The question of not required for Fxx and later

[Tom.Fu]

Dear Support team

1) I find that there is a C9 in the nRF52840 reference circuitry for CKAA WLCSP which said that the C9 is not required for Fxx and later as the picture below.

2) We plan to use the chip nRF52840CKAA in the picture below for our project. Is there any problem if we place a 1nF capacitance at the position of C9?

[ketiljo]

The DEC5 is not connected internally on rev Fxx and later. So a cap here will just be a waisted component. 

[Tom.Fu]

Pardon, Is nRF52840CKAA the later one? Is  nRF52840CKAA allowed to connect a 1nF cap for the DEC5 or not to connect any cap?

[ketiljo]

The first part of the product code doesn't say what revision it is, please refer to this page: https://infocenter.nordicsemi.com/topic/comp_matrix_nrf52840/COMP/nrf52840/nRF52840_ic_revision_overview.html

Rev 3 doesn't need the cap at DEC5

[Tom.Fu]

Pardon， By the way, how to confirm the  nRF52840CKAA I use is belong to Rev 3? I find other Revs also have CKAA. 

[ketiljo]

You need to look at the complete part number, nRF52840CKAAXXX. There's no way to tell just with CKAA.