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CC3200: 40MHz crystal's load capacitance

Part Number: CC3200

Hi, in the CC3200 launchpad rev4.1's schematic, it uses the 6.2pF load capacitor.

As far as I know, in the Q24FA20H00396 's datasheet, the load capacitance is 8pF.

However, the launchpad schematic uses 6.2pF. Is there a reason? How is this load capacitance is calculated?

I couldn't find the data about the load capacitance in the CC3200's datasheet.

  • Hi David,

    The capacitance that we have on the launch pad is reduced due to the parasitics of the PCB board. So even though we have 6.2pF overall we will have a higher capacitance on the nodes.

    We provide a frequency tuning method for our devices. You can refer to:

    processors.wiki.ti.com/.../CC31xx_&_CC32xx_Frequency_Tuning for our tuning procedure on how to ensure you meet the +/-25PPM requirement over temperature and other variations.

    Thanks,
    Riz
  • Hi, Rizwan. In my case

    I'm going to follow the stack-up, provided from TI.

    0) So, you mean that the parasitic capacitance change when considering the PCB layers, thickness, trace width for load caps, etc?

    1) Also, if I stick to the stack-up and PCB trace from the launchpad rev4.1, the 6.2pF value won't change, does it?

    I use the CC3200R1M1RGCR chip.

  • Hi David,

    its based on the stack-up material and the routing of the XTAL to the CC3200 itself. Our recommendation would be to use the tuning procedure we provide on your first samples to determine your final capacitance values. If you keep the stack-up, routing and XTAL the same, you probably will be ok with what we use on the Launch pad.

    I hope this helps.

    Thanks,
    riz