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CC13xx CC26xx Crystal Tuning

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How to measure the 24/48 MHz* crystal frequency

As noted in the device datasheets, oscillator probes must not be applied directly on the crystal pad while the device is running as this can physically damage the built-in DCDC regulator.

One way to mitigate this is to disable the DCDC regulator before doing the measurement. The best way to measure the frequency though is to make the radio output an RF carrier and measure the frequency (offset) using a spectrum analyzer.

  • CC13x0/CC26x0 devices only support 24 MHz crystals while CC13x2/CC26x2 devices only support 48 MHz crystals.



How to adjust the internal load capacitor array

The internal crystal load capacitance is changed by editing the following lines in ccfg.c:

//**************************************************
// Enable XOSC cap-array delta
//**************************************************
// #define SET_CCFG_MODE_CONF_XOSC_CAP_MOD              0x0        // Apply cap-array delta 
#define SET_CCFG_MODE_CONF_XOSC_CAP_MOD                 0x1        // Don't apply cap-array delta 

Change to apply cap-array delta.

//**************************************************
// Value of XOSC cap-array delta
//**************************************************
#define SET_CCFG_MODE_CONF_XOSC_CAPARRAY_DELTA          0xFF       // Signed 8-bit value, directly modifying trimmed XOSC cap-array value

The delta value is capacitance offset from the default setting according to the table below:

Capacitance measured on
TI EVM (including parasitics)
CCFG Delta value for
CC13x0/CC26x0 QFN
CCFG Delta value for
CC13x0/CC26x0 WCSP
CCFG Delta value for
CC13x2/CC26x2 QFN
2,0 -57 -30 -43
2,1 -56 -29 -42
2,2 -55 -28 -41
2,3 -54 -27 -40
2,4 -53 -26 -39
2,5 -52 -25 -38
2,6 -51 -24 -37
2,7 -50 -23 -36
2,7 -49 -22 -35
2,8 -48 -21 -34
2,9 -47 -20 -33
3,0 -46 -19 -32
3,1 -45 -18 -31
3,2 -44 -17 -30
3,3 -43 -16 -29
3,4 -42 -15 -28
3,4 -41 -14 -27
3,4 -40 -13 -26
3,6 -39 -12 -25
3,7 -38 -11 -24
3,8 -37 -10 -23
3,9 -36 -9 -22
4,0 -35 -8 -21
4,1 -34 -7 -20
4,3 -33 -6 -19
4,4 -32 -5 -18
4,5 -31 -4 -17
4,6 -30 -3 -16
4,7 -29 -2 -15
4,8 -28 -1 -14
5,0 -27 0 -13
5,1 -26 1 -12
5,2 -25 2 -11
5,3 -24 3 -10
5,3 -23 4 -9
5,5 -22 5 -8
5,6 -21 6 -7
5,8 -20 7 -6
5,9 -19 8 -5
6,1 -18 9 -4
6,2 -17 10 -3
6,4 -16 11 -2
6,5 -15 12 -1
6,7 -14 13 0
6,8 -13 14 1
7,0 -12 15 2
7,1 -11 16 3
7,3 -10 17 4
7,4 -9 18 5
7,6 -8 19 6
7,7 -7 20 7
7,7 -6 21 8
7,9 -5 22 9
8,2 -4 23 10
8,4 -3 24 11
8,6 -2 25 12
8,8 -1 26 13
9,0 0 27 14
9,2 1 28 15
9,4 2 29 16
9,6 3 30 17
9,8 4 31 18
10,1 5 32 19
10,3 6 33 20
10,5 7 34 21
10,7 8 35 22
10,9 9 36 23
11,1 10 37 24