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BQ40Z80: The issue of BQ40Z80EVM-020 SMBus waveform.

user5767698
Intellectual 350 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: , EV2400

HI:

   When i measure the BQ40Z80EVM-020 SMBus waveform,i found the wave on SDA was abnormal,the waveform as follows,SDA waveform with a spike，what are the causes of this? 

  • 0
    TI__Mastermind 42535 points
    Hi,

    Can you please confirm that you are using the bq40z80 evm? The pulse seems spurious and has definitely lasted less than one clock interval, so it should not affect readings. Did you have any EMI source nearby? Noise can definitely be injected from the environment into the board by coupling.

    One easy test you can do is connect the evm and put it in a mylar bag and then see if you still get these weird pulses on the comm lines. It's a cheap way to test it if you have access to one.
  • 0 in reply to Batt
    Intellectual 350 points

    Thanks for your reply.

    Yes，i using the  bq40z80 evm，the test  testing environment as follows，i don't think the pulse caused by EMI source.It just a power source nearby，according to your suggestion， i measure the waveform on the SDA lines  again， the waveform same as before.Do you have the bq40z80 EVM?Measure the BQ40Z80EVM-020 SMBus waveform and show us the waveform if you can.Tahnks for you support.

  • 0 in reply to user5767698
    TI__Mastermind 42535 points

    Thanks for the screenshots and the image. I'm going to take this to the hw developers and find out the reason for this. Please allow me a week to get back to you. I will most probably take less time than that to get back to you.

    In the meanwhile, do you by any chance have an external EV2400 box? If yes, can you please communicate to the gauge using that instead of the on board device? This is just to isolate any electrical issues that might cause it.

  • 0 in reply to Batt
    Intellectual 350 points
    I use an external EV2400 box communicate to the gauge，the waveform on the SDA lines same as before.My own PCB board also have this problem.
  • 0 in reply to user5767698
    TI__Mastermind 42535 points
    I see that you are actually using the internal ev2400 onboard the evm. In your PCB, is the IC being directly mastered by the host? If it's possible, can you send me screenshots of the full transaction where this happens? A logic analyzer data dump would also be useful if you can send it. The reason for this is, I'm trying to figure out if it's the host, gauge, or a line glitch.
  • 0 in reply to Batt
    Intellectual 350 points
    In my PCB,the gauge is directly mastered by the host,the waveform same as bq40z80 EVM,the pulse appeared in the same location.I think it may be caused by the gauge.The other users have this problem?You can verify this by measuring the BQ40Z80EVM-020 SMBus waveform. Looking forward to your reply.
  • 0 in reply to user5767698
    TI__Mastermind 42535 points
    I will try that. However, can you please send me the full transaction of where this happens. Your scope shows zoomed in data. I just want to see where it is that the data line does this.
  • 0 in reply to Batt
    Intellectual 350 points

    Thanks for your replay.The pulse appeared in the ninth clock.When you  measuring the BQ40Z80EVM-020 SMBus waveform have this problem?

  • 0 in reply to user5767698
    TI__Mastermind 42535 points
    Thank you. I will check this out and reply here.
  • 0 in reply to Batt
    TI__Mastermind 42535 points
    I checked with fw and systems. We are able to reproduce the pulse on the evm here. That being said, this is not an issue.

    What we see is a small delay in the gauge taking control of the line. SDA going up and back down is during the low period between the 8th and 9th clock pulses, that just looks like the delay in the hardware after the clock goes low before we take control of the SDA line. In this case the master releases SDA at exactly the same time as SCL is low, and we grab it a short time later. Between those two points the pullups will pull the line high.
  • 0 in reply to Batt
    Intellectual 350 points
    I see.But how can we remove this delay? The 9th clock is ack signal，will it affect the communication quality？
  • 0 in reply to Batt
    Intellectual 350 points
    Thanks for your help.
  • 0 in reply to user5767698
    TI__Mastermind 42535 points
    It's not going to affect comm quality. It simply shows that the master is releasing the line slightly before the gauge takes over. It's not a glitch in the system so you don't really have to worry about it.
  • 0 in reply to Batt
    Intellectual 350 points
    OK，thanks for your support.