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nRF52840 supply decoupling references

PC

The latest Objective Spec nRF52840 Objective Product Specification v0.5.1 got me a little confused since I was working off of v0.5 until few weeks ago. My application is a cross between Circuit Configuration #5 and #6 (pg 693-694), that is, no NFC/USB/EXTSUPPLY/DCDCEN0, but yes DCDCEN1.

  1. In v0.5.1, pin F23 got renamed from DEC6 (in v0.5 named DEC2).

What was the nature of this change? Was it just to discern between pin A18 which is also named DEC2, did the functionality change, etc?

  1. In v0.5.1, pin E24 DEC6 is tied to pin B5 DEC4 with a bypass cap C16 47nF.

What was the nature of these changes? I should follow v0.5.1 in my application? Is C16 more for DEC4 than DEC6, hence adding C16 instead of C10? I assume C16 is to additionally decouple higher frequencies C15 isn't - is that the intent?

The nRF52840 preview devkit (v0.9.x) doesn’t have this change found in v0.5.1. How would this change affect results seen with the devkit?

  1. There are 3 capacitors (C9, C10, C13) that are in layout but not mounted (N.C.). My application is very space constrained, and I’d like to not put these in the PCB layout if reasonable.

What are these for, and how much risk would it be to the intended performance of the SoC if not putting these provisions on my PCB? The datasheet describes as decoupling for radio/flash supply but I don’t see any examples of it caps being populated.

image description

Please advise.

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    Q1: It is a name change only, as you correctly pointed out it is to discern it from pin A18 which was also named DEC2.

    Q2: This change is due to the internal supply between DEC4 and DEC6 (DEC6 previously labelled DEC2 in v0.5.0) has been removed from the final product. The supply must now be connected externally for the final device layout. For the Prototype silicon currently sampling, this change can be made to development boards without changing device behavior. For the Final silicon, this change must be made or the device will not be functional.

    Q3: Since its an Objective Product Specification it means that . Thus I strongly recommend that you make room for the C9, C10 and C13 as these values may change. If these pins are labled as N.C in the final PS, i.e. v1.0, then the pins connected to the capacitors that are labeled N.C can simply be left floating.

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