SLUA450A January   2008  – November 2022 BQ27421-G1 , BQ27425-G2A , BQ27425-G2B , BQ27441-G1 , BQ27505-J2 , BQ27505-J3 , BQ27505-J4 , BQ27505-J5 , BQ27520-G4 , BQ27530-G1 , BQ27531-G1 , BQ27545-G1 , BQ27546-G1 , BQ27741-G1 , BQ40Z50 , BQ40Z50-R1 , BQ40Z50-R2

 

  1.   Theory and Implementation of Impedance Track™ Battery Fuel-Gauging Algorithm in bq2750x Family
  2.   Trademarks
  3. 1Summary of the Algorithm Operation
  4. 2Parameters Updated by the Gas Gauge in More Detail
    1. 2.1 Modes of Algorithm Operation
    2. 2.2 Update of Chemical Depth of Discharge (DOD)
    3. 2.3 Update of Qmax
    4. 2.4 Update of Resistance
    5. 2.5 Update of Temperature Model
    6. 2.6 Update of DataRAM.Remaining Capacity (RM) and DataRAM.Full Charge Capacity (FCC)
    7. 2.7 Update of DataRAM.Remaining Capacity( ) and DataRAM.State Of Charge( ) Values
  5. 3Real Application Example
    1. 3.1 GSM Smart Phone Application
  6. 4Revision History

1 Summary of the Algorithm Operation

The gas gauge algorithm uses three types of information to calculate remaining capacity (DataRAM.Remaining Capacity( )) and full-charge capacity (DataRAM.Full Charge Capacity( )).

  1. Chemical: depth of discharge (DOD) and total chemical capacity Qmax
  2. Electrical: internal battery resistance dependence on DOD
  3. External: load and temperature

DataRAM.Full Charge Capacity( ) is defined as the amount of charge passed from a fully charged state until the voltage defined in DF.Terminate Voltage flash constant is reached at a given rate of discharge, after subtracting the reserve capacity (DF.Reserve Capacity).

Note that DataRAM.Full Charge Capacity( ) depends on the rate of discharge and is lower at higher rates and low temperatures because the cell I*R drop causes the Terminate Voltage threshold to be reached earlier.