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Original question:

CC2340R5: CC2340R5: How to modify the matching capacitance of the crystal using studio8

CC2340R5: HFXT External Capacitor Value

David Linkh
Intellectual 885 points
Part Number: CC2340R5

Tool/software:

Hi BLE team,

I am using RF Studio 8, and want to use an external crystal with a load capacitance of 8pF. What would be the specific values I put into the Q1 and Q2 sections of the HFXT cap-array tuning? Would it be 8 for both Q1 and Q2, or a different value?

Sincerely,

David

  • +1
    TI__Expert 6520 points

    Hi David,

    The cap array setting in SmartRF Studio is a register setting and doesn't translate to the actual capacitance value being applied. For example a setting of 8 doesn't mean 8pF. For an 8pF crystal you need to have the total load be 8pF (including any parasitics). The easiest way to get the most precise setting is to run a series of experiments. You can set the system to output a CW at a specific frequency and measure the frequency with your spectrum analyzer. Any offset in the crystal frequency due to incorrect load capacitance will be seen as an offset in the CW frequency. You can then adjust the values for Q1 and Q2 until the error is minimized. This will give you the optimum value for your system including any parasitics.

    -Jake