial LMD and gas gauge rate values are pro-
grammed by using PFC. The PFC also provides the
100% reference for the absolute display mode. The
bq2011K is configured for a given application by se-
lecting a PFC value from Table 1. The correct PFC
may be determined by multiplying the rated bat-
tery capacity in mAh by the sense resistor value:
The battery’s initial capacity is equal to the Pro-
grammed Full Count (PFC) shown in Table 1. 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.
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.
1. Last Measured Discharge (LMD) or learned
battery capacity:
Example: Selecting a PFC Value
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
EDV. 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.
Given:
Sense resistor = 0.002Ω
Number of cells = 6
Capacity = 1800mAh, NiCd cells
Current range = 1A to 80A
Absolute display mode
C
Self-discharge =
80
Voltage drop across sense resistor = 2mV to 160mV
Charge
Inputs
Discharge
Current
Self-Discharge
Timer
Current
Rate and
Temperature
Compensation
Temperature
Compensation
+
+
-
-
Nominal
Available
Charge
(NAC)
Last
Measured
Discharged Qualified Register
(LMD) (DCR)
Transfer
Discharge
Count
+
<
Main Counters
and Capacity
Reference (LMD)
Temperature Step,
Other Data
Temperature
Translation
Chip-Controlled
Available Charge
LED Display
Serial
Port
Outputs
FG201104.eps
Figure 2. Operational Overview
5
TI [ TEXAS INSTRUMENTS ]
