Debug missing USB power detection on custom board

[Tobias P]

I designed a prototype custom board with the nrf52840 (QIAAD0).

It has a USB socket, with an external LDO supplying 3.3V to VDDH + VDD (following the recommended circuit configuration from the manual under "Figure 212: Circuit configuration no. 3 schematic").

I can flash and debug it with a J-Link debugger, the USB interface however seems to be nonfunctional.

The debugger shows a value of 0 at 0x40000438 (USBREGSTATUS), which I interpret as VBUS detection not working.

I measured the following (at vias close to the MCU):

- 3.25V at VDD and VDDH

- 5V at VBUS

- 0V at D+/D-

I guess this is somehow a fault of my board design, but I'm a bit at a loss how to debug this further. Any advice would be appreciated.

[Tobias P]

Polite ping. It'd be nice to have some information how to debug the USB power situation.

I'm leaning towards fixing the RF problem by simply using an off the shelf module, but that leaves the USB question - and I guess it might be useful to other reads of this forum, too.

[Marjeris Romero]

Hi Tobias,

I am sorry for the late reply. I took this case from Jonathan who is out of office right now.

Have you measured VDD with a multimeter? Could you send me a pdf file of your schematics? It looks like I am missing some kind of library in kiCAD because I am not able to see the connections to your external LDO right:

Best regards,

Marjeris