RE: Custom PCB with the NRF52840: Programming, Antenna, USB, and Crystal

ryerye120 — Tue, 28 Jul 2020 17:12:19 GMT

Sorry for the late reply - I forgot to say thank you because your message was such a relief. Thank you!

I just have a clarifying question: I assume this is the J-link debugger port on the dev kit:

I will submit another ticket with my schematic and layout to get a quick review from you guys! That'd be amazing.

Thanks for all your help,

Ryan

RE: Custom PCB with the NRF52840: Programming, Antenna, USB, and Crystal

Jared — Thu, 23 Jul 2020 09:00:44 GMT

Hi,

Answers to your questions:

The nRF52 is programmed through the SWD interface which uses a SWDCLK line and a SWDIO line. You would need to route VDD and GND in addition to the SWD data and clock lines to a header (to make them externally available for a debugger). J-link is the debugger that we officially support so good choice. Also, our nRF52 DKs and nRF52840 DKs comes with an external debugger that can be used for programming custom boards. If you take a look at the schematic of the nRF52840 DK then you'll see that the SWD pins are routed to the onboard interface chip which acts as a onboard debugger.
The recommended values are just what we recommend as a starting point. You would either way at some point have to tune the matching network. Every matching network has to be adjusted (tuned) for that specific PCB. Thus, given that the nRF52840 DK and the Thingy are two different boards, then they would require two different matching networks. It seems that the misunderstanding is because you've assumed that the nRF52832 (which is the IC used on the Thingy:52) and the nRF52840 uses the same matching network for the radio. They don't! The matching network for the nRF52832 radio consists of a parallel capacitor and a series inductor seen from the radio. The matching network for the nRF52840 depends on the package but in most cases consists of a Pi-network + a parallel capacitor seen from the radio. To conclude, the Thingy:52 which uses nRF52832 has therefore the correct matching network as C3 and L1 is the matching network for the radio, while the C13, L5, L4 is the T-network for the antenna as described in it's datasheet.
The nRF52840 won't get hurt if you only power the USB interface but it would need to be powered through VDDH/VDD for the IC to actually work.
The crystals that they use on the nRF52840 DK is NX3215SA-32.768K-STD-MUA-9 and MP06003 and is listed in the BOM file.

Note: You can make a new ticket with your design files (schematic + Gerber/Altium files) for a review of your design from us!

Hope this helps with the sleep 🙂

best regards

Jared