LMK05028: Synchronize 25MHz to 1Hz PPS signal

Prodigy 340 points

Replies: 1

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Part Number: LMK05028

Hi Experts,

My customer has a Gigabit PHY that is time synchronized using IEEE-1588. It outputs a 1 Hz Pulse Per Second. They would like to synchronize their 25 MHz system clock to this PPS signal.They plan to run our AM3359 PRU Real Time Ethernet at 8 KHz. The PRU SYNC0 signal run through a PLL on each device. This is programmed to produce a configurable clock, depending on the slave device type and conversion rates. (600KHz - 8.192 MHz). The PRU will keep the slave devices from drifting apart, but the PRU itself will drift with respect to the grandmaster time unless it is driven with a PTP disciplined clock.

I looked at the LMK05028 synchronizer clock, but I don’t have much experience with these advanced PLL chips.

Any recommendations? (Preferably small form factor)

Thanks,

Connie

1 Reply

  • Hello Connie,

    A block diagram may be helpful to me here.  I want to be sure I understand the frequency plan, you have one input and three outputs:

    1 PPS input, from Gigabit PHY synced to IEEE-1588: 1x
    8 kHz output, for AM3359 PPU Real Time Ethernet device: 1x
    600 kHz to 8.192 MHz output, PRU SYNC0 signal: 2x

    You mention one PLL for each PRU SYNC0 signal.

    * How does the PRU keep the slave devices from drifting apart?  Will it apply DCO to the PLL driving it?

    * For the 600 kHz to 8.192 MHz, is there a set of frequencies they are picking from or could it be just any frequency.  Is there any frequency accuracy requirement on these outputs?

    * If there are two PLLs for the PRU SYNC0 signal, is it ok for the 8 kHz output to share frequency domain with one of these PLLs?

    73,
    Timothy

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