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Safe Disconnect - bq78PL116EVM

Bob White
Intellectual 660 points
Other Parts Discussed in Thread: BQ78PL116, BQ77908A

For unstated reasons, it is considered dangerous to disconnect the battery from the bq78PL116EVM.  To do so, one must press Shift-F2 (Safe Disconnect command) which invokes a popup that times out in 20 seconds.  I'm finding it hard to disconnect all those wires from the EVM in said 20 seconds, especially due to having bare wires floating around that are connected directly to LiPo cells.  Do I have to disconnect the wires in the opposite order of the required connect sequence?  What am I missing here?

Bob

 

  • 0
    TI__Guru 73830 points

    Bob, 

    Safe Disconnect disables portions of the device to prepare it for cell removal. It will disable flash memory writes and prevent cell balancing. Safe Disconnect disables these features for about 20 seconds, then the device returns to normal operation if the cells have not been removed. If you cannot disconnect the cells within 20 seconds, then you can set the wired bit to 0 and this will protect the flash memory. You will have to set the wired bit back to 1 after reconnecting the cells.

    Cells do need to be disconnected in the reverse order to prevent damage to the device.

    Regards
    Tom

  • 0 in reply to ThomasCosby
    Intellectual 660 points

    This raises my next concern.  Production.  How do I go about putting this chip (bq78PL116) in a battery?  Are we expected to solder wires to each cell during assembly?  Do we need a connector that has stepped pins for sequencing (never seen such a thing)?  Are we supposed to build electronic switches to sequence the connections?  Has the '116 actually been used in production?

    Bob

     

  • 0 in reply to Bob White
    TI__Guru 73830 points

    Bob,

    The cell attachment restriction is due to the hardware implementation on the PL114 and PL116 devices. Internal diodes can become forward biased and get damaged.Yes, these devices are in production in several applications and customers do use some of the options that you mentioned to attach the cells.

    We do not have this restriction on other devices, unless it it noted in the published material for that device.

    Newer devices do not have cell attachment sequencing limitations.

    Regards

    Tom

  • 0 in reply to ThomasCosby
    Intellectual 660 points

    Hi Tom,

    You said:

    "Newer devices do not have cell attachment sequencing limitations."

    Are there newer devices to replace the bq78PL116?

    Bob

     

  • 0 in reply to Bob White
    TI__Guru 73830 points

    Bob,

    The bq77908A is a popular protector to use an an alternative solution to the PL116. It cell monitoring and protection for up to 8 series cells. We will release a new gas gauge device very soon that can support the extended pack voltages as well.I can update you after it is released.

    We have other cell management devices that do not have specific cell attachment sequencing requirements available as well.

    Regards

    Tom

  • 0 in reply to ThomasCosby
    Intellectual 660 points

    Hi Tom,

    Please let me know as soon as the new gas gauge protector is available.  I have about 6 months for this project, and  maybe I can work on the uP and software till then.  On the other hand, the '116 is amazing and I'm getting quite involved (I can't say comfortable yet) with it's Wizard.  I'd go with the 908A if it had a gas gauge, even without the PowerPump balancer.  My work so far has been towards understanding the '116 device and trying to determine if the PowerPump is worth the space and weight (every gram counts in my application).  The 212 Chem ID is working so well that I'm wondering if I can do without the .aux file.

    I really appreciate all your support.

    Bob