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CDCM9102: Does it suport External Oscillator input ?

Guru 14465 points

Replies: 6

Views: 160

Part Number: CDCM9102

Hi,

I have questions about CDCM9102.
My customer are planning to use CDCM9102 as PCIe clock generator.
They have following questions:

Q1.
Does CDCM9102 support external oscillator input(3.3V)?
Or does it only support crystal input?
If external 25MHz oscillator input(3.3V) is supported,
are there any constraints and recommended conditions to input 25MHz oscillator externally?

Q2.
In CDCM9102 datasheet(SCAS922A) page.4, it seems that the "TYPE" of folowing signals are not correct.
- OE : TYPE is O
- OS1: TYPE is O
- OS2: Type is O
Aren't they Input pins? Is it typo of datasheet?

best regards,
g.f.

  • Hi g.f.,

    A1. CDCM9102 can support an oscillator input. Please review these related posts:
    e2e.ti.com/.../313757
    e2e.ti.com/.../684434

    A2. Yes, this is a typo and these are input pins. We will correct it in the next datasheet revision. Thank you for pointing it out

    Kind regards,
    Lane

    ____________________________________________________________________________________

    To design your own Clock Tree solution, visit WEBENCH Clock Architect ​​​​

    More information Clock and Timing System products: http://www.ti.com/clock-and-timing/overview.html

  • Guru 14465 points

    In reply to Lane Boyd:

    Hi Lane,

    Thank you for the reply.
    I understood that input from external oscillator is supported in CDCM9102.
    But I'm little confused about information in "CDCM9102EVM Clock Evaluation Module User's Guide".
    In page.4 "5.2 Configuring a Single-Ended Input", it said as follow:
    **************************************************
    For an external clock, set the input signal swing to
    2.5V (and not 3.3V, as the input is only compatible with 2.5-V input signals),
    and set the input signal frequency to 25 MHz.
    ***************************************************
    My customer are planning to input clock from 3.3V 25MHz oscillator.
    From above information, it seems 3.3V input is uncompatible.
    Is above information only related to EVM and is 3.3V OSC input available?

    And I have additional question.

    Q3.
    Are there any recommended specification of external Oscillator?

    Q4.
    CDCM9102 are implemented on AM5724 IDK EVM and CDCM9102 are supplied 25MHz
    directly from output of external oscillator.
    Do I need to place any component between XI of CDCM9102 and output of external oscillator?

    best regards,
    g.f.

  • Guru 14465 points

    In reply to Lane Boyd:

    Hi Lane,

    I posted additional question.
    Could you please reply to the above questions?

    best regards,
    g.f.
  • Guru 14465 points

    In reply to g.f.:

    Hi Lane,

    I am cleared about the clock input of EVM.
    In EVM, clock input line was AC coupled so that is why 3.3V are incompatible.

    I still want to know about Q3.
    Are there any recommended specification of external oscillator?

    best regards,
    g.f.
  • In reply to g.f.:

    Hi g.f.,

    Short the AC-coupling capacitor to DC-couple the 3.3V LVCMOS clock

    A3. The external oscillator minimum recommendations:

    • Swing: 2.5 V ± 30%
    • Duty cycle: 40% to 60%
    • Input slew rate: 0.75 V/ns

    A4. No, it is not needed

    Kind regards,
    Lane

    ____________________________________________________________________________________

    To design your own Clock Tree solution, visit WEBENCH Clock Architect ​​​​

    More information Clock and Timing System products: http://www.ti.com/clock-and-timing/overview.html

  • Guru 14465 points

    In reply to Lane Boyd:

    Hi Lane,

    Thank you for the reply.
    I understood.

    best regards,
    g.f.

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