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CC430F6137 problem with crystal selection

Christine
Prodigy 100 points
Other Parts Discussed in Thread: CC430F6137

I am working with CC430F6137. I have successfully selected a 26Mhz crystal (2 pins,DIP ) to complete the wireless communication.

This time I want to minimize the size of the PCB board and select a crystal with the same capability(±20ppm) (4pins, SMD). However, the communication is not successful now. The circuit board is exactly same with that before.  2 diagnal pins of the crystal are connected to GND, and the other two are connected with RF_XINT and RF_XOUT.

Should I change the capacitance(C21 , C22) or it there anthing wrong?

Can anyone help me ?

Thank you!

  • 0
    Guru 227245 points

    Crystals are jsut a capacitive/inductive part inside an oscillator loop. IIRC, the MSP uses a Pierce oscillator. In this circuit, the crystal requires a capacitive load to GND, so the oscillator can oscillate with the crystal as the frequency-controlling part. But idfferent crystals require different load capacitance. Most likely you'll have to change C21 and C22 to meet the new crystals requirements. See the crystal datasheet for required load capacitane. For a require dload of x, the two capacitors need to be (2x-1). (the -1 is for the MSP pin capacitance. Any further parasitic capacitance due to PCB traces needs to be subtracted too)

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