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SK-AM69: PCIE SMBus voltage

John Eubanks
Prodigy 61 points

Part Number: SK-AM69

Tool/software:

The SK-AM69 uses a voltage translator (TCA9543APWR) on the SMBus connected to the PCIe Card Slot on page 37 of the schematics (Rev. E3).

Is this necessary?

I thought the SMBus on a PCIe slot uses 3.3V logic signals, not 1.8V.

  • 0
    TI__Guru 55005 points

    The SMBus standard support ranges that include both 1.8V and 3.3V IO.  For SMBus on the PCIe interface - I'm not completely sure (I don't have the full PCIe specification).  I do have a PCie M.2 spec - and it shows for SSD drive, the SMBus interface is 1.8V.  

    My recommendation is to look specifically at the PCIe peripherals that might be used in your design and see what SMBus voltage they require.

  • 0 in reply to Robert Eschler
    Prodigy 61 points

    Yes, I think the PCIe M.2 card is a different voltage than the full-size PCIe edge card slot.

    The PCI Express Card Electromechanical Spec Rev. 3.0 states the following pertaining to the SMBus:
         "The system board provides pull-ups to the +3.3Vaux rail per the above specification and the components
          attached to these signals need to have a 3.3 V signaling tolerance."

    Therefore, I think the SK-AM69 incorrectly translates the SMBus voltage to +1.8V for the PCIe edge connector on page 37 of the schematics.

  • 0 in reply to John Eubanks
    TI__Guru 55005 points

    Thank your for the information.  Any additional questions for this E2E thread?