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.

[Bendik Heiskel]

Hi,

The only option for using the onboard debugger and a VDD voltage of 1.8V is to configure the SoC for high voltage mode. In high voltage mode the on-chip regulator REG0 supplies VDD to the nRF52840, the output of this regulator is by default 1.8V but can be configured by writing to the UICR. On the nRF52840DK high voltage mode can be used by setting SW9 to either Li-Po or USB.

When the switch is set to Li-Po the input to REG0, VDDH, is supplied from the Li-Po connectors J6 or P27.  This input voltage can be in the range 2.5V to 5.5V.

When the switch is set to USB, VDDH is connected to the 5V line from the USB connector J3. So when using this configuration a second USB cable must be connected to J3.

 

The reason for not being able to use external 1.8V on P21 and the onboard debugger is that a voltage regulator supplied by the 5V from J2 is used to supply the interface MCU. When SW9 is in the VDD position the 3V output of this regulator is connected to both to VDD and VDDH. When using the external supply on P21, J2 must not be connected.

 

Best regards,

Bendik