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OMAP-L138: I2C signals momentarily drive HIGH

Neil Atkinson
Intellectual 270 points
Other Parts Discussed in Thread: OMAPL138, TPS65910

Hi

I have noticed that the I2C signals (SCL, SDA) are momentarily being driven HIGH by the OMAPL138 during a ZERO to ONE transition. Below is a capture of the SCL signal on our board.

I have seen other threads raising a similar issue:

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/381604.aspx

but I cannot find any conclusive information as to whether this is the expected behavior of the OMAP's I2C interface.

Can a representative from TI please confirm is this expected behaviour?

Kind regards

Neil

  • 0
    TI__Mastermind 43660 points
    Hello Neil,

    We are investigating on this issue internally. As of now, it seems like I2C IO buffer is designed in such a way that it produce this ringing at the beginning of low to high transition.

    I will keep you posted on this if there is an update.

    Regards,
    Senthil
  • 0 in reply to Senthilkumar Srinivasan
    Intellectual 270 points

    Hi Senthill

    Thanks for your response. Do you know when you might have some news?

    With regards to the ringing on our board, I think that this may not be a problem for us because the duration of it should be filtered by the 50ns glitch filter that I2C devices should incorporate in each of the interface lines (SCL and SDA) as part of the standard. I am currently checking that the other devices on our I2C bus support this. One of the devices we use is the TI TPS65910, but the data sheet does not mention a glitch filter. Can you confirm that this device will filter <50ns glitches and therefore ignore the type of ringing shown in the scope trace?

    Kind regards
    Neil

  • 0 in reply to Neil Atkinson
    TI__Mastermind 43660 points
    Hello Neil,

    Hopefully I would get an update in couple of weeks as most of the people are busy with other high priority tasks.

    Yes, you could use filter to reduce this effect. However, i could not comment about the filter requirement for TPS65910. There is a separate forum deals with TPS659xx parts. I would suggest you post your query over there.

    e2e.ti.com/.../43

    Regards,
    Senthil
  • 0 in reply to Senthilkumar Srinivasan
    Intellectual 270 points
    Hi Senthil

    Thanks for the quick response.

    I hope to hear from you in a couple of weeks. In the meantime, I'll continue my enquiry into the TPS65910 on the other forum.

    Kind regards
    Neil