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CC1310: It is unclear what 32768 - crystal and load capacitors

Prodigy 50 points

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Part Number: CC1310

Hello.

In CC1310 datasheet (SWRS181C) on paragraph 5.19.3.2 noted that crystal load capacitance should be in range 6-12 pF. On the dev boards  CC1310EM-7XD-7793  and LAUNCHXL-CC1310 TI engineers used  crystal 32768Hz with CL=7pF (FC-135 32.7680KA-AG0) which corresponds to the datasheet. External crystal capacitors are 12pF, and from that we can make conclusion that TI took Cstray = 1 pF in their calculations.

However, on most of the TI dev boards  (TIDA-01519, TIDA-01476, TIDA-00488, TIDA-00489, TIDA-00646, TIDA-00838 ), used crystal FC-12M 32.7680KA-A3 with CL = 12.5pF, which slightly exceeds the datasheet MAX value of 12 pF

And more than that, on this boards external crystal capacitors are also 12pF, however this equation:

CL = (C1 * C2) / (C1 + C2) + Cstray

gives us C1, C2 = 22pF. 
This is pretty confusing.


Can anyone comment on this?

 

  • Dmitry,

    Thank you for bringing that to our attention, the TIDA's are wrong. The CC1310EM reference design is correct. I will ask the owners of the TIDA's to modify their designs.

    Regards,
    /TA

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