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CC2500: Crystal outputting DC

iFletch
Prodigy 220 points
Other Parts Discussed in Thread: MSP430F2471, CC2500, SIMPLICITI

I am working with a slight modification of the EZ430-rf2500 reference board, only change is switching the mcu to a msp430f2471. The msp side of the board programs and communicates fine, but the oscillator on the cc2500 is not starting (outputting ~1V DC). I did not change the connections on that side of the board, layout is identical to the reference board on that side. I tested with a second board and the crystal is outputting a bit less but oscillating at ~90MHz for a 26MHz crystal.

I think it is an issue with hardware, but I'm not sure what the issue could be. The connections look good and have continuity. Any ideas would be greatly appreciated. Thanks!

  • 0
    Mastermind 8170 points

    There is not enough information to make a good guess. Are you using "proven" code such as SimpiliTi or other tested code?  You write the layout is the same, are you using the same part types? numbers? If the  answer to these questions is yes I would look for assembly errors such as a incorrect part placement..

    If you are using a different xtal I would take a careful look at its data sheet for suggested loading cap values. Note that the pads on the board adds a little capcitance so the actual cap values will be a couple of pF less than the suggested value. The acutal value is layout dependent.  These caps should be NPO and +/- 10% or better. Generally if you are within +/- 20% of the correct value it will work, at least near room tempurature. The tighter the cap tolerance the more room for errors in the estimate. That is if the cap is +/- 20% then your estimate of the correct value must be spot on.

    Let me know how you make out.

    H

  • 0 in reply to H Stewart
    Prodigy 220 points

    Thank you for the reply.

    Whoops, forgot to mention I'm using SimpliciTI. The rest of the code (minus the chipcon piece) is verified and working, as are the signals going to the cc2500. Yes, I'm using the same part types and numbers. For the capacitors it's ceramic SMT in the same dimensions (from Digikey/Mouser). The board material might be a little thicker. I'll check out the capacitance values next, that's probably the issue.

  • 0 in reply to iFletch
    Prodigy 220 points

    Ended up being a bad lot of crystals. It's working fine now. Thanks again!

  • 0 in reply to iFletch
    Mastermind 8170 points

    We appreciate the feedback. Thanks