PCB Reference Ciruitry

[josh_s]

I am new to pcb design so forgive my questions:

I see the reference circuitry for the nrf52840 and some PCB guidance around the nfc antenna design, but I haven’t found any explicit specifications for things like pad size, via-in-pad diameter, etc.  Am I to assume that the recommended workflow then is to work with a reference design alone without other documentation and specifications?

I see all the nrf52840 references circuitry are 4 layer, while the usb dongle is 2 layer. My use case is pretty simple, so is it fair to skip the reference circuitry and rather base my design off the usb dongle since its 2 layer and overall more simple?

I’m still experimenting with which reference circuitry fits my use case, so I wish I had a very very simple breakout that literally just exposes all 70+ nrf52840 pins with no other components, so that I can stick it in a breadboard and rapidly adjust the design. Is this super naive on my part or is this a worthwhile wish given that I’m still exploring.  The issue with this is the fanout is actually tricky for a novice like me due to the via-in-pads.

Thanks in advance.

[Bendik Heiskel]

Hi,

 Am I to assume that the recommended workflow then is to work with a reference design alone without other documentation and specifications?

We recommend staring with the reference design files that can be downloaded form the product page, and modifying it to suite your application.

We have a whitepaper with PCB guidelines for the aQFN73 package used for the nRF52840: https://infocenter.nordicsemi.com/topic/nan_040/APP/nan_040/nan40_intro.html?cp=16_1

I see all the nrf52840 references circuitry are 4 layer, while the usb dongle is 2 layer. My use case is pretty simple, so is it fair to skip the reference circuitry and rather base my design off the usb dongle since its 2 layer and overall more simple?

The nRF52840 dongle can be a good staring point for a  2 layer board, but not all of the GPIO pins will be available with only 2 layers. The inner row requires the use of via in pad, and on a 2 layer board this will impede the ground connection for the center pad.

I’m still experimenting with which reference circuitry fits my use case, so I wish I had a very very simple breakout that literally just exposes all 70+ nrf52840 pins with no other components, so that I can stick it in a breadboard and rapidly adjust the design. Is this super naive on my part or is this a worthwhile wish given that I’m still exploring.

Creating a simple breakout board for all the pins will not work, all the external components in the reference schematic must be placed close to the chip. The RF path from the ANT pin to the antenna must have an impedance of 50Ohm, any incontinuities like a pin header, in the trace will result in reflections of the transmitted/received signal which will reduce the RF performance.

For development we recommend using the nRF52840-DK. All the GPIO pins are broken out to Arduino compatible headers, allowing for easy development with external components.

 

We can review your PCB design, to help with finding mistakes before the boards are produced, just create a private ticket and share the design files with us and one of our hardware engineers will give you feedback on the design.

 

Best regards,

Bendik