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CC3100 - Is the 32.768 KHz crystal mandatory?

Enrico Migliore
Intellectual 690 points
Other Parts Discussed in Thread: CC3100, CC3100BOOST

Hi,

I'm interfacing the CC3100 transceiver to my products.

I'm reading the CC3100BOOST_SCH_REV3P3-A.pdf document which contain the schematics of the CC3100BOOST board.

I noticed that the schematics contains a 32.768 KHz crystal.

QUESTION 1:

Is that 32.768 KHz crystal mandatory for reliable operations?

QUESTION 2:

If I don't mount the 32.768 KHz crystal, will I be able to put into sleep mode the CC3100 transceiver?

Thanks,

Enrico Migliore

  • 0
    Guru 21435 points

    The following is from the datasheet - http://www.ti.com/product/CC3100/datasheet/specifications#swas0316447

    Clock Specifications

    The CC3100 device requires two separate clocks for its operation:

      • A slow clock running at 32.768 kHz is used for the RTC.
      • A fast clock running at 40 MHz is used by the device for the internal processor and the WLAN subsystem.

    The device features internal oscillators that enable the use of cheaper crystals rather than dedicated TCXOs for these clocks. The RTC can also be fed externally to provide reuse of an existing clock on the system and reduce overall cost.

    There are also details on using the Internal Oscillator for the Slow Clock.

    Glenn.

  • 0 in reply to Glenn Vassallo
    Intellectual 690 points

    Dear Glenn,

    thank you for your clear explanation.

    My question though is still unanswered.

    QUESTION 1:

    Can the CC3100 transceiver run without the 32.768 kHz external crystal?

    QUESTION 2:

    If yes, what kind of limitations will the CC3100 transceiver face?

    Thanks,

    Enrico Migliore

  • 0 in reply to Enrico Migliore
    Guru 21435 points

    If I understand your original question correctly. You want to not include an RTC but still wish to support hibernation. If so, then this is not covered in the data sheet as hibernation assumes the presence of the RTC. As such, i'll need leave your questions to be covered by  someone who can provide you a definitive answer. 

    Glenn.

  • 0 in reply to Glenn Vassallo
    TI__Expert 4345 points

    All,

    The feature to allow operation without a 32kHz crystal is not verified today and therefore is not recommended.

    However, we are look into enabling this feature in the future. Note, however, that 32 KHz clock is always required for applications using infrastructure power save mode.

    Adnan

  • 0 in reply to Adnan
    Intellectual 690 points

    Dear Adnan,

    that's the answer I wanted. Thank you.

    Enrico Migliore