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AM625-Q1: crystal accuracy

Jens G
Expert 3405 points

Part Number: AM625-Q1

Tool/software:

Hi team,

If they using the 50MHz clock RMII and the out clock from AM625x connected to the ETH PHY. Can the reduce also the accuracy from the crystal down to 100ppm?

 

Not sure if this is excluded in the word “derived” clock.

 

 I would assume in that case the +/-100ppm are good enough. Please can you confirm?

Thanks

Jens

  • 0
    TI__Guru 63605 points

    No. The 50PPM limit is defined in the RMII and RGMII industry standards, and the AM62x devices were only designed to operate within these limits when using RMII or RGMII.

    Regards,
    Paul

  • 0 in reply to peaves
    Prodigy 30 points

    Hi team

    In the datasheet of Phy. there is stated "Device can tolerate a 100 ppm crystal in RGMII/RMII mode,..."
    We are planning to use the RMII-clkmode of the Phy. In this mode the external 50 MHz REF_CLK is used to clock the entire Phy.

    I would assume that because of clocking the MAC and the Phy. by the same clock that there is no danger of for example a FIFO overrun.

    Could you please state if +-100ppm are good enough under the condition stated above.

    Best regards
    Friedrich

  • 0 in reply to Friedrich Wieland
    TI__Guru 63605 points

    Operating the PHY with a clock that has 100 PPM accuracy would violate the industry standard. Therefore, this is not supported. We only support a reference clock that has 50 PPM accuracy. The 50 PPM limit must include the initial accuracy of the clock source as well as the temperature variation and aging.

    Regards,
    Paul