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bq20z gas gauge accuracy

Ed Walker
Prodigy 5 points
Other Parts Discussed in Thread: BQ20Z90

I would like to have a statement from the factory on the accuracy of impedance track gauging.
ALEXANDER TECH is complaining about getting 3% accuracy.
BQ20Z90
They are using RTE to predict 20 minutes time left, and 5 minutes RTE to force shutdown.
Seeing RTE quickly go to 0 before the 20 minutes, which is about 3% left of capacity

1. I know 1% is a "target"
2. in typical applications what is really achievable
3. what margin do users, like laptops, use for predicting run time
4. is RTE run time to empty used much in real applications
5. what is the best way to design in margin, assure "at least" xxx minutes of time left
6. is there a better part than the Z90 to get higher accuracy?

  • 0
    TI__Expert 6470 points

    1. 1% is usually achievable over the entire range, but depends on many factors including near perfect calibration of the gauge.

    2. Depends on calibration, chemistry match, temperature range of operation, etc.

    3. Not sure, but they probably provide lots of marging since the critical RAM data must be backed up to disk before the battery fails.

    4. Sorry, no data on this.

    5. The Reserve Capacity feature should be used if extra margin is desired.

    6. In general, newer devices are a bit better. As of this writing, the bq20z60 is the best general upgrade for bq20z90.