nRF51422 radio issues

[Adrian Lita]

Dear Nordic,

I have built a board using nRF51422, and I've just manage to populate it and start it up. I'm using a modified example (peripheral_lbs), and everything seems to work ok (leds and buttons), but the radio isn't (I can't find it neither with my phone, nor with my laptop).

I've used the schematic as in 11.3.3 QFAA QFN48 schematic with DC/DC converter setup from the nRF51422 Product Specification v3.1. I also have the 32.768KHz osc populated, and the PCB antenna is built such as the one in PCA10028.

I power everything from a DC-DC converter which as an output voltage of 2.2V, and plenty of current if needed. I've measured the consumption, and it's around 0.5 mA, the same I had in PCA10028 while testing. So it pretty much behaves like the PCA10028, with the sole exception that I don't see it advertising.

I've checked the voltages on the VDD and VDDA, and they're 2.2V.

Can you give me some hints on how to debug this problem ? I think it might be something wrong with the board (maybe bad soldering, but I've checked under a microscope and everything seems ok).

Kind regards, Adrian

[Adrian Lita]

Thank you for the support. After long hours of debugging, I managed to find the problem. When I designed the board, I've put a certain 16MHz oscillator, but when I had to order, I found that wasn't in stock at that time, so I ordered another one with the same footprint. Unfortunately, the load capacitance was different. With the first one it was 16pF and with the second one it was 20pF.

I managed to see this when I touched the oscillator with my bare hands. Probably my skin acted like a capacitance between XL1/2 and GND, and that was the moment I've seen the board was seen by my phone/laptop.