BQ2085 Datasheet, PDF (11/56 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

bq2085
SLUS541 – OCTOBER 2002
The bq2085 sets VDQ=1 in pack status when qualified discharge begins. The bq2085 sets VDQ=0 if any
disqualifying condition occurs. FCC cannot be reduced by more than 256 mAh or increased by more than
512 mAh during any single update cycle. The bq2085 saves the new FCC value to the data flash within 4
seconds of being updated.
End-of-Discharge Thresholds and Capacity Correction
The bq2085 monitors the battery for three low-voltage thresholds, EDV0, EDV1, and EDV2. The EDV
thresholds can be programmed for determination based on the overall pack voltage or an individual cell level.
The EDVV bit in Pack Configuration DF 0x28 configures the bq2085 for overall voltage or single-cell EDV
thresholds. If programmed for single cell EDV determination, the bq2085 determines EDV on the basis of the
lowest single-cell voltage. Fixed EDV thresholds may be programmed in EMF/EDV0 DF 0x84-0x85, EDV C0
Factor/EDV1 DF 0x86-0x87, and EDV R Factor/EDV2 DF 0x88-0x89. If the CEDV bit in Gauge Configuration
DF 0x29 is set, automatic EDV compensation is enabled and the bq2085 computes the EDV0, EDV1, and EDV2
thresholds based on the values in DF 0x84-0x8d and the battery’s current discharge rate and temperature. The
bq2085 disables EDV detection if Current( ) exceeds the Overload Current threshold programmed in DF 0x58
– DF 0x59. The bq2085 resumes EDV threshold detection after Current( ) drops below the Overload Current
threshold. Any EDV threshold detected is reset after charge is applied and VDQ is cleared after 10mAh of
charge.
Table 2. State of Charge Based on Low Battery Voltage
THRESHOLD
EDV0
EDV1
EDV2
RELATIVE STATE OF CHARGE
0%
3%
Battery Low %
The bq2085 uses the EDV thresholds to apply voltage-based corrections to the RM register according to
Table 1. The bq2085 performs EDV-based RM adjustments with Current( ) ≥ C/32. No EDVs are set if current
< C/32. The bq2085 adjusts RM as it detects each threshold. If the voltage threshold is reached before the
corresponding capacity on discharge, the bq2085 reduces RM to the appropriate amount as shown in Table 2.
This reduction occurs only if current ≥ C/32 when the EDV threshold is detected. If RM reaches the capacity
level before the voltage threshold is reached on discharge, the bq2085 prevents RM from decreasing further
until the battery voltage reaches the corresponding threshold only on a full learning cycle discharge. RM is not
held at the associated EDV percentage on a nonlearning discharge cycle (VDQ=0) or if current < C/32.
If Battery Low % is set to zero, EDV1 and EDV0 corrections are disabled.
Table 3. bq2085 Register Functions
FUNCTION
ManufacturerAccess
RemainingCapacityAlarm
RemainingTimeAlarm
BatteryMode
AtRate
AtRateTimeToFull
AtRateTimeToEmpty
AtRateOK
Temperature
Voltage
Current
AverageCurrent
MaxError
COMMAND CODE
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0a
0x0b
0x0c
ACCESS
read/write
read/write
read/write
read/write
read/write
read
read
read
read
read
read
read
read
UNITS
NA
mAh, 10 mWh
minutes
NA
mA, 10mW
minutes
minutes
Boolean
0.1°K
mV
mA
mA
percent
www.ti.com
11