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CC2591 Layout question

Yuval Klein
Expert 1100 points

Other Parts Discussed in Thread: CC2591, CC2530

Hi,

I am designing a Zigbee coordinator using CC2530 and CC2591. I really need to separate the digital ground of the circuit from earth ground (chassis) but I do not understand how to deal with the RF antenna. I intend to use an SMA connector mounted on my metal enclosure which create a short between the two different ground plains.

Thanks,

Yuval

  • 0
    TI__Mastermind 36415 points

    Yuval, 

    Honestly the best you can do with mixed signals devices like a CC2530 is to have one single ground plane and make the ground as good as possible.

    And when I say good, the measure is how close can you get it to the device (if you are using 4 layer board, then have layer 2 become GND) and the next item is to have as few holes and cutouts in the ground plane as possible and nothing under the RF, XTAL and ADC sections.

    In any case we would be happy to help you review your layouts.

    Regards,
    /TA 

  • 0 in reply to TA12012
    Expert 1100 points

    Hi,

    Thanks for the fast reply. My fear from having one ground plane is the noise I'll get from the reset of the circuit (I have micro-controller, DC/DC, Ethernet PHY and USB bridge). Another problem is that the antenna connector will be mounted to metallic box (my chassis ground) and not I'll have a short between the chassis and the only ground in the circuit.

    Please advice.

    Regards,

    Yuval

  • 0 in reply to Yuval Klein
    Guru 31280 points

    Hi Yuval,

    The chassis ground is not the same ground of the PCB with ZigBee devices??

  • 0 in reply to Igor Sherer
    Expert 1100 points

    Hi Igor,

    I don't see any way around it. I'm trying to avoid it since the RF ground needs to be connected to the digital ground and now they are all connected to the chassis ground and I'm afraid from noise to leak anywhere.

    Any idea how to menage the grounds?

    Yuval

  • 0 in reply to Yuval Klein
    Guru 31280 points

    Well, I'm not familiar with you system, but the SMA connector must be attached to the chassis?
    Is it one of the holding points?

  • 0 in reply to Igor Sherer
    Expert 1100 points

    Well, I'm looking for an isolated SMA connector but for now it's connected to the chassis. It's not an holding point.

  • 0 in reply to Yuval Klein
    Guru 31280 points

    Hi Yuval,

    Well, I have an idea, though it's a bit clumsy.

    You can use a long type of SMA connector, while partially cover it with

    a shrinking insulator (Hebrew: בידוד מתכווץ). So the place where this SMA

    connector is is in touch with the chassis insulated while you still have enough

    length to connect the antenna.