nRF51822 external capacitor between AVDD(35/36pin) and VSS(33/34)

[???]

Hello,

I have a question regarding AVDD(35/36) pin. I am using nRF51822 QFAA package. And the reference circuitry on the datasheet uses a 1.0nF capacitor between AVDD and GND.

We have the following questiongs: When I put 1nF capacitor on my board, the bluetooth will always disconnect probabilisticly. Then measuring the AVDD waveform by oscilloscope ,the wave on AVDD is as large as 800mV when advertising. But when I change the capacitor from 1nF to 4.7uF,the wave on AVDD reduce substantially,and the Bluetooth connection become more stable.But now,I'm afraid it will introduce new problems.

So if I put a 4.7uF capacitor instead of 1.0nF capacitor, would it affect the Bluetooth signal for advertising? I want to know how serious it would cause a problem for the system if used 4.7uF instead of 1.0nF capacitor in that place.

[FormerMember]

The problem may be related to the power supply. What does your schematic look like? Do you have followed the schematic for the DCDC-converter, by using C12, L4, and L5?

It may work to replace C9 by a 4.7 uF, but that will not be optimal. It is better to make sure that the DCDC-converter is connected correctly.

[???]

I use the schematic for Internal LDO，the DCC pin is NC.The Schematic is as follows.And my PCB is double layers. According to the schematic and PCB Layout,could you give me some suggestions on the C9(C10 in my files) ?

[FormerMember]

If using the internal LDO, you should follow the reference layout without the DCDC connected. It means that VDD1 in your schematic should have one decoupling capacitor of 100 nF.

Which 16 MHz crystal do you use? And what are the value of the corresponding decoupling capacitors? Is their value calculated according to the formula in this tutorial?

Could you upload a layout that also shows the ground layers?

[???]

PCB_GH3100_MB_V1.0_Layout_20160620.pcb

I used the 32MHz crystal with 12pF decoupling capacitors. Then the value is followed by the Reference Design.But I measured the wave of crystal by oscilloscope,it was OK.

Then the Layout is attached.Could you help me to check it? Thanks very much!

[FormerMember]

In which "editor" should I open this file?