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Issue with Balun selection for CC2650

Other Parts Discussed in Thread: CC2650, CC2640

Hi There 

Since LFB182G45BG5D920 from Murata ( the only balun used in CC2650 reference designs) is not released yet, could anyone  tell me how to choose the alternatives? 

Since the CC2650's Optimum load impedance is not measured by TI yet, what impedance value you (TI Engineers) use to choose LFB182G45BG5D920 as the conjugate impedance matching ?

Please give out the load impedance range ( not have to be the optimum one) for CC2650, so it is easier for us to find any Balun that may already in the market. 

Thanks

Best

Fu

  • Hi Fu,

    Please follow the reference designs for discrete component matching. You won't currently find any other integrated baluns in the market that matches the CC26xx.
    The LFB182G45BG5D920 was not selected for CC26xx, it was designed specifically for it.

    In the other thread there is contact information for a Murata representative that can help you out with samples.

    Cheers,
    Fredrik
  • Hi Fredrik

    Thank you very much for your answer.

    I already contact Murata representative for samples and waiting for the response.

    In the mean time, I have two more questions that need your help. 

    1. If I use LFB182G45BG5D920 as balun, can I connect this balun with 2450AT42A100E (2.4GHz chip antenna from Johanson Technology) ?

    2. Should I also do the impedance control on the traces that go from CC26xx (the MCU) to LFB182G45BG5D920 (the Balun) ?

    I do appreciate your suggestions and advice. 

    Thank you. 

    Best regards

    Fu

  • Hi Fu,

    1. Yes
    2. These traces should be as short as possible. No specific impedance control is required due to the short length

    Cheers,
    Fredrik
  • Hi Fredrik

    Thank you for your answer. That helps a lot !

    Best

    Fu

  • Hi Fredrik 

    I have two more questions regarding to CC2650 design. 

    1. The trace length from CC2650 to Balun ( LFB182G45BG5D920 ) is 3mm in my design. Is this short enough ?

    2. What pins are needed to be able to program CC2650 ?

        The pins are available in my design are: 

        JTAG_TCKC

        JTAG_TMSC

        NRESET

        DIO_2, 5, 6, 13, 14.

        VCC

        GND

        I am looking forward to hearing from you. 

        Thanks a lot

        Best regards

        Fu 

  • Hi Fredrik ,

    We are using the LFB182G45BG5D920 balun and chip antenna by Johanson i.e, 2450AT42A100E. What impedance matching circuit should be used? What should be the values of the components that we will be using? Is there any reference diagram having both the components? Kindle let me know regarding the same.

    Regards,
    Digvijay.
  • Hi,
    For the balun, you do not need matching. For the antenna, you will most likely need matching. Comp values etc will depend of the size of PCB, batteries, casing etc. We recommend adding at least a series and a shunt comp before the antenna, I am sure that the antenna vendor can give you more specific advice. You can also see some general guidelines in our antenna selection guide AN058 www.ti.com/.../swra161b.pdf
  • Hi Charlotte,

    Thanks for your immediate reply. So before the antenna do we have to use the RC circuit or the LC circuit? Because on net when I searched I have found the following:

    One reference diagram that I got is from TI:
    www.ti.com/.../getliterature.tsp

    Another is: upverter.com/.../

    Kindly let me know among the two which one I need to Follow?

    Regards,
    Digvijay
  • This really depend on the design it self. If you go through our ref designs, you will see that for the same antenna, we can use different antenna matching circuits depending on the design. The app note I referred to will explain this. If you have space on your board, a pi network (shunt, series, shunt) gives you the best matching options, but if the space is limited, I would go for the series and shunt option. The antenna vendor knows the antenna best and might be able to give more specific guidelines.
  • Thanks charlotte for your reply. Since I am short of space I'l go for series and shunt option of LC circuit.

    Regards,
    Digvijay
  • So Charlotte instead of Resistor - capacitor circuit you will recommend for Inductor- Capacitor Circuit for matching?

    Digvijay
  • Digvijay,

    You do not know what type of components or what values you need before you have built your first prototypes. Then you measure the antenna impedance with a network analyzer to determine the correct matching.

    Before that, you do not apply any matching and simply use 0-ohm resistors for the series component and do not mount the shunts.

    Cheers,
    Fredrik
  • Hi Fu Luo,

    I'm working on a design using CC2640 for BLE communication. I'm facing a similar problem as you mentioned of Balun selection. 

    Though I have found the optimum load impedance for TI CC26xx (http://processors.wiki.ti.com/index.php/CC26xx_Optimal_Load_Impedance)

    I'm planning to use CC2450AT07A0100 from johanson technology for antenna. I am not an expert in RF, so can you point me to the calculations/method or some link on how to select a balun based on optimum load impedance. I've been already reading about it but haven't found something tangible yet.

    Thanks in advance.

  • Hi Anurag,

    You should follow the reference designs for balun schematic and layout. 

    Cheers,

    Fredrik