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MSP-EXP430FR5994: High Frequency Crystal Selection

Matthew MUSKOVAC
Prodigy 80 points
Part Number: MSP-EXP430FR5994


I want to add a high-frequency crystal to my MSP-EXP430FR5994 development board. I believe that it should be a type HC49. This is the part that I want to use https://www.foxonline.com/wp-content/uploads/pdfs/C4ST.pdf , will this part work? For an 8 MHz crystal, what value cap should I use for C8 and C9? 

  • 0
    TI__Expert 4695 points

    The crystal requirements are documented in the datasheet starting from page 38

    Lukas

  • 0
    TI__Guru 71216 points

    Hello Matthew,

    Typically the required values is determined in the crystal manufacturers datasheet (refer to the second sheet of the manufacturer's datasheet you provided for example).

    The specified load capacitance value shown is the combined capacitance for the load caps, pin capacitance and any stray capacitance.

    The following comes from SNLA290, a guide for crystal selection.

  • 0 in reply to Dennis Lehman
    Prodigy 80 points

    Thanks.

    The crystal that I chose has a Cload of 20 pF. Assuming Cpin and Cstray are the same as your example, I get CL1 = CL2 = 2*(20-1-3) = 34 pF. I ordered 33 pF.

    Since this is a DEVELOPMENT board, the user's manual should be more friendly. 

    1. The capacitor physical type should be specified for the HFX crystal. I believe it should be an HC49.

    2. Cstray should be specified, this is a TI board, you should know it, I can only guess.

    3. The physical size of the capacitor should be specified. Based on my measurements of the pads, I believe that 0402 will work, that is what I ordered.

    I love these development boards. I am an EE, I can figure this out (with a little help in this case). If I was a non-EE hobbyist, I may have thrown all the TI stuff away in frustration and bought an Arduino. Maybe TI doesn't care about the hobbyist market (?).

  • 0 in reply to Matthew MUSKOVAC
    TI__Guru 71216 points

    Matthew,

    Lukas makes a very good point with regard to crystal requirements in the datasheet.  You will have to take into consideration the additional loading presented by the oscillator.

  • 0 in reply to Dennis Lehman
    TI__Guru 71216 points

    Hi Matthew,

    With regards to the crystal and cap footprints, yes, the caps are 0402 according to the design files that are posted on the web.  Also, the BOM shows the crystal foot print to accommodate several sizes.

  • 0 in reply to Dennis Lehman
    Prodigy 80 points

    I wanted to get this working before I considered it to be resolved.

    I ordered a Fox Electronics FC4STCBMF8.0-BAG200 and 33 pF 0402 caps. I soldered them to the dev board. I wrote a simple program that uses the HFTX source for Timer A. It is working. Thanks.

    The documentation could be more friendly. Instead of just saying "different crystal types" it should list the types that will work (or recommended).

    I can't find where the cap size is listed. Maybe it is in the Eagle files. It should be in the User's Guide.

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