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BQ76PL455A-Q1: Daisy chain signals deterioration

Massimiliano Turco
Prodigy 10 points
Part Number: BQ76PL455A-Q1
Other Parts Discussed in Thread: BQ76PL455A, BQ79616

Hello, we have communication troubles with the last BQ76PL455A-Q1 of a chain of 13 devices.

In a first time we had no communication at all just with this device but reducing the cables capacity (changing size, type and length) we reduced the problem. Now we have good communication but randomly we start to see errors.

We would like to understand if there is a way to evaluate the signal deterioration. We are looking at the COMM+/COMM- with an oscilloscope and we can see difference in voltage level and timing between the exit of the different boards, but we cannot understand if the signal is good enough. There are min/max voltage level or threshold? Minimum timing for low and high state or other parametesr to look at?

Here after 2 immages of signals comparison.

Thanks a lot

  • 0
    TI__Genius 17370 points

    Hi Massimilano,

    The bq76pl455a device does not reclock the daisy chain signal between each device so I would say it may start to deteriorate with more than 6 devices in a stack (depending on cable used and pcb design and noise). Would you consider using our newer bq79606a or bq79616 devices which reclock the signal across each device which make it more robust for large stacks? Otherwise I recommend creating two separate stacks of 6 to alleviate potential signal quality issues.

    Regards,

    Taylor 

  • 0 in reply to Taylor Vogt
    Prodigy 10 points

    Hi Taylor, thanks for the reply.

    At this stage of our project is difficult for us to move to another device or to split the stack. We are working on moving on the new device for future project but it is not comliant with the timeline of the actual one.

    So we would like first of all to try to keep the stack like it is and workning on the cables. For that reason I would like to ask you if there is a way to evaluate the signal, by looking at the waveform. 

    Thanks

  • 0 in reply to Massimiliano Turco
    TI__Genius 17370 points

    Massimiliano,

    I can point you to section 6.18 of the datasheet for several parameters but I don't believe we provide higher detail for this device since it can depend on pcb design, external components used etc. So if you see issues, I recommend reducing the devices on the stack or experimenting with the component design.

    Regards,

    Taylor