Power configuration 4 and external DCDC

[Tiit]

Hi

I'm currently using power configuration example nr. 4 for my custom board with nRF52840. Can I use external DCDC for powering my other components on the board (SPI and i2C devices + some GPIO Pin-s with pull-up and pull-downs) with described configuration? Would external pull-ups or downs to external VDD cause problems? I use same voltage for both VDD-s (3.3V).

Actually I see, that configuration type 5 would be better suited for my board (my other components draw more current as internal DCDC can handle), but I should be sure about current version before I ask for changes in board layout.

[Bendik Heiskel]

Hi,

There's no issue using  external DCDC converter for the other components on the board, but you need to make sure the VDD voltage of the nRF52840 is the same as the external DCDC.

By default, when using REG0 with VDDH as the supply for the SoC, the VDD voltage will be 1.8V, if you want to use another voltage for the external components and pullups, you need to change the output voltage of REG0 using the UICR register REGOUT0

 

If the external DCDC converter can supply enough current, it is easiest to change to configuration 5 and supply the nRF52840 from the external DCDC.

 

Best regards,

Bendik

[Tiit]

Ok .. good, but when I use with example nr. 4 internal pull-up / pull-down mixed with external .. would that be OK?

[Bendik Heiskel]

Using both internal and external pull-up  or pull-down at the same time is not recommended. The internal ones should be disabled when using external ones.

[Tiit]

No .. I actually mean, if I need to put some additional pull-up or down for some GPIO line that has no external resistor and same component already has external resistor on some other GPIO line.

I have strange current leak on my custom board -- I have SPI e-paper, that is powered from external DCDC. Our board configuration is so, that MCU internal DCDC output has nothing connected (only SWD socket for programming, because NRF52840 from factory has 1.8V VDD and I can't flash it straight from the box with DK without powering the MCU with 3V from SWD socket).

If I flash the board, then e-paper gets power from somewhere and is active. Therefore I tought that some internal pull-up is maybe giving parasitic power via SPI or something like that.