NRF52832 custom board can be connected by NRF dongle but cannot identified by phone

RE: NRF52832 custom board can be connected by NRF dongle but cannot identified by phone

Jack.Batter — Fri, 30 Oct 2020 14:37:49 GMT

Thanks Jay.

I will take your advise for the pi network.

DEC4 is a typo but it is connected.

I will add cap to reduce RF noise.

Many thanks!

RE: NRF52832 custom board can be connected by NRF dongle but cannot identified by phone

Jack.Batter — Fri, 30 Oct 2020 14:00:11 GMT

Thanks ketiljo. It work like a charm.

I just replace the C3 and C4 with 20 pF cap ( CL = [20 pF+ 4 pF] / 2 = 12 pF, near the required 12.5 pF of TXC 32.768kHz Crystal)

And I replace C1 and C2 with 30 pF cap ( CL = [30 pF+ 4 pF] / 2 = 17 pF, near the required 18 pF of QANTEK 32MHz Crystal) but exceed the C_{L_HFXO} maximum 12 pF NRF52832.

Finally, it can be connected by all my phones. I guess the root cause is the incorrect load caps that pull the crystal frequency.

I will replace 32 MHz with another CL 8 pF crystal to meet the spec of NRF52832.

Thanks a lot.

RE: NRF52832 custom board can be connected by NRF dongle but cannot identified by phone

Jay Tyzzer — Wed, 28 Oct 2020 16:16:17 GMT

A antenna matching network is missing. It is good to have a pi network near the antenna feed.

DEC2 output is declared as DEC4 on the Schematic. I don't know if this is a problem with the layout program.

P0.25 and P0.26 should either be grounded if not used or have a 12pF cap to ground on each pin as shown in the reference design. This is to reduce some RF noise from leaking out those pins.

RE: NRF52832 custom board can be connected by NRF dongle but cannot identified by phone

ketiljo — Wed, 28 Oct 2020 14:11:03 GMT

The reason is the 32 MHz crystal. The load capacitance is 18 pF according to the link. Max load capaictance for the nRF52832 is 12 pF so the crystal is out out spec: https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/clock.html#unique_1749008215. The oscillator can't drive this so you must find a crystal with a lower CL value.

For both crystals, you must calculate the load capacitors like this:

Ccap = CL *2 - Cpin, where Cpin = 4 pF.

The 32 KHz crystal have CL = 12.5 pF. So C3 and C4 must be 20 pF each. Using incorrect load caps will pull the crystal frequency.