• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 376 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ76PL455A: isolation of daisy-chain

Tamás Kolb
Prodigy 30 points
Part Number: BQ76PL455A

Dear Team,

I'm investigating the technical concept of using this chip as a BMS slave in a 650V battery pack. There are 5 battery modules in a pack. There are 32s cells in a module. There are 2 BMS slaves per module, each monitoring 16s.

I only see the Daisy-chains are separated with capacitors between the Slaves in the datasheet. I have seen other BMS Slaves using transformers instead of capacitors when separation is needed between 2 PCBs.

Do we not have this EMI concern with the differential UART and FAULT lines? Is the transformer necessary in harsher EMC environments? Do you have any appnote for this?

I have also seen differential line termination in other BMS Slave datasheets matching the twisted pair characteristic impedance. What is the rationale behind not mentioning it in the case of BQ76PL455A? Can you provide a maximum length of the daisy-chain for this differential UART and FAULT communication until termination is not necessary?

Also, is it by any means possible connecting the first and the last slaves on the chain directly together to form a circle on the Daisy-chain, so if cut anywhere, the communication still possible in the other direction?

Regards,

Tamás Kolb

  • 0
    TI__Genius 14890 points

    Hello Tamas,

    You should consider looking at the BQ7961x family of devices. They have features similar to what you are requesting. https://www.ti.com/product/BQ79616-Q1?keyMatch=BQ7961

    UART and FAULT lines are same-PCB communication, so we have not had problems with EMC. For the daisy-chain interface. Take a look at the datasheet section 8.1.2.2.x . This describes how to do transformer isolation for twisted pair cables, and capacitive isolation for same PCB communications. We have tested 3 feet worth of cabling, but it is possible to go further. Yes, you can connect the first and last slave on the daisy-chain for open cable conditions.

  • 0 in reply to Alexander Scheuermann
    Prodigy 30 points

    Hello Alexander,

    Thank you for your answers. Did you mean daisy-chain ring topology possible for BQ76PL455A as well?

    In it's datasheet it says, COMMH transmitter and COMML receiver cannot be disabled. For me it means, if I connect lowermost Slave COMML to topmost Slave COMMH to form a ring topology, the topmost Slave will always echo back everything to the lowermost Slave that will cause a continuous echoing in the ring. Isn't that the case?

    I requested the detailed datasheet for BQ7961x but so far the approval did not went through. Can I receive the datasheet in an other way from you?

    Regards,

    Tamás

  • +1 in reply to Tamás Kolb
    TI__Genius 14890 points

    Tamas,

    Yes, you can do that with the BQ76PL455A. When you address the devices, you are assigning their position in the stack. This will prevent the echo-ing that you mention. If you lose communications, then you will need to reverse the stack to receive data once again.

    As for the BQ7961x datasheet. I've granted you access to the MySecure folder, so you should be able to view the full datasheet now. The BQ7961x family is very similar to the BQ76PL455A, but we've made several improvements. You can think of it as the current generation battery management product, where the 455A was the previous generation product.