BQ2085 Datasheet, PDF (9/56 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

bq2085
SLUS541 – OCTOBER 2002
General
The operational overview in Figure 3 illustrates the gas gauge operation of the bq2085. Table 3 describes the
bq2085 registers.
Inputs
Charge
Current
Battery Electronics
Load Estimate
Discharge
Current
Self-Discharge
Timer
Charge
Efficiency
Compensation
Temperature
Compensation
Main Counters and
Capacity Reference (FCC)
–––
Remaining
+ _{Capacity ≤}
(RM)
Full
Charge
Capacity
(FCC)
+++
Qualified
Transfer
Discharge
Count
Register
(DCR)
Temperature, Other Data
Outputs
Chip-Controlled Two-Wire
Available Charge Serial Port
LED Display
Figure 3. bq2085 Operational Overview
The bq2085 accumulates a measure of charge and discharge currents and estimates self-discharge of the
battery. The bq2085 compensates the charge current measurement for temperature and state-of-charge of the
battery. The bq2085 also adjusts the self-discharge estimation based on temperature.
The main charge counter RemainingCapacity( ) (RM) represents the available capacity or energy in the battery
at any given time. The bq2085 adjusts RM for charge, self-discharge, and other compensation factors. The
information in the RM register is accessible through the SMBus interface and is also represented through the
LED display.
The FullChargeCapacity( ) (FCC) register represents the last measured full discharge of the battery. It is used
as the battery full-charge reference for relative capacity indication. The bq2085 updates FCC after the battery
undergoes a qualified discharge from nearly full to a low battery level. FCC is accessible through the SMBus
interface.
The Discharge Count Register (DCR) is a non-accessible register that tracks discharge of the battery. The
bq2085 uses the DCR register to update the FCC register if the battery undergoes a qualified discharge from
nearly full to a low battery level. In this way, the bq2085 learns the true discharge capacity of the battery under
system use conditions.
Main Gas-Gauge Registers
The gas-gauge register functions are described in Table 3.
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