I’m using the RAK4631 schematic as a reference but I can’t see what’s the connection of the VDD_NRF signal from the RAK4630. Below is the schematic, in green I’ve marked the parts related to the VDD_NRF, R4 and R8 are supposed to connect VDD_NRF to a supply but both are marked as NC (not connected).
I also check these two resistors in a RAK4631 board and they aren’t soldered.
In the RAK4631 board, I also tested continuity between VDD_NRF and every contact in the WisConnector, but no connection seems to exist, so no voltage is being applied to VDD_NRF, is that correct?
L10 is always soldered and the RAK4630 stamp module as it is sold is not built for single 3.3V supply.
The power supply connections as shown on the RAK4631 schematics are the ones that should be applied when using the RAK4630 stamp module on a custom PCB.
I think that the Recommended Operating Conditions should follow the real operating conditions.
In my way of understanding why VBAT_NRF can’t be 3.3V I guess the nRF52840 is internally using the High Voltage mode and the output for REG0 (buck converter) is configured to 3.3V, so the input voltage (VDDH → VBAT_NRF) has to be higher than that.
VBAT_NRF requires a voltage in the range 3.7V - 4.2V
VBUS can be left unconnected if USB is not being used.
Any other supply can be tied to 3.3V
Only for curiosity, If is it correct that the output for REG0 is configured for 3.3V, is there any reason that no lower voltage was chosen for that? So that a single 3.3V external voltage supply could have supplied everything in the RAK4630?
But reading this post makes me think of removing R5 on my PCB. My custom PCB is manufacturing right now and I expect to come on a week.
I’m using LiFePo4 battery on V_BAT3V6 flag, and a step down regulator on 3V3_REG flag, probably my error was no email to RAK Wireless before manufacturing… let’s see… BTW I have also a footprint for RAK11720 on this PCB
Dear @nicolasech
Many thanks for the advice, I’ve received my custom PCB’s and tested removing VDD_NRF. At the moment the module works without problems. I’ll keep the forum updated if I find something weird.
Sorry guys and @carlrowan to hijack this thread but I have the same concern (RAK4630 with custom PCB full powered with 3.2V or 3.6V depending on battery we put ), let me know if I missed something