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BQ34Z100-G1: Implementation with 2 wires pack

Benoit FARINOTTE
Prodigy 90 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100, GPCCHEM, GPCRB

Hi All,

I'am currently implementing a BQ34Z100 with a 1S8P LiFePo4 two wire protected pack.

I choose a listed chem ID (expected to be close, same manufacturer and chemistry) and I ran a successful learning cycle, however I got a quite poor precision, and I suspect the pack setup to be the root cause. If a run GPC chem ID matching tool, I get a high deviation warning.

BQ34Z100 is used on application board, and assembled pack shows a quite high total impedance (Cells assembly + PCM resistance + wire + connector = approx 150 mOhms). BQ34Z100 Batt pin is referenced on pack output + (right after batt connector), and not on raw cell + as suggested by most designs . So I guess the voltage bounces due to load change as seen by the gauge are far higher than expected if measures was taken directly on the cells. I guess than this explain my GPC mismatch

Attached a charge/discharge log and pack setup used for GPC.

Curve screenshot :

So here are my question : 

- How can I teach the BQ34Z100 to work with this profile. Which Chem ID to be used for such case ?

And two additionnal questions about gauge status for assembled product :

- What if the impact of having a application load cycle preventing the status to update (on real-case application, we never have the needed rest time to allow OCV flag to be raised, especially with our LIfePo4 which are requiring an endless rest time to be fully relaxed), so most probably, the status will remains at 4, and perhaps 5 in some cases, but almost never reach 6.

- What it the impact of shipping a product with IT disabled (status 2 instead of 4). It is only preventing the gauge to update along the battery life (so "just" a  lack of precision), or is it also preventing a normal operation and lead to false data.

Thanks,

Benoît

4555.Logsfiles.zip

  • 0
    TI__Genius 10830 points
    Bonjour Benoît,
    One of our BMS experts has been assigned to your issue and will answer shortly.

    Regards,
    David
  • 0 in reply to David Hien
    Prodigy 90 points
    Hi David,

    I still did'nt received any update about this issue. Could you please provide me a status ? If any additionnal detail is needed, i will be happy to provide it.

    Thanks !

    Best regards

    Benoît
  • 0 in reply to Benoit FARINOTTE
    TI__Mastermind 25955 points
    Hi Benoit,

    Thank you for the files. To improve the results for a chemID match, please remove a cell from the pack and reduce to the discharge rate to C/10. Please ensure that the DOD drop is greater than 90% by fully charging the cell and discharging to the terminate voltage of 2.5 V as listed in the cell datasheet.

    Update Status of 06 should be achieved before shipping the product. The golden image that will ultimately be utilized in production is created after achieving a status update of 0x06. In creating the golden image, you will modify the update status from 0x06 to 0x02 indicating that the qmax and ra data are learned, but IT is not yet enabled. After programming the device with the golden file as one of the last steps for production, enable IT and seal the device. Sending the command to enable IT will change the update status from 0x02 to 0x06 because the pack was already learned when creating the golden image.

    Please enable IT before shipping the product. Without IT Enabled, the device will not update the RA tables essential for gauging. Moreover, without running a successful learning cycle, the impedance curves of the ChemID will not update to fit your 8P configuration, thereby causing the gauge to report incorrectly.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 90 points
    Hi Brian,

    Thanks for your answer. But i'am still confuse for few points :
    - When you said "remove a cell from the pack" for matching, I guess you mean I should run the matching on a single cell, not on a 7cell pack, correct ?
    - Could you please confirm I can do the Chem ID matching and GPC low temp optimization using one cell only, and then carry a learning cycle with full assembled pack ? Without compromising the accuracy.
    - Could you please confirm my pack overall impedance (including PCM / wires / connector) is not too high, and will not cause mismatch between the chem ID intented impedance curve, and the impedance measured on pack output (as I will monotor battery voltage only on the pack output, not at a cell level (Taking the datasheet wording, I can only access Pack+, not Batt+).

    Concerning IT command, that's crystal clear, thanks.

    Best regards

    Benoît
  • 0 in reply to Benoit FARINOTTE
    TI__Genius 14985 points
    You can use either a single separated cell (ideal) or the entire pack but will need to use the correct options in the configuration file before submitting to GPC to tell the tool whether it is a single cell or multiple cells.
    For step one (GPCCHEM) you can use either a single cell or the entire pack.
    For step two (GPCRA) it makes sense to use the pack if your gauge is connecting to the pack terminals externally and not located inside the pack. This will enable it to calculate resistance as seen by the gauge. Then you can skip the learning cycle.
    For step three (GPCRB) the same reasoning applies as step two so use the pack.