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BQ76PL455A-Q1: Issue related to multistack communication with >3 boards

Vikram Jain74
Prodigy 160 points
Part Number: BQ76PL455A-Q1
Other Parts Discussed in Thread: BQ76PL455EVM, ALP

Hi All, 

I am using bq76pl455 for monitoring cell voltages of multistacked modules there are around > 10 boards that are stacked in daisy chain format. Max number of boards are less than 16. 

The issue i am facing is that when i have >3 boards and attempt to read stored data from the 4th board, either i don't get a response from the bq device or the data is corrupted or there is a unknown/ unexpected delay in between the string of bytes transmitted.

This issue is somehow partially improves by setting the TXHOLDOFF bit in the IC, but setting this value to >8 bits of delay still doesn't resolve

Can someone please help me understand what all things needs to be taken care in software for stacked communication for upto 14 BQ devices connected in daisy chain. 

I have also attached the scope trace of the delay between the packets that i am noticing and an example of a good packet. 

You help will be really appreciated. 

Attached images are 2 bad response from 4th Module and 1 good response from the same module 

Kind Regards 

Vikram Jain

  • 0
    Prodigy 160 points
    Can someone please help ?
  • 0 in reply to Vikram Jain74
    TI__Genius 11480 points

    Hi Vikram,

    Apologies for the  delayed response.

    I am working with your local FAE offline to resolve this issue,  so I am going to  mark this thread as closed to  maintain a single communication line.

    One comment - I see a lot of  cross talk happening in those waveforms, as well as overshoot. This  may  hint towards a  long return path for  the signal. If would recommend probing various supply rails of the pl455 and looking for ones that are noisy- VDIG is one that  may be of interest.

  • 0 in reply to David Wiest Jr
    Prodigy 215 points

    Hello,

    I have same problem. The TX of BQ76PL455 is very noisy. Is there any way to solve this issue?

  • 0 in reply to Caner Alp
    TI__Genius 11480 points

    Hi Vikram,

    Is the communication still working properly?

    Is this on an EVM or your own board? If your own, could I check the layout?

    The probe may also have a long GND loop. Try scraping away some soldermask next to the signal and wrapping a small, stiff piece of wire around the tip of the probe to shorten the GND loop on the probe. This will usually clean up a signal that appears noisy, but in reality it is an artifact of the probe.

  • 0 in reply to David Wiest Jr
    Prodigy 215 points
    Hi David,

    This is Caner :)

    Im working on BQ76PL455EVM, Im using F28069 mcu, Im able to send data and get the response from BQ, Unfortunately Mcu cant receive all the data correctly, I tried many uart configuration on C2000 but no success. And I made sure that mcu can receive data from other C2000 Launchpads.

    So the only reason I think, the noise of the signal.

    Regards,
  • 0 in reply to Caner Alp
    TI__Genius 11480 points
    Hi Caner.

    Oops! I apologize - I must need more coffee this morning :)

    Can you put a logic analyzer on the traces? This will be helpful.

    I would still recommend probing it with a clean scope GND. At the moment, this is my best guess.

    Can you expand on what kind of data you are getting back? I would also make sure the baud rates match up. The pl455 default is 250k - try making sure that the MCU is starting at 250k as well.
  • 0 in reply to David Wiest Jr
    Prodigy 215 points
    Hi David.

    It is okey :).

    I actually solved my problem yesterday night. I was supplying BQEVM from F28069M-LAunchPad. I realized that the launchpad can't supply enough current to BQEVM.

    Another issue I realized on F28069M-Launchpad is that The board was getting too hot, I found that the inductor L6 for step up converter U12 gets too hot ( even burnt my finger). I have a few same launchpads, the issue was same on all boards. I desoldered those components, everything just works fine.

    Thanks for your help David.

    Regards,

    Caner ALP
  • 0 in reply to Caner Alp
    TI__Genius 11480 points

    Hi Caner,

    Good find! This makes sense.