BQ2085 Datasheet, PDF (43/56 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

bq2085
PROGRAMMING INFORMATION
SLUS541 – OCTOBER 2002
DATA FLASH PROGRAMMING
The following sections describe the function of each data flash location and how the data is to be stored.
Fundamental Parameters
Sense Resistor Value
The 32-bit CC Delta DF 0xbc–0xbf corrects the coulomb counter for sense resistor variations. It represents the
gain factor for the coulomb counter.
The 16-bit Sense Resistor Gain in DF 0xba-0xbb scales each integrating converter conversion to mAh. The
Current( ) related measurement Sense Resistor Gain is based on the resistance of the series sense resistor.
The following formula computes a nominal or starting value for Sense Resistor Gain from the sense resistor
value.
Sense
Resistor
Gain
+
306.25
Rs
(2)
Digital Filter
The desired digital filter threshold, VDF (V), is set by the value stored in Digital Filter DF 0x2b.
Digital
Filter
+
VDF
290 nV
(3)
Cell and Pack Characteristics
Battery Pack Capacity and Voltage
Pack capacity in mAh units is stored in Design Capacity, DF 0x31–0x32. In mAh mode, the bq2085 copies
Design Capacity to DesignCapacity( ). In mWh mode, the bq2085 multiplies Design Capacity by Design Voltage
DF 0x04–0x05 to calculate DesignCapacity( ) scaled to 10 mWh. Design Voltage is stored in mV.
The initial value for Last Measured Discharge, in mAh, is stored in DF 0x35–0x36. Last Measured Discharge
is modified over the course of pack usage to reflect cell aging under the particular use conditions. The bq2085
updates Last Measured Discharge in mAh after a capacity learning cycle. The bq2085 uses the Last Measured
Discharge value to calculate FullChargeCapacity( ) in units of mAh or 10 mWh.
Remaining Time and Capacity Alarms
Remaining Time Alarm in DF 0x00-0x01 and Remaining Capacity Alarm in 0x02-0x03 set the alarm thresholds
used in the SMBus command codes 0x01 and 0x02, respectively. Remaining Time Alarm is stored in minutes
and Remaining Capacity Alarm in units of mAh or 10 mWh, depending on the BatteryMode( ) setting.
EDV Thresholds and Near Full Percentage
The bq2085 uses three pack-voltage thresholds to provide voltage-based warnings of low battery capacity. The
bq2085 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 0x84–0x85, DF
0x86–0x87, and DF 0x88–0x89, respectively.
For capacity correction at EDV2, Battery Low % DF 0x2e 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% • 2.56)
(4)
The bq2085 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 0x2f, 0x30
in mAh.
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