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

[Jack.Batter]

I have made a custom board using NRF52832 (NRF52832-QFAA-R/QFN-4) with 32MHz and 32.768 kHz crystal. The SDK is nRF5_SDK_17.0.2_d674dde. It can be connected using nRF52840 Dongle ( https://twcn.rs-online.com/web/p/wireless-adapters-wifi-dongles/1769054 ). The blinky peripheral can connect and toggle the LED. But the custom cannot even be scanned by NRF connect on the android phone (Sony Xperia 5, Samsung A20 SM-A205GN, Sony X Compact F5321, Sony XA1 G3125). The same program and softdevice put on SparkFun nRF52832 Breakout (https://www.sparkfun.com/products/13990) can be scanned by dongle and phone. I have also try to bypass the regulator and give 3.3 V to NRF. But the problem is still there. Does anyone know what this problem can be?

Schematic (Core)

Demo (connect by dongle)

Key component list
QANTEK 32MHz Crystal ±20ppm SMD 2-Pin 5 x 3.2 x 1.1mm ( https://my.rs-online.com/web/p/crystal-units/813-6148/ )
TXC 32.768kHz Crystal ±20ppm SMD 2-Pin 3.2 x 1.5 x 0.75mm ( https://my.rs-online.com/web/p/crystal-units/753-7265 )
Antenna: YAGEO CAN4311153002451K (http://www.farnell.com/datasheets/48853.pdf)

The detail file folder
https://drive.google.com/drive/folders/1Z-ACsJZp1kQs0VzaHMHi2R6-ipInSnWG?usp=sharing

[ketiljo]

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. 

[Jay Tyzzer]

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.

[Jack.Batter]

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.

[Jack.Batter]

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!