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]

I didn't say only one of VDD and VDDH can be connected. I said only one of VDD and VDDH can be supplied and it says that in the spec sheet. That means you can't supply a high voltage AND a low one, you can supply one or the other. If you supply high VDD is unconnected, if you supply low you connect them together and apply the voltage there.

It doesn't imply anything of the sort. It just tells you you need to give it some kind of core voltage and VBUS itself won't just power the chip. You can give it <3.6v and connect VDD and VDDH or you can give it >3.6v on VDDH only. There's even an example of that.

I don't think the spec is unclear or contradictory but feel free to wait for Nordic to opine.

[CBSwift]

Yeah this is not true. I have used active designs that Tie VDD->VDDH, and power with up to 5.5V via VDDH or VBUS tied to VDDH no problem. Being tied to VDD as well seems not to bother the chip, but may not be "best practice."

[run_ar]

I would not recommend this, it means you are "bypassing" REG0 (the high voltage regulator) and inputing 5v5 volt to VDD which is rated to a maximum of 3.9V (Absolute maximum ratings). This will lead most likely shorten the lifespan of the device and lead to various unforeseen failures.