I am working on a project where the nRF52840 is used in USB powered mode. That means that it is normally supplied with 5V at the VDDH pin. In this case the nRF52840 generates internally its own VDD which is software adjustable and per default set to 1.8V according the datasheet.
But now the problem: the SWD programmer we want to use only supports 3.3V.
No matter which voltage I supply on the VDDH pin - before first programming the internal voltage regulator will generate 1.8V for VDD so that 3.3V at SWD pins would be much too high. I think the nRF52840 would get destroyed in this case.
So I got the idea to supply directly the VDD pins of the nRF52840 with an external 3.3V supply just for programming. But in normale voltage mode VDD and VDDH should be connected together according the datasheet - however they are not connected together in my design because in normal operation the nRF52840 will be supplied in high voltage mode with 5V at the VDDH pin.
Does anyone have an idea how to solve this problem?
What would happen if I just supply the VDD pins with 3.3V without connecting VDD and VDDH together?
Thank's a lot in advance for your help!