nRF52840 BLE doesnt work

RE: nRF52840 BLE doesnt work

ketiljo — Wed, 15 Aug 2018 10:40:28 GMT

Ok, good. Now you know that the HW is working, but range is poor. This requires some layout work as I said earlier.

RE: nRF52840 BLE doesnt work

Sramota — Wed, 15 Aug 2018 10:18:10 GMT

Hello,
thank you, we tried change caps with caps 8.2 pF, but failed again. After that we changed crystal with capacitors from old board. We received advertise from the nrf52. We had bad crystal. Range is shorter and some mobile phones(Huawei) can not connect. Probably it is bad impadance maching circuit from the antenna.

RE: nRF52840 BLE doesnt work

ketiljo — Mon, 06 Aug 2018 08:33:21 GMT

For a 6 pF crystal, you need 8.2 pF load caps. Try changing those first and see if you can get the link up. The range can be shorter than optimal, but you should be able yo get a link with a few meters of range.

The antenna datasheet describes one possible matching circuit, you can use this one or the PI-network described in the whitepaper.

RE: nRF52840 BLE doesnt work

Sramota — Fri, 03 Aug 2018 14:02:00 GMT

The CL value of crystal is 6 pF.

Our PCB has 4 layrs. The inner layer unter top layer is GND, third layer is supply voltage.

Ok, if we will make new pcb, we will respect this paper. Now, but we need get our existing electronics to working state. It's any chance? What we can do now?

If we wil use antenna chip 2450AT18B100… Does we have to use matching circuit from this document https://www.johansontechnology.com/datasheets/antennas/2450AT18B100.pdf? (matching circuit for nRF+ matching circuit for antenna)?

RE: nRF52840 BLE doesnt work

ketiljo — Fri, 03 Aug 2018 13:31:33 GMT

What's the CL value of the crystal? You're using 12 pF caps, which indicates a CL value of 8 pF. The formula is Ccap = CL * 2 - 4 pF. With the wring cap value, the radio will be out of spec.

It's hard to see on the layout as the layers are stacked, but it looks like you are using only 2 layers. If so, you can not have any tracks crossing the RF section. The bottom side should be as solid as possible. Alternatively, use an inner layer as ground.

Use plenty of vias, at least one every 10 mm in both x and y direction to connect the two ground planes firmly together.

The matching network for the radio must be placed according to the reference layout, close to the radio. You need separate tuning components for the antenna, see this whitepaper.

RE: nRF52840 BLE doesnt work

Sramota — Thu, 02 Aug 2018 12:38:58 GMT

The PCB rev 2