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SLUS732 – SEPTEMBER 2006
bq2084-V143 computes the EDV0, EDV1, and EDV2 voltage thresholds based on the values in DF 0x95-0xa0
and the battery's current discharge rate and temperature. If FEDV0 in
Gauge Configuration
is also set then
EDV0 is not compensated. The bq2084-V143 disables EDV detection if Current( ) exceeds the
Overload Current
threshold programmed in DF 0x5b-DF 0x5c. The bq2084-V143 resumes EDV threshold detection after Current( )
drops below the
Overload Current
threshold. Any EDV threshold detected is reset after charge is detected and
VDQ is cleared after 10 mAh of charge.
The bq2084-V143 uses the EDV thresholds to apply voltage-based corrections to the RM register according to
Table 2. State-of-Charge Based on Low Battery Voltage
THRESHOLD
EDV0
EDV1
EDV2
RELATIVE STATE OF CHARGE
0%
3%
Battery Low %
The bq2084-V143 performs EDV-based RM adjustments with
Current()≤
C/32. No EDV flags are set if current <
C/32.
The bq2084-V143 adjusts RM as it detects each threshold. If the voltage threshold is reached before the
corresponding capacity on discharge, the bq2084-V143 reduces RM to the appropriate amount as shown in
If an RM % level is reached on discharge before the voltage reaches the corresponding threshold, then RM is
held at that % level until the threshold is reached. RM is only held if VDQ = 1, indicating a valid learning cycle is
in progress. If
Battery Low
% is set to zero, EDV1 and EDV0 corrections are disabled.
EDV Thresholds and Near-Full Programming
The bq2084-V143 uses the values stored in data flash for the EDV0, EDV1, and EDV2 values or calculates the
three thresholds from a base value and the temperature, capacity, and rate adjustment factors stored in data
flash. If EDV compensation is disabled, then EDV0, EDV1, and EDV2 are stored directly in mV in DF 0x95-0x96,
DF 0x97-0x98, and DF 0x99-0x9a, respectively.
For capacity correction at EDV2,
Battery Low %
DF 0x2f can be set at a desired state-of-charge,
STATEOFCHARGE%,
in the range of 3-19%. Typical values for
STATEOFCHARGE%
are 5-7%, representing
5-7% capacity.
Battery Low %
= (STATEOFCHARGE% x 2.56)
The bq2084-V143 updates FCC if a qualified discharge occurs from a near-full threshold of FCC -
Near Full,
until EDV2 condition is reached. The desired near-full threshold window is programmed in
Near Full
in DF 0x30,
0x31 in mAh.
EDV Discharge Rate and Temperature Compensation Programming
If EDV compensation is enabled, the bq2084-V143 calculates battery voltage to determine EDV0, EDV1, and
EDV2 thresholds as a function of battery capacity, temperature, and discharge load. The general equation for
EDV0, EDV1, and EDV2 calculation is
EDV0,1,2 = n (EMF
×
FBL – | ILOAD |
×
R0
×
FTZ)
EMF is a no-load cell voltage higher than the highest cell EDV threshold computed. EMF is programmed
in mV in
EMF/EDV1
DF 0x95-0x96.
ILOAD is the current discharge load magnitude.
n = the number of series cells
FBL is the factor that adjusts the EDV voltage for battery capacity and temperature to match the no-load
characteristics of the battery.
FBL = f ( C0, C + C1, T )
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