RAK4631 + RAK19007 & RAK19011 gpio output voltage

Hi, we have RAK4631 module on a RAK19007 and RAK19011 base boards. We’re facing an issue with GPIO output voltage, when the pin is set to high, instead of 3V, we’re getting 2 to 2.4V on any of the available pins (IO1, IO2, TX, RX) on the baseboards. What could be the reason for this?

Hi @sefermemic ,

If it happens on both baseboards, it a appears to be a supply source issue or there could be something wrong on RAK4631. I doubt it is the latter though.

Where do you get the power source for your setup? Also what voltage does it provide? Are there any other connections aside on the core and the baseboard?

We have UWB and accelerometer modules as well, but we tried without them, same results. We are powering the base boards with Li-ion battery, but also plugging in the USB on 19007 doesnt make any difference

The problem seems to be VDD_NRF, which is anywhere between 1.8 to 2.5V, and the output GPIOs have the same voltage when set to high. It varies depending on the current consumption, at least from what I can tell. If I put nRF52 to sleep and disable UWB and accelerometer, VDD is around 2.5V, but if I don’t put nRF52 to sleep, and enable everything else, it drops down to 1.8V. Or it’s anything in between, depending on what I have enabled.

VBAT_NRF is measuring ok, 3.6V.
VDD on the baseboard is 3.3V.
Exposed 3v3 pin for J-Link in RAK4631 is also measuring 3.3V.
VBAT_SX is 3.3V.
VBAT_SX_IO is also 3.3V.

Any idea why VDD_NRF would not be 3.3V?

Hi @sefermemic ,

The GPIO voltage level is dependent on the VDD_NRF.

The level of VDD_NRF depends on the mode of operation of the nRF52840 inside RAK4631.

If you are using RAK4631, it works on High-voltage mode and the VDD_NRF is set by the REGOUT0 register.

What firmware are you using? It appears to me that you use a custom firmware.

The 1.8V you see could be the default state of the REGOUT0 register.

@carlrowan That fixed it, I was not aware that nRF52 was in high voltage mode on RAK4631. Thanks.

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