• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 476 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

bq78pl114S12 VLAN failure

Heye Heegardt
Prodigy 140 points
Other Parts Discussed in Thread: BQ76PL102, BQ78PL114

We are currently developing an 11S1P battery pack using the bq78pl114S12 and 4 of the bq76pl102. Working already on revision 3 of our design we suddenly face the occasional occurence of a VLAN failure. Has anybody encountered a similar problem before ? I would love to hear about workarounds or causes for such a failure since we are basically at our wits end. Documentation about the PowerLAN bus is rather non-existent, so perhaps there is a TI engineer who can help out in our special case without telling too much ? Kind regards, Heye

  • 0
    TI__Intellectual 1940 points

    It could be that the application of cell voltages to the board is not in the proper order.  Please see the attached document with an in depth explanation of how the cell voltages are used in the bq78PL114/6 and the bq76PL102 and the cell connection sequence.  There may already be a post on this site talking about this.  Plus, this information will be going into the datasheets very soon.

    PowerSequence for bq78PL114_6.pdf
  • 0 in reply to Jim M15252
    Prodigy 140 points

    Hello Jim,

    sorry, I didn't know the meaning of the Verify-Button. Thanks for your information anyway, it might prove to be helpful.

    However, I think my question is not answered fully yet, because I need to provide more specific information : Every single VLAN failure we encountered was accompanied by the discharge of only cells 9 and 10. In the beginning it wasn't clear what came first, the discharge, leading to the powerdown of bq76pl102 number 3 and subsequently a VLAN failure or the VLAN failure leading to the discharge of cells 9 and 10.

    Most recently we found a VLAN failure without cell discharge in the beginning. We left the battery pack alone for a couple of days and than discovered the discharge of cells 9 and 10.

    Combined with the knowledge, that the balancing software within the bq76pl102 sometimes stays locked in a loop (caused by a VLAN failure), we developed the following theory:

    1. The current cell situation requires a pump from cell 10 up to cell 11 and at the same time a pump from cell 9 down to cell 8.
    2. Balancing signals P10N and P9S are activated.
    3. The frequencies on P10N and P9S or the balancing currents through the respective inductors cause the PowerLAN bus to fail (due to close routing of the tracks on the pcb).
    4. The balancing software in the bq76pl102 locks and the respective FETs of P10N and P9S stay conducting.
    5. Cells 9 and 10 discharge with a current determined by the dc resistance of the inductor and the 10 Ohms of another series resistor.

    Is this a probable scenario?

    Have you ever encountered a sporadic partial discharge of just the 2 cells of one bq76pl102 ?

    My feeling is, we might have a problem with the design of our battery pack, but debugging is really hard, because we can not really dig into the inside of the PowerLAN controllers. We didn't even manage to reproduce the error. Can you give us a few hints ?

    Cheers, Heye

     

     

     

  • 0 in reply to Heye Heegardt
    Prodigy 140 points

    Hi,

    here's another question: Chapter 2.18 of the Technical Reference for the bq78pl114 describes the activation criteria for a PowerLAN failure. But how ist the VLAN failure flag reset?

    Is the VLAN flag a sticky flag or is it reset straight after removal of the error condition ?

    Regards,

    Heye