nRF52840 USB power ???

[Roger Clark]

Could someone explain how to power the nRF52840 via USB?

Looking at the schematics, and also reading the "objective" spec, I can see that VBUS is connected to the USB input bus voltage, and this voltage seems to be used for some of the internal functions of the nRF52840, via an internal regulator

But as far as I can tell, the internal regulator doesn't seem to supply the whole nRF52840, and an external regulator is needed for the VDD and VDDH

So, its the minimal USB configuration, VBUS connected to USB 5V, VDDH connected to VBUS and VDD supplied via a 3.3V regulator from VBUS ?

Or is VDD not required if power is supplied via VDDH ? As I was under the impression that the nRF52840 could run from LiPo etc without the need for an external regulator, but LiPo cells can be around 4.2V at top of charge, which exceeds the voltage in the spec for VDD

Can anyone clarify this for me?

[RK]

The product spec seems pretty clear on this no? If you want USB you need VBUS plus either VDD or VDDH. So the minimum config would be 5V connected to VBUS and VDDH with VDD unconnected so the chip goes into 'high voltage mode'. If you power through VDD you're limited to 3.6V but VDDH can be a lot higher.

The six example circuits at the end of the document show most of the obvious configurations including the one where the chip is powered entirely from VBUS (and where VDD is an output if needed). The 4th one shows the chip powered from a separate high voltage supply (eg LIPO) with VBUS just powering the USB and the 3rd one shows USB powered plus the rest of the chip from a low voltage VDD_nRF source.

The documentation also states that only one of VDD and VDDH can be supplied so not only is VDD not required if VDDH exists, it's not allowed. Look at the spec again, it's quite detailed.