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CC3235MODASF: RF Layout Recommendations

Ryan Walker
Prodigy 65 points
Part Number: CC3235MODASF


Hello,

I can't seem to find a good description of the recommended layout for the CC3235MODASF. The datasheet includes a section called "10.3.3 CC3235MODAx RF Layout Recommendations", but the information is very limited and I believe it may be incorrect. It shows a 6mm ground clearance from the edge of the module, but this would not fully provide ground clearance under the antenna region (there is 1mm not cleared). I think the 6mm measurement should actually be from the edge of the PCB (not the module). Please see the attached image that illustrates this better.

Also, in the section "10.3.2 CC3235MODx RF Layout Recommendations" for the module without the onboard antenna, it recommends a copper clearance on the top layer under the RF-BG pin. It doesn't recommend this for the CC3235MODASF, but in a separate reference document for the (non-existent?) CC3235MODASF Launchpad layout, this clearance is included. The 6mm antenna clearance also appears to be inline with the correction I mentioned above. Again, please see the attached picture for more details.

Can you provide a better reference layout for this module with more accurate dimensions? Even if the existing drawing is correct, the dimensions reference the module edge which has a +-0.25mm tolerance, which is not ideal for an RF reference. 

Thanks,

Ryan

  • 0
    TI__Prodigy 540 points

    Hi Ryan,

    The recommendations under "10.3.3 CC3235MODAx RF Layout Recommendations" should be correct for the antenna layout. The antenna has been thoroughly tested at our internal labs, and the documentation for this should reflect the findings for best performance. This means the 1mm of the antenna that is not cleared is on purpose. 

    We will not provide a different reference layout as we are confident in the design and previous customers have leveraged these files before. 

    As for your second part of your post concerning the 10.3.2 section, I would not refer to the CC3235MODASF launchpad layout as it seems that the hardware doesn't seem to be on ti.com. It is possible the files aren't updated/developed to match the good specifications provided by the CC3235MODASF reference design. 

    All that being said, if you believe that the RF reference design isn't ideal, you are welcome to implement the needed changes into your design. However, we cannot guarantee the same performance listed on our documentation/datasheets.  

  • 0 in reply to Andy Bui
    Prodigy 65 points

    Hi Andy,

    Is there any other documentation that confirms this? The RF layout is an important aspect of this design and typically includes more details about the layout. If testing was done, is there documentation to support this and the design used during test?

    The CC3235MODASF launchpad (that doesn't technically exist) appears to the board pictured in "10.3.3 CC3235MODAx RF Layout Recommendations", and the dimensions listed do not match.

    Thanks,
    Ryan

  • 0 in reply to Ryan Walker
    TI__Prodigy 540 points

    Hi Ryan,

    The figure in 10.3.3 should only be used for reference for placing the module/the PCB antenna. As listed in 10.3.3, the figure has the antenna with an overhang of 1mm off the PCB and a 6mm ground clearance on both sides. What dimension is not matching here? 

  • 0 in reply to Andy Bui
    Prodigy 65 points

    Hi Andy,

    The distance of the ground clearance from the edge of the PCB does not match. As pictured in the datasheet, it shows the clearance to be 6mm from the edge of the module. This would put it 5mm from the edge of the board. In the layout for the launchpad (that is pictured, and I'm guessing was used during testing), the ground clearance is 6mm from the edge of the board.

    Placing the clearance 6mm from the edge of the board seems more correct, as it it does not cover any of the antenna region. But this is not what is shown in the datasheet.

    Could you please escalate this or put us in contact with one of your RF engineers? We are planning to make a significant investment in this product and would like a definitive answer as this will have a significant impact on our products' performance.

    Thanks,
    Ryan

  • 0 in reply to Ryan Walker
    TI__Prodigy 540 points

    Hi Ryan,

    Let me check with another apps engineer on this. I'll get back to you tomorrow. 

  • 0 in reply to Andy Bui
    TI__Prodigy 540 points

    Hi Ryan,

    I checked in with one of our experts on this. We've verified that the CC3235MODASF launch pad reference design file (swrr169.zip) is valid and up to date on the guidelines. You can refer to this on the cutout for the RF pad. You can also refer to the CAD/Gerber files within the zip to check the dimensions for the PCB and copper clearance. Using this, it is confirmed that the distance between the copper clearance and edge of the PCB is 6mm. There is a 1mm overhang of the antenna, totaling for a total antenna length of 7mm. This means the data sheet image reference for antenna placement is incorrect - the dotted line for the 6mm (farthest left measurement) should end at the edge of the board, not the top of the antenna. Thanks for pointing this out to us, we will record this down so we can correct this error in a future revision. All the other/additional guidelines should be followed. As for documentation for documentation on supporting the antenna placement - the best document I can provide is our certification reports which can be found here. Hundreds of customers have leveraged this certification before which reinforces the guidelines provided in our datasheet.

    Let me know if there's anything else I can help with / clarify.