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Original question:

BQ27426: Learning cycle when device is in the market

BQ27426: Correct cycle for updating Qmax and Ra tables

Oscar Aurin
Intellectual 290 points
Part Number: BQ27426
Other Parts Discussed in Thread: BQSTUDIO, GPCCHEM

From what I've understood from previous questions, Qmax and the Ra table should continuously be stored by the host and written to the gauge on POR. Our device has host and gauge permanently connected to the battery. A PCM will cut power at 3V and the user can place the device in a charger, which will power the board and charge the battery. Some questions regarding to the cycle(s) of this:

  • Are Qmax and the Ra table updated only once before reset occurs? If not, when are the QMAX_UP and RES_UP flags cleared? (Note that the gauge is permanently connected to the battery)
  • When performing a learning cycle, the battery needs to be discharged. This means that the gauge will loose power (since the PCM will cut the power). How does this work with this ROM-based device?
  • How important is it to generate the golden image, if Qmax and the Ra table is continuously updated, and the chemistry is a good match?

In essence: will the behaviour be correct if we store Qmax and the Ra table once the flag(s) are set and then write these values on startup (i.e. when ITPOR is set)?

  • 0
    TI__Guru* 76230 points
    Hi Oscar,

    -qmax and resistance are continuously updated during device use. resistance is updated during discharge, qmax is updated 37% passed charge has occured and the device has taken to OCV measurements before and after the discharge or charge.
    -No if you do not discharge the battery below the shutdown voltage , the gauge will still stay powered on. The gauge needs to stay powered on for learning to complete.
    -the golden file with the updated qmax and resistance tables are important for the accurracy of the other units.if you will perform cycles on each pack so they learn their individual qmax and resistance table values then you are ok,

    During use, the gauge will continuously update qmax and resistance to ensure accuracy is maintained.

    tahnks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 290 points
    Thank you, Onyx.

    So once set the flags are not cleared unless a reset occurs?
    Is it then correct to store the values when placed in and when removed from the charger?
  • 0 in reply to Oscar Aurin
    TI__Guru* 76230 points
    it depends on what flags you are talking about. The qmax and ra paramaters will not get reset except power is cut off from the gauge. monitor the ITPOR flags to determine when to reprogram the values stored in the NVM
  • 0 in reply to Onyx Ahiakwo
    Intellectual 290 points

    I was referring to the QMAX_UP and RES_UP flags. I'm asking, because, if I have understood this correctly, Qmax and the Ra table can be updated multiple times as long as the gauge is powered. QMAX_UP and RES_UP can then be polled until set and Qmax and the Ra table can then be stored to host's NVM.

    But polling the flags can only be done the first time - consecutive updates must be acquired when place in / remove from charger (or other suitable interval)?

  • 0 in reply to Oscar Aurin
    TI__Guru* 76230 points
    Hi Oscar
    placing or removal from the charger does not cause qmax and res_up flags to get set. Like you mentioned Those flags can be polled to determine when to update qmax and ra table values in your host nvm.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 290 points

    Hi Onyx,

    Thanks, I understand. So the flags are cleared when polled? (If I poll the control register every second (definitely not saying its recommended) and store the Ra table and Qmax when the flags are set, I won't end up saving the parameters every second?)

  • 0 in reply to Oscar Aurin
    TI__Mastermind 42535 points
    No, the flags are not cleared when polled, Oscar. You have the choice of storing data per when they are set. However, once set even after a second Ra or Qmax update they are not reset. You can only use the flags once.
  • 0 in reply to Batt
    Intellectual 290 points

    Hi Batt,

    Thanks for the clarification. So a possible strategy is then to read Qmax and the Ra table when placed in the charger, as that is the most likely time they would have been updated? (SLUUBN3) Or, use BqStudio to acquire a golden image and only write the Ra table and Qmax once (on ITPOR)?

    What accuracy can I expect for the following scenarios:

    • Create a golden image for Qmax and Ra table and never modify them after production?
    • Continuously updating Qmax and the Ra table (according to SLUUBN3)?
    • Ignoring Qmax and the Ra table and leaving them to default?

  • 0 in reply to Oscar Aurin
    TI__Guru* 76230 points
    Create a golden image for Qmax and Ra table and never modify them after production?
    Initially good accuracy but as the cells age accuracy will get worse. The purpose of the updates is to account for aging
    Continuously updating Qmax and the Ra table (according to SLUUBN3)?
    You will get great accuracy
    Ignoring Qmax and the Ra table and leaving them to default?
    terrible accuracy. Can be as bad as 50% or worse depending on how closely matched your cells are to the default table. pls use our online tool gpcchem to determine how close your battery matches the default chem ids.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 290 points
    Excellent! Thank you very much for the support!
  • 0 in reply to Onyx Ahiakwo
    Intellectual 290 points
    One more question; figure 2 in SLUUBN3 issues DataClass() and DataBlock() commands before reading the checksum again (to verify that RAM has been updated). Whereas 4.1 in SLUUBB0 omits this.
    Is it necessary to issue the commands?
  • 0 in reply to Oscar Aurin
    TI__Guru* 76230 points
    Hi Oscar

    pls follow the quick start guide. SLUUBN3

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 290 points
    I'll through in another minor question as well. There is a control command for reading the firmware version (FW_VERSION). Does this mean that there is a software loaded onto the device during production, or is the IC pure hardware? I'm asking because we need to make the distinction between software and hardware for regulatory purposes.
  • 0 in reply to Oscar Aurin
    TI__Guru* 76230 points
    What you load during production is the flash stream file. It just contains the configuration settings, which is lost if the gauge undergoes a POR.
    The firmware itself is hard coded on the device.
    thanks
    Onyx