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Original question:

HDC3022: I2C standard mode

HDC3022: Question about tR/Tf of IC Interface Timing.

Kazuya Nakai59
Guru 21715 points
Part Number: HDC3022


Tool/software:

Hello guys,

One of my customers is evaluating HDC3022DEJR with I2C fast mode (400kHz) for their new projects.

At this moment, they have the following question.
Could you please give me your reply?

Q.
HDC3022 SDA/SCL rising(tR) and falling(tF) time on their board are faster than 20ns
because SCL is driven by push-pull CMOS output and SDA is driven by 3 state push-pull CMOS output. 
as only HDC3022 and one controller are connected to I2C communication line.

Is it no problem that SDA/SCL rising(tR) and falling(tF) time are faster than 20ns?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Genius 12855 points

    Hello Kazuya,

    That will not be a problem. The HDC302x uses voltage thresholds (VIL & VIH) to determine the state of SCL & SDA on the pins, not rise and fall time. As long as you are able to read/write correctly, then it is OK.

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Guru 21715 points

    Hello Alex,

    Thank you very much for your reply.

    I understand that it is not a problem if the SDA/SCL rise time (tR) and fall time (tF) are faster than 20ns.

    Could I ask you additional questions as the follows?

    Qs.
    6.6 I2C Interface Timing table on page 9 of HDC302x datasheet says
    that the minimum tF(SDA,SCL fall time) and tR(SDA, SCL rise time) for FAST MODE are 20ns.
    I thought that these tr/tf were the recommended operation condition for SDA/SCL input signal timings.
    1. Is my thought not correct?
    2. Is it not necessary to follow this minimum time (20ns)?

    Your reply would be much appreciated.

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Genius 12855 points

    Kazuya,

    Yes the 20ns is a conservative limit, the sensor can support much faster rise and fall times. You do not need to follow the 20ns limit. 

    Thank you

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Guru 21715 points

    Hello Alex,

    Thank you very much for your strong supports.

    Could I ask you similar questions again because the customer wants to confirm TI’s answer.

    Qs.
    The I2C specifications can be found at the following URL.
    www.nxp.com/.../UM10204.pdf
    The tr/tf timing information are on page 44 of these specifications.
    The minimum tr/tf valued of HDC3022 data sheet are described in the specification.
    Q1.
    This is the same as the previous question.
    Is it no problems for I2C communication if tr/tf is 20 ns or less?

    Q2.
    Will there be any problems if tr/tf is 3 ns or 5 ns as long as there is no noise on the waveform?

    Your reply would ne much appreciated.

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Genius 12855 points

    Kazuya,

    Our numbers in the HDC3x datasheet come from that I2C spec. However our devices are capable of much better performance. I think 3-5ns rise/fall time would be fine.

    Regards

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Guru 21715 points

    Hello Alex,

    Thank you very much for your strong supports.

    They understood your answer. 
    Thank you again.

    They have additional questions about HDC302x. Is it okay to ask you it in this thread?
    If it's better to ask in a new thread, please let me know.

    1. As the following URL thread says, they believe HDC302x also works with I2C standard mode.
       Is their thought correct?

    https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1395031/hdc3022-i2c-standard-mode?tisearch=e2e-sitesearch&keymatch=HDC3022#


    2. They think the difference between I2C standard mode, fast mode, and fast mode + is data communication speed only.
        Also they think the method and content of data transmission are the same except timing requirement spec for each mode.
        Is their thought correct?

    Could you please give me your reply?

    Thank you very much and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Genius 12855 points

    Kazuya,

    1. Yes the HDC302x works with I2C standard mode as well.

    2. They are correct, the different I2C modes differ only in communication speed. All read & write transactions will be the same, just done faster or slower.

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Guru 21715 points

    Hello Alex,

    Thank you very much for your reply.

    My customer questions were solved.

    Thank you again and best regards,
    Kazuya.