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BQ78350-R1: SMBus clock stretching

user1650923
Prodigy 90 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQSTUDIO, EV2400

Hello

I'm sorry, my English is not good.

I am using BQ78350-R with Renesas MCU.

I observe the clock stretch which occasionally occurs in SMBUS.

The observed clock stretch is about 13 ms long.

It seems that no stop bit is generated when this clock stretch occurs.

After this clock stretch occurs, the device is reset and restoration is carried out.

Attach the observed waveform of clock stretch.

How long is the maximum clock stretch for the BQ78350-R1?

Is the observed waveform a normal waveform?

Please let me know if you have any information.

clockstretch.pdf

  • 0
    TI__Guru* 81034 points
    Hi,

    The maximum clock low time during a transaction is 25ms, so your waveform is well within this limit. I suspect that the communication problem is not because of clock stretching. I do not see an acknowledge from the 2nd byte which is the SMBus command.

    Here are a couple of things to help debug the issue:
    - Capture a few SMBus transactions using the EV2400. In bqStudio, there is a Advanced Comm SMB screen where you can run basic commands and you can capture the waveforms to compare with your transactions. Make sure to disable the Dashboard, so that SMBus is not executing constantly to update the values.
    - There is a very useful SMBus app note that explains multiple common issues. You can review this and see if it provides any clues: www.ti.com/.../slua475.pdf

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Prodigy 90 points
    Hello

    Thanks for the response.
    I understood that the clock stretch is less than 25 ms so it is not a problem.

    About acknowledge can be checked after clock stretch.
    It is characterized that clock stretch occurs between data and acknowledge.

    Before setting clock to HI, it seems to be a problem that DATA becomes HI.

    Best regards,
    user1650923
  • 0 in reply to user1650923
    TI__Guru* 81034 points
    Are you able to capture the waveform with an oscilloscope? This will show which device is driving the clock low.
    Does your MCU firmware support clock stretching?
    Is it possible the device does not recognize the SMBus command?

    If you are able to try the following (using an oscilloscope), I think it can give some good information to help debug the issue:
    - Capture a few SMBus transactions using the EV2400. In bqStudio, there is a Advanced Comm SMB screen where you can run basic commands and you can capture the waveforms to compare with your transactions. Make sure to disable the Dashboard, so that SMBus is not executing constantly to update the values.

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Prodigy 90 points

    I have been late for my less.

    Problem phenomenon has not occurred.

    >Does your MCU firmware support clock stretching?

    Yes, it corresponds.


    >Is it possible the device does not recognize the SMBus command?

    If there is a clock stretch between DATA and ACK, I confirmed that it was working.

    Does clock stretching occur between NACK-stop conditions?

    If 25ms indicates the time of one command, there may be clock stretching also in this part.

    Best regards,

  • 0 in reply to user1650923
    TI__Guru* 81034 points
    I'm sorry, I am a little confused. You say the problem phenomenon has not occurred. Does this mean you no longer observe the issue?

    Were you able to capture oscilloscope waveforms yet?

    Thanks,
    Matt
  • 0 in reply to Matt Sunna
    Prodigy 90 points

    Response is late and I'm sorry.

    The phenomenon being reported no longer occurs.

    The phenomenon occurs at a very difficult time.

    I would like to take time to tackle the problem.

    Thank you.