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BQ28Z610: Gauge Settings

Fred Arnold
Intellectual 680 points
Part Number: BQ28Z610

Hi,

I have a few question regarding the best settings that provides the highest accuracy for my application and how to get this into serial production.

It is a non-removable battery for a UPS-like device and it is used in the following way:

- Most of the time it is in shut-down node if not in use.
- If it is in use it is mostly in charge or maintenance charge mode.
- Only in an emergency is the battery discharged. It is discharged at a power rate up-to 10-times the cell capacity but discharge does usually stop before the cells are fully discharged. The entire discharge cycle would take less than 10 minutes to empty. The CUV would in this case stop any further discharge by opening the FET.
- The battery is then either recharged straight away and/or put in shut-down mode for storage until next use.

This workflow does not give the gauge time to do measurements and update settings. some of them might even be lost during the extended shut-down period between deployments.

1. What would be the best gauging configuration to get the highest accuracy out of it?

The second question is how to "initialize" the Gauge on a new production unit after it has been programmed with the golden image. I have noticed that fully charge capacity and relative state of charge is only correct after perform a full discharge - wait 5h -  charge - wait 2h - cycle, which is not practicabe for serial production. Also, the Cell-Balancing is not enabled until update status reaches 0x0E, which will most likely never happen during the normal usage as it is described above.

2. How should I configure the gauge so that it is ready for use after programming the golden image so it shows correct initial state of charge and has cell balancing already enabled?

Thanks for the help,

Fred

  • 0
    TI__Mastermind 42535 points

    Before you get into serial production, you will need to do a learning cycle. Please refer to this document to see what needs to be done. www.ti.com/.../slua777.pdf . Secondly once your cycle is done, if your cell is not LFP, I would suggest disabling smoothing and setting load select to user rate and set the rate to 10C, which is your rate of dsg. These 2 settings would give you better estimation of capacity. Do run a test cycle and see if these settings work. If you still have issues, please contact us.

  • 0 in reply to Batt
    Intellectual 680 points
    Hi Batt,

    The learning cycle has been completed a while ago and that is all fine.
    I also played with the discharge rate set fixed to 10C and constant power mode but gives completely wrong estimates if the rate is lower.
    Anything you could recommend to make it more precise?

    I still have the question with the golden image. I need to run one discharge charge cycle before the state of charge shows the right value and the gauge is calibrated. I cannot invest this time during production. Also the cell balancing, the instruction say I have to set the learning status from 0x0E back to 0x06 before programming the image, which means balancing is disabled until I run a complete discharge/charge cycle on each new unit to bring it back to 0x0E. I need a solution here as well.

    Thanks,
    Fred
  • 0 in reply to Fred Arnold
    TI__Mastermind 42535 points
    You can try setting the load select to 1. It will be aggressive at high currents but that can solve your rate issue.
    You can also set update status back to 0x0A. That way, in production you just need to send IT enable and your update status will turn to 0x0E enabling cell balancing on the gauge.