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Original question:

CC2640 24MHz Crystal Load Caps setting on Eval Board

CC2642R: Default internal load capacitor,

paddu2017
Expert 2885 points

Part Number: CC2642R

Hi,

As per the "SWRA495F" and other E2E posts it is mentioned that "default setting of the internal capacitance is 9 pF",
but the Wiki(CC13xx CC26xx Crystal Tuning) mentions the internal capacitance is disabled by default.

#define SET_CCFG_MODE_CONF_XOSC_CAP_MOD 0x1 // Don't apply cap-array delta


Which is true? is the internal capacitance is disabled by default? or it is 9 pF?
I tried to execute CC2642R sample codes and it seems it is disabled in the source code(CCFG Registers).

Best Regards
paddu

  • 0
    TI__Mastermind 23730 points

    Hi paddu2017,

    Both are true. I think you are confused by what the cap-array delta does.

    The cap-array delta allows you to increase or decrease the internal capacitance based on some delta value (which is described in the Wiki). By default no delta is applied, and therefore the internal capacitance defaults to 9 pF.

    EDIT:

    As M-W pointed out, default internal capacitance is 9 pF for CC13x0/CC26x0 and 7 pF for CC13x2/CC26x2.

  • 0
    TI__Guru 58425 points
    Hi Paddu,

    I recommend you have a look at the new hardware design document:

    www.ti.com/.../swra640

    As for the default value, the cap tuning is disabled. When disabled, the cap value will be 9pF for CC13x0/CC26x0 or 7pF for CC13x2/CC26x2.
  • 0 in reply to IUsedToBeARealPerson (M-W)
    Expert 2885 points
    Hi Severin, M-W,

    Thank you very much for the quick reply.
    This cleared the confusion.

    One additional question on this.

    If the default internal cap is 7pF then we can choose not to use external 7pF Cap?
    Actually our custom board has external 7pF Cap, so in this case the internal Cap will also add up the total Cap will be 14pF?
    and in this case we should change the cap-array delta to "0" in CCFG?

    Best Regards
    paddu
  • 0 in reply to paddu2017
    TI__Mastermind 23730 points

    You can "disable" the internal cap-array by adjusting the cap-array to maximum negative delta which results in 0 pF. However, the measured capacitance over the internal cap-array includes an inherent parasitic capacitance of about 2 pF. This means "disabling" the internal cap-array yields 2 pF on both CC13x0/CC26x0 and CC13x2/CC26x2 devices.

    In order to set the internal cap-array to 0, set the following in your CCFG:

    // NOTE! This is specific for CC13x2/CC26x2 devices.
// Delta of -43 is the maximum delta for CC13x2/CC26x2 devices.
#define SET_CCFG_MODE_CONF_XOSC_CAP_MOD         0     // Apply cap-array delta
#define SET_CCFG_MODE_CONF_XOSC_CAPARRAY_DELTA  0xD5  // Equals delta -43

    Please refer to the conversion table found in the SWRA640 document:

    http://www.ti.com/lit/pdf/swra640