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BQ35100: Host side Lithium Thionyl Battery Gauging

Michael Redpath
Prodigy 90 points
Part Number: BQ35100

Hi,

We have a 2-cell Lithium Thionyl batteries in series and some battery protection circuitry. This includes a fuse and some diodes.

In our application, the BQ35100 can only be mounted on the host side with the micro-controller. Would the additional protection circuitry strongly impact the BQ35100 in EOS mode?

Would the BQ35100 be the most suitable solution for this application?

  • 0
    Prodigy 90 points
    The fuse adds an additional couple of ohms and there are a number of diodes in series and some in parallel to the battery. This, I imagine, would affect the BQ35100s ability to measure the internal resistance of the battery?
  • 0 in reply to Michael Redpath
    TI__Guru* 76230 points
    WHat mode are you operating the device in? If in EOS, i don't think those additional resistances will impact much because the gauge uses the changing resistance slope to determine the EOS of the cells and not the exact battery internal resistance. Also for accumulator mode, internal resistance is of no consquence, it is only SOH mode that you may have some issues
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 90 points
    Thanks for your response.

    We would much prefer to use the device in EOS mode. You say the extra resistances should not have a significant impact. There will also be 3x Nexperia PMEG3050 diodes in series. They will cause a voltage drop that will vary depending on the current draw.

    Will the series diodes affect the device in EOS mode?

    Also, can we supply REGOUT with external 2.5V and leave REGIN floating?
  • 0 in reply to Michael Redpath
    TI__Mastermind 24870 points
    Hello Michael,

    3x Nexperia diodes seems to lead to close to a 1 volt drop. This will affect the EOS calculation, but I am not sure by how much.

    REGIN should not be left floating, it is tied to the battery. Our EVM will not boot up if REGOUT is powered and not REGIN.

    My recommendation is to order bq35100 EVMs and perhaps test the voltage drop on the accuracy of the EOS calculation.

    Thanks