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      Molex Mini-Fit Jr – Know your Power, and Don’t Get Confused – “PCIe” and “Xilinx Not PCIe” Power Connector

      PCI Express Connectivity, , , , , , ,

      Our Mission: If It Is Packets, We Make It Go Faster – today more on PCIe, this time, Powering PCIe Cards with FPGAs…

      And with packets we mean: Networking using TCP/UDP/IP over 10G/25G/50G/100G Ethernet; PCI Express (PCIe), CXL, OpenCAPI; data storage using SATA, SAS, USB, NVMe; video image processing using HDMI, DisplayPort, SDI, FPD-III.

      To move packets you need power, but how much can you draw from an interface?

      PCI Express Cards Consumption Limit

      PCIe has been around for a long time, since 2003, and many people know the maximum power draw of 75W per PCIe slot, but is it that simple? The short answer is no, but let’s have a look into the spec. It states that all cards can consume up to 3A on the 3.3 V power rail with the following restrictions applying:

      • x1 cards: 0,5A on 12V, but overall consumption limit is 10W
      • x4 – x16 cards: 2,1A on 12V, but overall consumption limit is 25W 

      But where does the 75W come from? Well, exceptions apply:

      High power devices can draw more power after the initialization and configuration:

      • x1 cards can consume 25W 
      • x16 cards can consume 75W

      Using Additional Connectors for Higher PCIe Card Consumption

      With additional connectors (6pin and 8 pin) cards can consume up to 300W. A 6 pin adds 75W while a 8 pin adds 150W.

      But be careful, in the FPGA world there are two versions of the 6/8 pin Molex Mini-Fit Jr connectors, the Xilinx and the PCIe option. 

      The 6 Pin option has 2 pins (3 and 4) swapped. If you mix up the connectors 12V will directly connect to Ground, this can destroy your device.

      6 Pin Power Connector
      Pin PCIe Spec AMD/Xilinx Dev Boards
      1 +12 V +12 V
      2 +12 V +12 V
      3 +12 V Ground
      4 Ground +12 V
      5 Sense Sense
      6 Ground Ground

      The 8 Pin option the changes are less subtle, all pins have a different function and cause an electrical short.

      8 Pin Power Connector
      Pin PCIe Spec AMD/Xilinx Alveo Cards
      1 +12 V Ground
      2 +12 V Ground
      3 +12 V Ground
      4 Sense1 Ground
      5 Ground +12 V
      6 Sense0 +12 V
      7 Ground +12 V
      8 Ground +12 V