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LMK05318: Is there a clock chip that can operate without an XO oscillator?

Istvan Nagy
Prodigy 30 points
Part Number: LMK05318
Other Parts Discussed in Thread: LMK05028, , LMK03318, LMK5B12204, LMK03328, CDCE6214

I was told that the LMK05028 require two input oscillators, that is one too many. 

It also requires the second oscillator connected at the XO pin to be in a 48...54MHz frequency range.

I cannot find any purchasable oscillator in that range that also provides <0.3ps RMS jitter. There are parts with 1...3ps jitter, but those are not usable in my application.

156.25M oscillators are readily available with <0.3ps jitter from multiple vendors.

So, is there any LMK clock chip that can run from a single 156.25MHz oscillator, have low jitter, EERPROM and fractional PLL? 

Any of these can operate with XO disconnected? LMK05318, LMK03318, LMK5B12204...

  • 0
    TI__Genius 12380 points

    Istvan,

    You could potentially use the LMK05028 with the same reference input to both oscillator inputs, but you would have to potentially worry about signal integrity.

    For 8 outputs from a single reference, the LMK03318/LMK03328 may be suitable - using a single XO on SECREF is sufficient for operation. However, it will lock to a lower frequency if the single output is disconnected - with a 25 MHz input and 125 MHz output, the locked output frequency with the reference disconnected is anywhere between 114 MHz and 124 MHz (although most often one of those two extremes).

    For 4 outputs, the CDCE6214 is available - with a 25 MHz input and 125 MHz output, when the input is removed, the output locks consistently to 118.5 MHz.

    For true holdover, I believe that you will need one of the network synchronizer devices used as a clock generator - I will get back to you shortly on this.

    Thanks,

    Kadeem