NRF52840 / board bring-up / DEC5 = 0V

Hi there,

We have just received a second set of boards based aournd the NRF52840. 

The first lot was fine, but we are not able to flash those news boards. So it is really hard to investigate what the problem is... 

One thing I have noticed is:

  • even though everything else is powered
  • DEC5 stays stuck to ~0V on the faulty boards (the 1.3V is generated OK by DCC) 
  • Is that a symptom of something else going wrong in the chip? at start-up maybe? or ESD?
  • On some boards (but not all) DECUSB also seems not to start...  

Another idea I had was:

  • Maybe my crystals dont start 
  • But my understanding from the datasheet is thatm during flashing, the NRF52840 is running on its internal clock source. 
  • Can you confirm that as well? 

Thanks for your help,

Mickael