PCA10056 - need 1.8V SPI levels while still having PC USB connection for programming

[32bitBanger]

I'm using PCA10056 (nRF52840 DK) for a project. First-time user, so little experience with this board.

I need 1.8v level SPI signals from the PCA10056 since I need to talk to a peripheral board which uses 1.8v level.

By default, my SPI is currently 3.3v level because I power the PCA10056 over USB (i.e. the USB3 programming cable going to the laptop).

How can achieve 1.8v SPI levels on PCA10056 to match my peripheral board?

I was thinking of using external power of 1.8v on 'Exteranl Supply' P21. Would that work? Is it still safe to keep the USB connection to laptop for programming (USB IF MCU jack J2)? Will the 5V on that connector get isolated away from the 1.8v VDD?

Thanks in advance for any help.

[32bitBanger]

Hi Bendik,

Thanls for confirming the following:

Bendik Heiskel said:

When using the external supply on P21, J2 must not be connected

But now I wonder if we're missing something. Please see https://devzone.nordicsemi.com/f/nordic-q-a/59679/using-the-nrf52840-dk-with-1-8v-io where Rob asked exactly the same question 2 years ago. I only found this after I posted my question here.

In that ticket, Simon replied to Rob with "Please try the following setup: SW10 set to ON. USB connected to J2. SW9 set to VDD. P21 powered from an external 1.8V supply. SW6 set to default." and Rob confirmed that works.

So he's using external power 1.8v on P21 **AND** using J2 for program/debug at the same time without problem ???

Best, Dave

[Bendik Heiskel]

Hi Dave,

I completely forgot about SW10. The solution suggested by Simon works, when SW10 is in the on position the onboard 3V regulator is disconnected from VDD.  Allowing you to supply external 1.8V to the nRF52840 while using the onboard debugger through J2.

 

Best regards,

Bendik

[32bitBanger]

OK. That's great news. So happy it's a supported configuration