nRF5280 PDK Floating VDD_nRF_SENSE

RE: nRF5280 PDK Floating VDD_nRF_SENSE

ketiljo — Wed, 24 Apr 2019 09:31:56 GMT

I agree that R88 should be populated, I'll forward the feedback.

RE: nRF5280 PDK Floating VDD_nRF_SENSE

sas — Fri, 12 Apr 2019 14:11:00 GMT

Ketiljo,

SW10 is ON:
1. Yes you were correct, there is no power to nRF52840. But Interface MCU is still powered. This is the expected behavior I think.

VDD_nRF_SENSE is floating:
1. Unfortunately I don't have the right tool to install R88. But I confirm that when I shorted both pad of R88, my laptop can communicate with the PDK smoothly., I can detect the board using lsusb command, I can download the code to nRF5280 chip.
Shorting R88 pads means pull Q2 gate low, on which pull U17_ENABLE high and at the same time pull U16_ENABLE low. No doubt add R88 should fix VDD_nRF_SENSE floating.
2. I believe this is not a good practice to left Q82 gate, which is VDD_nRF_SENSE, floating. If it is, then why nordic didn't populate R88? I saw some thread setters asking why suddenly their computer can not detect PDK. I conclude populate R88 is the solution to their problem. Cmiiw.

Thanks,

RE: nRF5280 PDK Floating VDD_nRF_SENSE

ketiljo — Fri, 12 Apr 2019 12:03:57 GMT

If switching SW10 to ON, the power supply of nRF52840 is routed directly to P21 (External supply) connector, as long as SW9 is in VDD position. With no power supply on P21, nRF52840 has no power and it is reasonable you could not connect to target.

Some thoughts:

The 1.5V you see is most likely that the nRF52840 gets reverse powered through some GPIOs.
This will have some diode drop to VDD_nRF.
The VDD_nRF is then fed back to VSRC_nRF through SW9
VSRC_nRF connects to VDD_nRF_SENSE through SW10
VDD_nRF_SENSE then activates the voltage follower U19 and activates the switch U16 which has an EN threshold voltage of 1.1V
With VDD_nRF_SENSE floating when SW10 is switched to OFF might leave the voltage “hanging” there.
You could try to populate a resistor on R88, 1M ohm or so to see if U16/U17 switches correctly then.

RE: nRF5280 PDK Floating VDD_nRF_SENSE

sas — Fri, 12 Apr 2019 03:26:32 GMT

additional note:
I think my question related to nRF52840-PDK USB not recognized problem.