CC26xx Tips and Tricks

From Texas Instruments Wiki
Jump to: navigation, search


How not to measure on the 24 MHz XTAL

If measuring on the 24 MHz XTAL oscillator pins, the device must be powered off, not running from the 24 MHz XOSC or not running on the DC/DC. The capacitance introduced by the measuring probe could affect the voltage regulator referencing the oscillator causing an overvoltage in the VDDR domain and damaging or even destroying the device. Ensure the power is down when measurements are to be done on the XTAL Oscillator.



How to adjust the 24 MHz load cap

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 9 pF setting according to the table below:

Delta Capacitance Delta Capacitance Delta Capacitance Delta Capacitance
-27 5 -17 6.2 -7 7.7 3 9.6
-26 5.1 -16 6.4 -6 7.7 4 9.8
-25 5.2 -15 6.5 -5 7.9 5 10.1
-24 5.3 -14 6.7 -4 8.2 6 10.3
-23 5.3 -13 6.8 -3 8.4 7 10.5
-22 5.5 -12 7 -2 8.6 8 10.7
-21 5.6 -11 7.1 -1 8.8 9 10.9
-20 5.8 -10 7.3 0 9 10 11.1
-19 5.9 -9 7.4 1 9.2
-18 6.1 -8 7.6 2 9.4