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Original question:

BQ79731-Q1: BQ79731 Serve as MSPI

BQ79731-Q1: Daisy chain device application circuit

Paul Antunes
Intellectual 2590 points
Part Number: BQ79731-Q1

hello BMP team,

my customer is designing new gen of BMS. They plan to use BQ79731 on BJB board, MCU would be located on different board. 

in typical application of datasheet, bq79731 and bq79600 daisy chain com lines COMHx and COMLx are all connected. customer won't use the H and L lines, not needed for his application.

does the BQ79731 device support com over COMLx pins only ? or is it required to connect COMHx pins as well. Note that ring feature is not required by my customer.

thank you

Paul

  • 0
    TI__Intellectual 1345 points

    Hello Paul,

    What BQ parts is your customer using? Could you please draw a block diagram of the whole BMS system so I can better understand better their layout? In the meantime, I would like to highlight the three options for communication on our 731 device:

    1. The VIF interface. For this you would connect the 731 pins to the 600 and/or the 718 via the COMH/L pins

    2. The SPI interface: You can use the SPI pins on the 731 device to communicate directly to the MCU with no 600. For this option, you cannot stack any cell monitors (71x devices)

    3. The UART interface: You can use the TX/RX pins on the 731 device to communicate directly to the MCU with no 600. For this option, you can also communicate to 71x devices via VIF

    Thanks!

    Best,

    Abigail Bueno.

  • 0 in reply to Abigail Bueno
    TI__Intellectual 2590 points

    hello Abigail,

    i have no design files to share from customer at this stage; we are in pre-desgin phase where customer is defining the architecture. 

    Let me re-phrase the question from the customer:

    In datasheet of BQ79731, there is daisy chain application circuit (see attached screenshot) with COMHP/N and COMLP/N connected to BQ79600.

    My customer wants to know if BQ79731 can be connected to BQ79600 using COMLP/N lines only (and leave COMHP/N pin unconnected) ? 

    Rest of BMS system is using wireless interface. Only BCU (with BQ79600 on it) and BJB (w/ BQ79731) are connected over daisy chain. There is no need for ring just in case you are asking the question.

    thanks

    Paul 

  • +1 in reply to Paul Antunes
    TI__Intellectual 1345 points

    Hello Paul,

    Thank you for clarifying. Yes, you can leave the COMHP/N pins unconnected. The ring architecture is someting that we recommend but it is not necessary for your set up.
    Additionally, please note that the communication pins should be connected as follow:

    • North direction (Default): COMHN/P pins of 600 → COMLP/N of 731

    Communication can be done the other way around (south direction), you will then need to connect COMLP/N of 600 --> COMHP/N of 731. Meaning that the configuration should always be a high going to a low, or vice versa. 

    I hope this information was helpful.

    Best,

    Abigail Bueno.