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BQ79614-Q1: Single Transformer Isolation between two BQ79614-Q1 on the same PCB

Part Number: BQ79614-Q1
Other Parts Discussed in Thread: BQ79616-Q1

Hi TI,

I was wondering if there would be any troubles/drawbacks on using transformer isolation with a single transformer between two BQ79614-Q1 on the same PCB. The interface between trasformer and BQ would be the same on both primary and secondary (from each BQ POV: termination, Cypass, Rseries, ESD, Cbypass on center taped transformer).

What do you think/suggest?

Many Thanks

Fatjon

  • Hello Fatjon,

    Typically if a customer is doing daisy chain on the same PCB, they use the capacitor & choke isolation. I haven't seen anyone use a single transformer, so I don't have any data on if this would work. As long as you are meeting the eye diagram in the BQ79616-Q1 Daisy Chain Communications Application Report, then the communication will be successful.

  • Hi Alexander,

    Thank you very much for replying!

    Apparently there is no need to isolate with transformer inside a PCB, but this is a case where hot-plug related problems could happen and the purpose is to avoid capacitive coupling (if that would be an issue) between side by side BQs. Battery modules can contact in the same time. I'm not worried that much about eye diagram, just a matter of electrical stress during hot plug. 

    My doubt was about any hypothetical issue about interfacing with only one center taped transformer, even though in theory there shouldn't be any problem. What do you think?

    We can afford a trasformer based isolation between two BQ but 2 transformers would be a problem also for available space in the PCB. 

    Please tell me if anyone had similare experiences of hot plug with BQs or similar battery monitors.

    Many thanks for your support!

    Fatjon

  • Fatjon,

    Hotplug is always a concern with battery packs. I don't think there is any issue with your transformer suggestion, however you will need to test it to make sure there is no errors in communication in the normal use case.

    In general our customers are using the capacitor and choke isolation on PCB daisy chain connections. Here are two suggestions that other customers have implemented to help with hotplug and ESD:

    1) Carefully select the ESD diode on the COMMx pins. PESD1CAN,215 is what is on our EVM, however for extra protection, we recommend a lower clamping voltage such as the PESD15VL2BT,215

    2) You can capacitively couple the PCB ground planes together. 2x 4.7nF capacitors like the image below will help prevent ground bouncing during hotplug. GND1 means the ground of the first BQ7961x device and GND2 means the ground of the second BQ7961x device when they are both on the same PCB.