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SN65C1167: Asking for the SN65C1167 driving capability support

SHH
Mastermind 32206 points
Part Number: SN65C1167
Other Parts Discussed in Thread: SN65C1168

Hi Team,
My customer would like to evaluate to use SN65C1167.
The SPI mater to slave trace length is 18 inch.

Please help for the three questions.
1.does SN65C1167 has the capability to drive 18" inch length? Need two chip or one chip?
www.ti.com/.../slyt441.pdf
2.Application note page 3 Rf/Cf do not disclose the vlaue. Do you have more specific reference design for my customer?

3. What is the SPI speed this structure can support?


Thanks,
SHH

  • 0
    Guru 317370 points

    While RS-422 would work, it's overkill for an 18" line.

    See Comparing Bus Solutions (SLLA067). If general-purpose logic is too weak, or if the environment is very noisy, consider LVDS.

    SPI uses general-purpose logic signals. Anything else would require both a transmitter and a receiver chip.

  • 0 in reply to Clemens Ladisch
    TI__Guru 62920 points
    Hi SHH,

    I agree with Clemens that the SPI interface may be able to drive the 18-inch PCB trace directly without requiring differential conversion, but I can also confirm that this would be no problem for the SN65C1167 device. You would need two chips - one SN65C1167 to drive the signals and one SN65C1168 to receive them. These devices have fast enough differential rise/fall times to support communication up to 20 Mbps.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    TI__Mastermind 32206 points

    Hi Max,

    Thansk.
    In www.ti.com/.../slyt441.pdf, there are Rf/Cf  in application note page 3. However, it do not disclose the vlaue. Do you have more specific reference design for my customer?

    Thanks,

    SHH

  • 0 in reply to SHH
    TI__Guru 62920 points
    Hi SHH,

    These components form an optional low-pass filter that can be used to attenuate high-frequency noise if needed. You would need to set these components so that the corner frequency, 1/(2*pi*R*C), is far above the frequency of the data being transmitted. You should also take care that the series resistance is not high enough in value that the logic signals are attenuated (since a voltage divider is formed between this resistance and the input resistance of the device receiving the signals).

    A common approach is to have pads for these components, but by default leave RF at 0 Ohms and CF uninstalled. That way, the boards can be reworked later if noise is an issue.

    Max
  • 0 in reply to Miguel Robertson
    TI__Mastermind 32206 points

    Hi MAx,
    Thanks. I will communicate with customer.
    Thansk,
    SHH