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.

[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

[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.

[Roger Clark]

DIdnt you say "The documentation also states that only one of VDD and VDDH can be supplied"

[Roger Clark]

Not that this really matters.

I'll just connect VBUS to VDDH via a diode, so that if I just want to power via VDDH it doesnt back feed into VBUS

I know, I can't connect VDD to VDDH if VDDH is power via LIPO

I will leave VDD unconnected to label it as "BAT" for battery input

I'm adding all the external DC/DC components for battery usage as well.

But I'll get Nordic to check the circuit, in case this is not allowed when powered via VBUS/ VDDH