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Original question:

CC2651R3SIPA: CC2651R3SIPA

CC2651R3SIPA: Unused X32K_Q1/Q2 pins

Toshio Katsura
Prodigy 190 points
Part Number: CC2651R3SIPA
Other Parts Discussed in Thread: CC2652RSIP, CC2652PSIP, SYSCONFIG

Tool/software:

I'd like to make sure of "32.768-kHz crystal" pin in CC2651R3SIPA.
I'll NOT use "32.768-kHz crystal" pins, and will use external oscillator.

In "CC2651R3SIPA_datasheet_Rev.B" (cc2651r3sipa.pdf),
Table 7-2. Connections for Unused Pins – SIPA Package


X32K_Q1/Q2's unused PREFERRED PRACTICE is "NC" as follows.

Crystal Oscillator and Crystal Selection for the CC13xx, CC26xx, and CC23xx
Family of Wireless MCUs (SWRA495K.pdf)

Block diagram in "2.3 32.768-kHz Crystal Oscillator"

X32K_Q1 is connected to input pin of internal INV AMP.

"X32K_Q1" will be "NC, it's means input of INV AMP will be floating.
Will internal INV AMP oscillate?

And X32K_Q1's PREFERRED PRACTICE is "NC". is it correct?

Please let me know.

THKS.

  • 0
    TI__Mastermind 18655 points

    Hi,

    Please can you clarify:

    I'd like to make sure of "32.768-kHz crystal" pin in CC2651R3SIPA.
    I'll NOT use "32.768-kHz crystal" pins, and will use external oscillator.

    If I understand your question correctly, if using an external clock source (that is not a 32.768 kHz watch-type crystal), the clock 32.768 kHz signal should supplied using any digital IO pins as the clock input:

    • Section 9.12 of the CC2651R3SIPA datasheet
    • Section 1.3.7 of SWCU191 (CC13x1x3, CC26x1x3 SimpleLink Wireless MCU Technical Reference Manual): https://www.ti.com/lit/swcu191

    So, both X32K_Q1 and X32K_Q2 should then be NC.

    And X32K_Q1's PREFERRED PRACTICE is "NC". is it correct?

    Yes, NC is preferred.

    Regards,

    Zack

  • 0 in reply to ZC
    Prodigy 190 points

    Dear Zack,
    Thank you for your reply.

    > if using an external clock source (that is not a 32.768 kHz watch-type crystal),
    > the clock 32.768 kHz signal should supplied using any digital IO pins as the clock input:

    Yes, we will use digital IO pin (DIO11) as the clock input for oscillator:

    And we care followings.
    "X32K_Q1" will be "NC, it's means input of INV AMP will be floating.
    Will internal INV AMP oscillate?

    How about it.

    Thanks.

  • 0 in reply to Toshio Katsura
    TI__Genius 12960 points

    Hi Toshio,

    The CC2651R3SIPA module does not include a 32KHz XTAL within the module, however the device does have the internal 32KHz oscillator like our other ICs, but that would mean the slow clock accuracy would be +/-500 KHz as per our datasheet. Thus you can leaven this NC if using the internal oscillator. If you need more accuracy, they this would be where you connect the XTAL as we do in our reference designs. For example, the CC2652RSIP and CC2652PSIP include the XTAL within the module, so there is nothing to add, but for the CC2651RSIPA this is not the case.

    I hope this clarifies things.

    Thanks,

    Riz 

  • 0 in reply to Rizwan Murji
    Prodigy 190 points

    Dear Riz,

    Thank for your cooperation and reply examination.
    We'd like to use high clock accuracy with internal 32KHz oscillator and external 32KHz XTAL in CC2651RSIPA.
    So we select external 32KHz oscillator and input from DIO pin.

    We understand that when not using an external 32KHz XTAL, the X32K_Q1 pin, which is connected to the internal inverter amplifier, is recommended to be left as NC (No Connection).
    However, we are concerned that leaving the amplifier's input open might lead to oscillation. Could you please explain why it is acceptable to leave X32K_Q1 as NC in this scenario?

    Regards.

  • 0 in reply to Toshio Katsura
    TI__Genius 12960 points

    HI Toshio,

    You will use sysconfig to configure the source of the 32KHz  clock. Thus if you are using the internal slow clock, you will configure it as such, thus you can leave the pins as NC. No need for any additional termination. The configuration thru SW will take care of what is needed. 

    Thanks,

    Riz

  • 0 in reply to Rizwan Murji
    Prodigy 190 points

    Thank you for your reply,