DNMs on CC2650 Reference Schematic?

Ron Segal20

Other Parts Discussed in Thread: CC2650

Can somebody please clarify the significance of the DNM (Do no mount) components identified in the CC2650 reference design (CC2650EM-7ID_1)2_6_Schematic.pdf). In particular in I am unclear about the DNM capacitors for the main 24MHz crystal (C22 and C23), what value should these take (or not) and also C12, C2 and C10. How to handle all of these is not mentioned in the notes on the schematic. Any other observations for successfully making use of this design would also be appreciated. Best wishes, Ron

over 9 years ago

0 Igor Sherer over 9 years ago

Guru 31280 points

Hi Ron,

C22 and C23 are external load capacitors, however, the cc26xx family has internal load capacitors, therefore, the external one are not mandatory and can be used in cases where additional capacitance load is needed. You may add a footprint for capacitors, as mentioned on the reference schematic, but not to use it in the final PCB assembly.
Make sure you choose a 24 XTAl within the spec.

The following are used for tuning and matching:

C2 and C10 are an additional place for a large value decoupling capacitors, you may find it redundant in your final PCB version.
If I'm not mistaken, C12 is a footprint for additional BALUN matching component (in this case a capacitor). Where it be finally used, or not, is dictated by the mismatched impedance on the RF path between cc26xx device and the antenna/antenna connector.