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BQ76930: Behavior in shipping mode and changed cell configuration

Marcel Bullen
Prodigy 30 points
Part Number: BQ76930
Other Parts Discussed in Thread: BQ76920
I would like to use the bq76930 to monitor a cell pack with a 10s1p configuration. The pack can enters (and also leave) in a special operation mode, the bq76930 switches to the SHIP Mode and after that the cell configuartion is changed. In this special mode the new arrangement of the 10s configuration is separated in two 5s configurations and connected parallel to each other. So that port VC10 is conneted with cell 10 and cell 5 and port VC5 (-b; -x) is connected with ground of cell 6 and ground of cell 1.
Can the BMS chip be damaged by this re-configuration of the pack during the bq76930 is in SHIP mode?
Tanks for your help
Marcel Bullen
  • 0
    TI__Guru 54715 points
    Hi Marcel,
    The bq76930 cannot survive such a connection. VC5X is both the power supply for the lower cell group and the negative or low side reference for the higher group. When separating the stack into 2 parallel 5S packs, VC5X cannot be both at 5S for the lower group and GND for the higher group.
    Two bq76920 could be used, each monitoring 5 cells, but a communication isolator would be needed between the devices and additional signals would need level shifting or isolation.
  • 0 in reply to WM5295
    Prodigy 30 points
    Hi TI Team,

    there is a little misunderstandig. I would like to use the bq76930 to monitor the 10s configuration of the pack. If the pack enters the special mode, the bq76930 enters the SHIP Mode and the cell arrangement is switches to a 5s2p config. When the pack leaves that special mode (First, the cells switches back in the 10s config and after that the bq76930 should leave his SHIP Mode) --> the bq76930 starts to monitore the cell configuration. In the special mode (5s2p config) the pack is unprotected/not monitored.

    Kind regads
    Marcel
  • 0 in reply to Marcel Bullen
    TI__Guru 54715 points
    Hi Marcel,
    When the cells switch from 10S1P to 5S2P, the power for the upper group goes from 10S to 5S. But there are still cells attached to the group inputs. The bq76930 can't survive in this condition. There is a common power pin at cell 5 for the top of the lower group and the bottom of the top group. That pin can't be at both voltages at the same time.
    Again 2 bq76920 could allow the desired switching. If operation is not needed while in parallel the isolator could be a level shifter which would not need to work when the voltage difference collapsed.