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Hi Team, 

Need one confirmation for AD7949, is the exposed pad MUST be soldered? Customer would like to skip this soldering during prototype, is it ok?


Refer to page 9

21 (EPAD) Exposed Pad (EPAD) NC The exposed pad is not connected internally. For increased reliability of the solder joints, it is recommended that the pad be soldered to the system ground plane




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[edited by: @skowalik at 3:51 PM (GMT 0) on 21 Nov 2019]
  • John,

    For prototyping you are probably okay not soldering the exposed paddle.  Just be sure that per the recommendation any exposed metal below the package is tied to ground in case something conductive happens to find its way between the paddle and the PCB.  

    For production I would ensure it is soldered to avoid violating any of the abs max ratings.


  • Customer has following question on AD7949.

     1) The MCU that I use only can output either 8-bit or 16-bit data format for SPI.

         Meaning that there will be 16 SCK pulses.

         The AD7949 required only 14 SCK pulses.

         Will there be any issue with the additional 2 SCK pulses?

         How is the data (CFG register and DATA) being interpreted with this 16 SCK pulses?


    2) If the above has no issue, will it be okay if the 16 SCK pulses is not continuous, meaning there is a time gap (5us) between pulse 8 & 9?

  • John,

    1) This is not a problem as SDO will simply go to a high impedance state after the 15th falling edge.

    2) This too should not be an issue.   This operation would be essentially like a read-span-convert operation, whereby the user executes the first 8 bit transfer, initiates a new conversion and then reads the last 8 bits while the next conversion is in process.


  • @skowalik Thanks for the support. 

    Good news. Customer will select ADI solution, i.e.

    1) AD7949

    2) AD8221

    3) DAC5621

    Customer have some question on PCB setup. 

    1) I am using 4 layer PCB. Inner layer 1 will be a ground plane. 

        In this case, should I split the ground plane into digital and analog ground plane?

        If I split the ground, how and where should I join both digital and analog ground?

        It always says join both ground plane at one point only, meaning I shouldn't join them in multiple points?

    2) For the grounding of decoupling capacitor, should it be connected to digital ground or analog ground?

     Do you able to support these?