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BQ35100: 4 Li-MnO2 in 2 series and 2 parallel is possible?

Katsu Matsunaga
Expert 7730 points
Part Number: BQ35100
Other Parts Discussed in Thread: BQSTUDIO

Hello,

Can we use the  gauge with 4 Li-MnO2 in 2 series and 2 parallel?

If we can make it, is there any limitation to use?

thanks and best regards, Katsu

  • 0
    TI__Genius 10370 points

    Katsu,

    Yes this part can work with a 4S2P. Mn02 mode is voltage based. You will need to use the external voltage divider to feed to stack voltage into the IC. Please follow the data sheet for the setup and how to do this. There is also a reference schematic included. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    TI__Expert 7730 points

    Hi Eric-san,

    Thank you for your reply.

    I understand it is able to be used with the fuel gauge. CR123A will be used in 2-sereas and 2-parallel.

    I have a question.

    If used batteries are used, can the gauge know state of charge in % unit?

    In this case, user need to program a profile of voltage and temperature of above battery use case into a flush memory of the gauge, right?

    Do you have application note or document of design with BQ35100?

    thanks and best regards, Katsu

  • 0 in reply to Katsu Matsunaga
    TI__Genius 10370 points

    Katsu,

    If you put a used MnO2 battery in the gauge with get the correct SOH eventually since this gauge is voltage based. This issue is I assume the "New battery" command is issued, so SOH will be 100%. We only allow SOH to change by a max amount (default 2%). So if your battery is 50% it would take 25 Wake events to get there.

    The 2% is configurable, but as a note SOH can not learn up outside of the new battery command or manually unsealing and writing it.

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    TI__Expert 7730 points

    Hi Fric-san,

    let me confirm your mentioned that "So if your battery is 50% it would take 25 Wake events to get there."

    If 50% used battery is inserted, SOH will not get correct value until done 25 wake event?

    could you please explain what is Wake event?

    If one of four batteries is 50% used one, is it possible?

    basically, the gauge accept full battery to insert, right?

    Thanks, Katsu

  • 0 in reply to Katsu Matsunaga
    TI__Genius 10370 points

    Katsu,

    A wake event is every time the GE pin goes high and the gauge takes a voltage measurement to establish an SOH value. This is the only time SOH can change. 

    If you have SOH max delta set to 50% it would take 1 wake event, 25% would take 2 ect... The default for SOH max delta is 2%

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    TI__Expert 7730 points

    Hi Eric-san,

    please confirm my understanding about BQ35100

    1. Li-MnO2 can use SOH mode, SOH indicates 100% for new battery.

    2. Coulomb counter is for ACC mode, is it possible to estimate the remaining charge by accumulating the current that has flowed since initial battery installation without HOST assist?

    3. Customer need to make the battery discharge curve (or profile) then it set into BQ35100, right?

    thanks and best regards, Katsu

  • 0 in reply to Katsu Matsunaga
    TI__Genius 10370 points

    Katsu,

    1) Correct

    2) Coulomb Counter is for ACC mode, No the gauge does not have a method to estimate remaining capacity without a Host doing the math. In ACC mode the gauge only reports out charge that has been measured to be used.

    3) In ACC mode no profile is needed. SOH or EOS mode do need a CHEMID created by TI. You can manually tune the Ra table to your battery profile if you have one available. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    TI__Expert 7730 points

    Eric-san,

    Thank you for your support.

    for answer of (3),

    What is CHEMID and Ra table? I could not find these in technical document.

    What does customer prepare to get SOH on the gauge?

    best regards, Katsu 

  • 0 in reply to Katsu Matsunaga
    TI__Genius 10370 points

    Katsu,

    The chemID info is stored in the gauge. You can program a new chemID via bqstudio chemistry plugin.  The Ra table is visible in the datamemory section.

    Each specific battery will need to have its chemID created which represent the OCV and RA for that battery.

    Customer will just need to make sure the cell they are using is in the chem list. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    TI__Expert 7730 points

    Hi Eric-san,

    Thank you for your support.

    I understand about CHEMIID and Ra table.

    I have a question about mode switching.

    - At first, the gauge start up in SOH mode then measurement SOH. after that load current perform in ACC mode. Is this possible?

    Best regards,

    Katsu

  • 0 in reply to Katsu Matsunaga
    TI__Genius 10370 points

    Katsu,

    Yes this is possible, but there are two potential downsides.

    1) You need to have the device unsealed which could make it open to corruption externally (hacking)

    2) You will be writing flash so if you make the change too many times the flash can eventually wearout. 

    Also you will need to reset the gauge after the bit change. 

    Thanks,

    Eric Vos