SWRA495L December   2015  – April 2025 CC1310 , CC1350 , CC2620 , CC2630 , CC2640 , CC2640R2F , CC2640R2F-Q1 , CC2642R-Q1 , CC2650 , CC2662R-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Oscillator and Crystal Basics
    1. 1.1 Oscillator Operation
    2. 1.2 Quartz Crystal Electrical Model
      1. 1.2.1 Frequency of Oscillation
      2. 1.2.2 Equivalent Series Resistance
      3. 1.2.3 Drive Level
      4. 1.2.4 Crystal Pulling
    3. 1.3 Negative Resistance
    4. 1.4 Time Constant of the Oscillator
  5. 2 Overview of Crystal Oscillators for CC devices
    1. 2.1 24MHz and 48MHz Crystal Oscillator
    2. 2.2 24MHz and 48MHz Crystal Control Loop
    3. 2.3 32.768kHz Crystal Oscillator
  6. 3 Selecting Crystals for the CC devices
    1. 3.1 Mode of Operation
    2. 3.2 Frequency Accuracy
      1. 3.2.1 24MHz and 48MHz Crystal
      2. 3.2.2 32.768kHz Crystal
    3. 3.3 Load Capacitance
    4. 3.4 ESR and Start-Up Time
    5. 3.5 Drive Level and Power Consumption
    6. 3.6 Crystal Package Size
  7. 4 PCB Layout of the Crystal
  8. 5 Measuring the Amplitude of the Oscillations of Your Crystal
    1. 5.1 Measuring Start-Up Time to Determine HPMRAMP1_TH and XOSC_HF_FAST_START
  9. 6 Crystals for CC13xx, CC26xx, CC23xx and CC27xx
  10. 7 High Performance BAW Oscillator
  11. 8 CC23XX and CC27XX Software Amplitude Compensation
  12. 9 Internal Capacitor Array for CC23XX and CC27XX
  13. 10Internal Capacitor Array for CC13xx and CC26xx
  14. 11Summary
  15. 12References
  16. 13Revision History

9 Internal Capacitor Array for CC23XX and CC27XX

Overview

The 48MHz HFXT (High-Frequency Crystal Oscillator) Capacitor Array is designed to fine-tune the frequency of the crystal by adjusting the load capacitance. This section provides an overview of the configuration, key considerations, and best practices.

The capacitor array is organized as 16 capacitors in series across 4 rows per pin, allowing for precise tuning of the load capacitance.

Internal Capacitor Array DiagramFigure 9-1 Internal Capacitor Array Diagram

Programming the Capacitor Array

The capacitor array is configurable through the syscfg file in the SDK under Device Configuration.

  • Trim codes range from 0 to 63 (0x0 to 0x3F) per pin.
Note: Avoid using trim codes 16 and 48 to prevent a non-monotonic trim curve.

Load Capacitance Considerations

The total load capacitance affecting the crystal frequency consists of:

  • Pin capacitance (≃7pF per pin)
  • Capacitor array contribution (Q1CAP + Q2CAP, up to 13pF each)
  • Additional contributions from PCB layout and package characteristics

Limitations

  • Users cannot disable the capacitor array feature.
  • If external load capacitors are used, then TI recommends to set Q1CAP and Q2CAP to 0 in the syscfg file. This results in an estimated total parasitic capacitance of approximately 3-4pF.
  • There is a slight temperature dependence which can be more evident in temperature values above 105℃. This can be mitigated by accounting for the frequency shift since the effect is greatly predictable with structured behavior that is easily observable.

Internal Capacitor Array Values for CC23XX and CC27XX

Cap Array Value (Q1 = Q2)

Measured Capacitance on Reference Board for CC23xx (pF)Measured Capacitance on Reference Board for CC27xx (pF)

1

3.7

3.9

2

3.7

4.0

3

3.8

4.1

4

3.9

4.1

5

4.0

4.2

6

4.1

4.3

7

4.1

4.4

8

4.2

4.4

9

4.3

4.5

10

4.4

4.6

11

4.4

4.7

12

4.5

4.7

13

4.6

4.8

14

4.6

4.9

15

4.7

5.0

16

4.7

5.0

17

4.8

5.0

18

4.9

5.1

19

5.0

5.2

20

5.1

5.3

21

5.2

5.4

22

5.3

5.5

23

5.3

5.6

24

5.4

5.7

25

5.5

5.8

26

5.6

5.9

27

5.7

6.0

28

5.8

6.1

29

5.9

6.2

30

6.0

6.3

31

6.1

6.4

32

6.3

6.6

33

6.4

6.7

34

6.5

6.8

35

6.6

6.9

36

6.7

7.0

37

6.8

7.2

38

6.9

7.3

39

7.1

7.4

40

7.2

7.5

41

7.3

7.6

42

7.4

7.8

43

7.5

7.9

44

7.6

8.0

45

7.7

8.1

46

7.8

8.2

47

7.9

8.3

48

7.9

8.3

49

8.1

8.5

50

8.3

8.7

51

8.4

8.8

52

8.6

9.0

53

8.7

9.2

54

8.9

9.3

55

9.0

9.5

56

9.2

9.7

57

9.3

9.8

58

9.5

10.0

59

9.6

10.1

60

9.8

10.3

61

9.9

10.5

For further details on tuning the crystal, please contact technical support.