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BQ27750EVM-837: BQ27750EVM-837

Danil Koshelev
Intellectual 320 points
Part Number: BQ27750EVM-837
Other Parts Discussed in Thread: BQ33100, BQ40Z50, BQ35100, BQ76920, BQ78350-R1, BQ78350

Dear TI,

1) What polynomial(algorithm) do you use in calculation of checksum at I2C bus BQ27750?

2) I'm interested in a chip with a Coulomb counter on board, protection circuits and balancing algorithm for 3 cells with a maximum limit of the counter (120000 mAh or more).
    I can see top level is - BQ33100 (Max Capacity - 65534 mAh), correct? Can you suggest a more capacitive solution (single chip is better, but multiprocessor system is also ok)?

3) if there are no other ways: is it possible to set Coulomb counter any one of your chips to each second restarting with data updating?

Thank you!
Best regards, Danil

  • 0
    TI__Genius 10370 points

    Danil,

    1) The I2C checksum can be found under command 0x60 (MACDataChecksum()) where the checksum needs to be written in the TRM. Here is a basic formula to use checksum = Byte_SUM(address, [data]) then NOT.  written out "The checksum is the 8-bit sum of the MSB and LSB of the command plus the (command length) bytes in the buffer. The final sum is the bitwise inversion of the result". In addtion to the checksum needing to be written the length is also needed, although it is not included in the summation. The length parameter instructs the gauge how many bytes to perform a similar checksum on to verify the result.

    2) Here are a few options.

    bq40z50 - Li-ion multicell gauge. Does balancing, Protections by controlling a Chg and Dsg FET, Coulomb Counting Impedance Track gauging, and more. It is 32767mAh limited, however you can adjust the calibration on the device to account for this with. 

    bq35100 - this is a gauge with a Coulomb counting only mode. It has a much higher limitation, but doesnt offer balancing and protections only coulomb counting

    Please elaborate on your needs and i can better direct you to the best solution.

    3) The bq35100 will start from 0 every time you wake it up and then if you issue a command it will commit the coulombs it counted into flash memory. Likewise you can issue a command to reset it back to 0. This part is intended for primary cell and does require some host interaction to wake it up and tell it to start counting. 

    Please let me know more info on question 2 and i can get you to the right people. 

    thanks,

    Eric Vos

     

  • 0 in reply to Vos
    Intellectual 320 points

    Hello Eric, about 2-nd question:
    1) I am intresting BQ78350-R1 with companion of BQ76920.
       Looks like:
       A) BQ76920 has measuring CC with complete BMS on board (includ balancing 3-cells parallel, fet control, protection and etc...).
       B) BQ78350-R1 has gauging alghorithm which use value reading from registers of BQ7692.

    But I see information conflict between datasheet and website.


    Please, tell me -  this supports the configuration up to 320 Ahr for 3-cells parallel?

    My task is to find a replacement for the obsolete BMC microcontroller - 120 Ahr, 3-cells parallell, Li-ion.

    Thank you, Danil

  • 0 in reply to Danil Koshelev
    TI__Guru* 76230 points
    Hi Danil,
    I would recommend you create a different post on the bq78350 so you can have your questions addressed by the appropriate team.
    thanks
    Onyx