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  • TI Thinks Resolved

LMK05318: Schematics of LMK05318 clarification required for XO input & the oscillator Part selection & its filter design

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Replies: 3

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Part Number: LMK05318

ti review.pdf

  • Hello,

    Please allow a few days to reply for this request.

    Thank you,

    Liam Keese

    Clock and Timing Systems & Applications


    To view training videos on Clock and Timing Solutions please visit  TI Precision Labs ​​​​

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

  • In reply to Liam Keese:

    Hi Liam,
    Thank you for the update.
    Herewith in this thread I am attaching the latest Schematics files for your review.5187.ti clock section_latest.pdf
    Kindly update me as soon as possible as we have to release this board design to Fab house by Tuesday.
    Appreciate your timely help so much.
    My actual query as below:

    I am designing a board that uses the TI LMK05318RGZT part. In the data sheet of this part, it is mentioned that to feed the XO with single-ended LVCMOS clock voltage up to 2.5 V can be applied to the P input with the N input pulled down to ground.

    But in the Typical application Reference schematics in data sheet Page No 69, figure 64 it is mentioned for 'Y1' with the part 8W48070002 feeding the XO input. This part is supplied with 3.3V & the output voltage levels

    of this Oscillator are not meeting the Input voltage requirement of IC LMK05318. Maximum of 2.6 VPP can be applied to the input of the XO_P input. But this oscillator Y1 feeds more 90% output voltage level of supply voltage(3.3V here). so, it comes 2.97V exceeding the 2.6V.

    Is not that a issue?

    Also, in the reference application schematics, the filter combination of 100 ohm series resistor + 0.1uF cap + 49.9 Ohm resistor + again 0.1uF capacitor is present at the output of Y1. This makes me confusing as why this much double coupling & filtering & termination.

    So, attached herewith is my schematics design using LMK05318. and used different oscillator than the one present in Reference design because of RoHS3 compliance info missing for that part.

    Please confirm my oscillator part selection & the filter design used at the output of the oscillator in y design.

    Also, review the schematics & share your comments.

    Thanks & Regards,

    Sathiya Seelan Sekar

  • In reply to Sathiya Seelan Sekar1:

    Hi Sathiya,

    Yes the internal capacitors will be stressed if the CMOS input at XO is higher than 2.6V. The two AC coupling capacitors are actually not needed because there is internal AC coupling. The 100Ohm and 50Ohm form a resistor voltage divider to divide down the 3.3V. I saw that you already used the recommendation in figure 29 of datasheet and that's good.

    Regards,
    Hao

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