ADM1278_Placement_FET and Rsense

Dear Sir/Madam,

We are using ADM1278 in our Server design for hot-swapping. it's used to 2 PSU so We will be going to share FET and R sense for placement. 5 FETs on the left near PSU1 and 4 FETs on the right near PSU0. Is this right ?. Please let me know your guidance. 

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  • 0
    •  Analog Employees 
    on Jun 4, 2021 4:40 PM

    Hi Toan,

        If you have not already done so, I recommend using the spreadsheet design tool on the ADI ADM1278 web page. This will assure reasonable design constraints at the schematic level.

    www.analog.com/.../ADM1278_Design_Spreadsheet_Tool.zip

        Your layout is a little bit difficult to see at this resolution. It looks very compact, which is both bad and good. You want to be careful to remove the heat from the FETs, and a compact layout can make that more difficult. More copper drain area is recommended by the FET vendor. Also ensure sufficient airflow to carry away the heat.

        The red polygons represent VIN, correct? I recommend that you space out the sense resistors between the FETs and make the metal as symmetrical as possible so current sharing and heat distribution is as even as possible. The red polygon on the right looks non-symmetrical, which will reduce even current sharing.

        It is good that the ADM1278 controller is located close to its FETs. Make sure to route SENSE+ and SENSE- as a differential pair away from noisy signals, and with a nearby ground plane for shielding, if possible. Also, route GATE at 3x minimum width to carry 1.5A during rapid shutdown events.

        The ADM1278 has two separate ground pins. AGND and all of the analog components associated with the IC should be connected to a small AGND island around the IC. Connect AGND to the main ground plane of the board at a single point to make sure AGND is quiet and any ground plane noise is common mode to the IC. Connect the other GND pin to the board GND plane.

    Thanks!

      Nathan

  • Thanks Nathan.

    I got it but I still confuse about thermal and EMI/EMC and anything issue.

    we are 2 options:

    ADM1278 located close to 9 FETs. so the  hot-swapping functions placed at one side near PSU0 or PSU1

    + ADM1278 controller only located close to  4 FETs on the right of the board that closes to PSU1 and so far 4 FETs on the left of the board closes to PSU0 connector. We are using 9 FETs. 

     Do you have a comment for their cases?.

    PLease let us know the best case?

      

Reply
  • Thanks Nathan.

    I got it but I still confuse about thermal and EMI/EMC and anything issue.

    we are 2 options:

    ADM1278 located close to 9 FETs. so the  hot-swapping functions placed at one side near PSU0 or PSU1

    + ADM1278 controller only located close to  4 FETs on the right of the board that closes to PSU1 and so far 4 FETs on the left of the board closes to PSU0 connector. We are using 9 FETs. 

     Do you have a comment for their cases?.

    PLease let us know the best case?

      

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