SLUAAA1 October   2021 BQ21061 , BQ21062 , BQ24179 , BQ25150 , BQ25155 , BQ25157 , BQ25672 , BQ25790 , BQ25792 , BQ25798 , BQ25882 , BQ25883 , BQ25887 , BQ25895 , BQ25896 , BQ25898 , BQ25898D

 

  1.   Trademarks
  2. 1Introduction
  3. 2Battery Characterization
  4. 3Generating the Lookup Table
  5. 4BQ25155 Register Configuration
  6. 5Best Use Cases
  7. 6Python Lookup Table Generator
  8. 7MSP430 Code Snippet

5 Best Use Cases

There are some limitations to the method discussed that must be noted. SOC is known to be a function of the cells open-circuit voltage (OCV). This method assumes that SOC is a function of the cells terminal voltage. This approximation is most accurate under the following conditions:

  1. When the systems load profile resembles a constant current discharge (like what was used to characterize the battery). Having varying currents introduces some error that can be tolerable based on application and magnitude of current variance.
  2. Low cycle-count batteries. High cycle-count batteries undergo changes in their resistance causing a different loaded voltage profile.
  3. Low currents (< C/10). Batteries that are discharged at low C rates experience less voltage relaxation. If a low C rate discharge of a battery is halted (system going to sleep mode), the amount of SOC error introduced due to the upward relaxation is less than a battery discharging at a high rate.
  4. Room temperature. At the extremes, hot and cold temperatures can shift a cell's OCV considerably. Expect increased error as the cell temperatures deviates from the temperature it was characterized at.

A voltage-based fuel gauge to consider is the BQ27621-G1. This gauge achieves higher accuracy by estimating the current based on the terminal voltage. This gauge is appropriate for low current applications where a true coulomb-counting gauge can have issues with current measurement accuracy. One such coulomb counting gauge to consider is the BQ27421-G1.