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AM3358 Internal I/O supplies

GeoD
Intellectual 325 points
Other Parts Discussed in Thread: AM3358, TPS65910

Hello,

I am using TPS65910 for the AM3358. All the supplies for the IO domain (VDDSHVx) are set to 3.3V  operation. Take as an example the Ethernet RGMII2 that uses the VDDSHV5. Am I right to assume that is ok to connect my Ethernet PHY directly to a 3.3V supply that is generated from an LDO on my card and not using the VDDSHV5 as long asd the voltage levels is the same? Any recommendation for the layout in this case?

Thanks.

Yu-Li

  • 0
    TI__Guru**** 393215 points
    Hi Yu-Li,
     
    Yes, you can use a separate power source for the PHY, as long as the interface voltage levels are the same. I don't understand what recommendations you need for layout - this is board dependent. Try to keep the Ethernet interface lines as short as possible.
  • 0 in reply to Biser Gatchev-XID
    TI__Guru**** 393215 points

    Hi Yu-Li,

    A further clarification has come in from the AM335X team:

    Keeping the Ethernet signals short may not be a good answer for all Ethernet PHYs.  Customers need to perform timing analysis using input setup/hold requirements and output delays of each device (AM3xxx and Ethernet PHY) along with any PCB delays to determine if all timing parameters are being satisfied.
     
    There is also a requirement of keeping the two supplies at the same voltage while they ramp-up and ramp-down so that one device does not source a input voltage greater than the respective VDD + 0.3 volts.