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LAUNCHXL-CC26X2R1: Effects of a bad 32 kHz crystal

kazola
Guru 18515 points
Part Number: LAUNCHXL-CC26X2R1

Tool/software:

Hi guys,

Due to some erroneous production step, some of our CC26X2R based boards feature an inaccurate crystal.

We measure them with the vanilla project zero code, where we add code to re-route the 32 kHz crystal to an output pin. We measure such output with a high-precision frequency counter.

For example, a bad value we see is 32772 Hz. The good value should obviously be 32768 Hz

I am not asking about how to solve this. Instead, I was wondering if someone could list the effects such oscillation offset can provoke.

For example, could this be the reason that a board with one of this "bad" oscillators takes more retries to connect (or it does not even connect) via Bluetooth?

Please, let us know.

Have a nice day.

  • +1
    TI__Expert 5830 points

    Hi Kazola,

    For sure an inaccurate crystal will affect the sleep time for the device and there's a limit to how inaccurate the clock can be. In the case of the Bluetooth LE specification there's a +/- 500 ppm limit. In your case, at least with the measurement done and the value provided you're not pushing that limit. It could be the case that over temperature or aging which will add to the frequency error and you could fall outside the limit. There's a little more background on that in this app note https://www.ti.com/lit/an/swra499c/swra499c.pdf which covers running the device without a 32kHz crystal and what the limitations and tradeoffs are for doing so in terms of power consumption.

    I'm not immediately thinking that this is the sole source of your problem though. Due to the problems in your production you might want to explore if it could be affecting other parts of the system like the 48MHz crystal which would also have an effect on the ability to connect since it's accuracy directly correlates to your TX/RX frequency.

    -Jake