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CLKOUT2 for Ethernet/EtherCAT Phys

Bernd Sprenger
Intellectual 340 points

Part Number: AM4377
Other Parts Discussed in Thread: DP83848K

Hello,

we are designing a board with the AM4377 as an EtherCAT slave. In the technical reference manual SPRUHL7I on page 187 there detailing the bootstrap option, there is writte "SYSBOOT[18] can be used to supply a clock for external ethernet PHY devices" (CLKOUT2 will be configured to deliver the 25MHz/50MHz clock for MII/RMII). Our design will use the DP83848K as Phys and we would like to make use of the CLKOUT2 to provide the 25MHz by the using the internal EXTDEV_PLL. Our system runs from a 24MHz OSC0 crystal with 7ppm stability.

We made a review with an external specialist for designing SOM-modules and they are very cautious about using the 25MHz generated by the AM4377.

Since I couldn't find any specifications, is the jitter of the EXTDEV_PLL good enough for providing the 25MHz clock for 100MBit Ethernet/EtherCAT when providing the 24MHz clock by a 7ppm crystal? Do you know of a successful usage of the CLKOUT2 to clock a 100MBit Ethernet/EtherCAT PHY?

Thanks a lot for your help,

have a nice day,

Bernd

  • +1
    TI__Mastermind 27890 points

    Hello Bernd,

    The jitter of this output clock has not been fully characterized by TI and as such I would be hesitant to recommend it for your use-case. I have not seen an implementation such as the one you are describing.