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Communication protocol between DC fast charger and EV BMS

Kaveh Mohammad
Prodigy 110 points

Hi,

I am working on the design of an external charger for EV batteries. Specifically in case of DC fast charge: I need to know when the external charger communicates with EV BMS, what information about the EV battery is shared with the external charger. Min/Max current, Min/Max voltages, charging profile etc. so that the external charger can estimate battery SOC, define charging profile, know when to stop charging and the charging limits etc.

What standard I need to review to find the answer to the above questions. Or any helpful information is appreciated,

Thank you,

I was referred to this forum from below thread: 

e2e.ti.com/.../4622484

  • 0
    TI__Expert 8526 points

    Hi Kaveh,

    Are you able to access any of the BQ79731 documentation?  Do you have an NDA in place with TI?

    Best,

    Andria

  • 0 in reply to Andria McIntyre
    Prodigy 110 points

    No I dont have NDA with TI. I dont need details of BQ79731 chip. I just need to know the communication protocol and standards and what battery information is shared with an external charger when it connects to an EV BMS.

  • 0 in reply to Kaveh Mohammad
    TI__Expert 8526 points

    Hi Kaveh,

    The NDA is in case you will need access to the full datasheet for any questions you may have later.

    To answer your question as much as I can from the monitor IC side, the BQ79731 can pass information to an MCU.  This information includes current measurements and overcurrent faults as well as voltage measurements across high voltage nodes (voltage divided down), fuse, and contactors.

    Additionally, the BQ79731 has a coulomb counting feature that will allow for SOC estimation.  The BQ79731 coulomb counting allows for 255 cycles of stored data, or > 16 ms of data with a 64 uS conversion rate.

    I do not see anything discussing the BQ79731 communicating with a charger directly.  The information discussed above is passed to the MCU.  The BQ79731 can communicate back and forth with an MCU using UART or SPI; however, the BQ79731 GBPIO10 and GPIO11 pins can be configured for an I2C controller interface.  This allows the MCU to communicate with an I2C device through the BQ79731.  The BQ79731 acts as an I2C communication pipeline.

    To answer your question from the charger side, I will assign this thread to the chargers team, and they will answer you shortly.

    Best,

    Andria

  • 0 in reply to Andria McIntyre
    TI__Guru**** 167236 points

    HI Kaveh,

    TI Charger group doesn't have an EV charger.  Most of our chargers are I2C based, with only a few having SMBus level 1.  Customers rely on the host software as the I2C interface between battery protector and gauge.

    Regards,

    Jeff