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AM335x CLKOUT1 layout

weiji jiang
Expert 2040 points
Other Parts Discussed in Thread: AM3358

Hi TI Folks,

  Good day to you.

  In my design, OSC0 is 24Mhz, and configure CLKOUT1 as buffer to output 24Mhz.  I would like to see your advise on the CLKOUT1 signal layout:

1. What is the PCB stack impedance of CLKOUT1 trace? Is it 50 ohm?

2. When I layout the CLKOUT1 trace, do I need to put a resistor in series  for impedance matching purpose? If need, please advise the suitable value of resistor.

best regards

Jiang WeiJi

  • 0
    TI__Guru**** 393215 points
    Hi,

    There are no special design guidelines for CLKOUT1 layout. You can follow the general guidelines for high-speed layout: www.ti.com/.../scaa082.pdf
  • 0 in reply to Biser Gatchev-XID
    Expert 2040 points

    Hi Biser,

      Good day to you.

      Thank for your information, after that I still has some question, please adivse:

    1. The CLKOUT1 in AM3358 is single end type signal, isn't it?

    2. If we layout the CLKOUT1 using microstrip method, what is the characteristic impedance (Z0) of CLKOUT1 ? Refer to 1.3.2 in page No.6 of scaa082.pdf

    3 What is the Zsource (CLKOUT1) impedance ? Refer to Figure 5 in page No.7 of scaa082.pdf

    4. Refer to page No.7 of scaa082.pdf: A receiver often has a high-impedance input. To avoid these over-and undershoots the reflections must be reduced. Therefore, a proper termination is required.

    Please advise what kind of termination should I use, and what is the suitable value of the termination resistor.

    best regards.

    Jiang WeiJi

  • 0 in reply to weiji jiang
    TI__Guru 62855 points

    Make the trace impedance approximately 50 ohms and use a 22-33 ohm series termination resistor located as close as possible to the AM335x pin. The reflection that returns from the far-end of the non-terminated transmission line will be mostly absorbed by the series termination resistor and source impedance of the output buffer.

    Regards,
    Paul

  • 0 in reply to peaves
    Expert 2040 points
    Hi Biser,

    Good day to you.

    Thank for your information.


    Jiang WeiJi