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?

[Roger Clark]

Where does it say that only one of VDD and VDDH must not be connected? (just in the USB section ?)

Looking at page 68 of the spec, in Figure 10 ("Normal voltage mode, LDO only") and Figure 11 ("Normal voltage mode, DC/DC REG1 enabled"), it shows VDD and VDDH connected together.

There is a configuration where VDDH is not connected to VDD

Later in the USB section it says

"As a consequence, both VBUS and either VDDH or VDD supplies are required for USB peripheral operation."

Which implies that when used with USB, that VDD can't be connected to VDDH (like in the other diagrams)

But I'd like clarification from Nordic, as this is only version 0.5 of the spec, and appears to be contradictory or just unclear.

BTW. Re: VDD as an output when VDDH is an input. I can't see a max current value in the spec for IEX as this only seems to be quoted for "IEX,OFF" not IEX,ON