Programm external board with 1.8V using nRF52840 DK

[Mechatroniker]

Hello Community,

I know there are already a few posts on this topic, but I wanted to make sure this is conform with my application.
I am trying to program an external board (with a nRF52840 chip) with the nRF52840 DK board, or with its J-linker.
I have included my connection diagram as a picture below.
The external board runs completely on 1,8V. That's why the external supply of the DK should be used.
For this I have connected SB36.

Is the connection of the two boards correct?
Do I have to make any settings to be able to program only with 1.8V? (Hardware or Software)

Many thanks in advance.

[Jared]

Hi,

Is there a specific reason for why you shorted SB36? It shouldn't be necessary, just make sure that you only supply one source at a time. The connection looks ok, just remember to supply the DUT externally with 1.8V.

Do I have to make any settings to be able to program only with 1.8V? (Hardware or Software)

regards

Jared 

[Mechatroniker]

Hi Jared,

Jared said:

Is there a specific reason for why you shorted SB36?

I read this in a blog and looked it up in the SB configuration afterwards. I have pasted the excerpt from this below. I just want to make sure when I have the 5V applied to J2 via the USB and the 1.8V applied via P21, that I don't get an overvoltage at the components and they don't get damaged.

With this configuration are all PIN's operated with 1.8V or are they still coupled to the 5V?

Jared said:

DUT

What do you mean by the DUT connection?

[Jared]

Hi,

Shorting SB36 will override the reverse voltage protection and can in the worst case damage the board if you have connected more than one supply at a time. In your case specifically, since the DK will operate at a different voltage than your DUT (device under test) then I think it would be best to supply your board externally. Do not connect VDD_nRF to VCC on your board, instead connect VTG to VCC on your custom board, and the rest as you have shown in your sketch. 

regards

Jared

[Mechatroniker]

Hi Jared,

I implemented your suggestion and powered my board with an external voltage source, which I also connected to GND Detect and VTG. I now get signals on the SWDCLK and SWDIO pins when I want to transmit something in Segger Studio.

My problem is that the signals on these two pins are given out with a voltage of about 3.7V (max), but my board has only 1.8V. Can I set this directly on the J-Linker? Most J-Linkers support 1.2-5.5V, so this should be theoretically possible.
Or do I need a external level shifter?

greetings

[Jared]

Hi,

I actually need to go back on what I said regarding programming at 1V8. The interface chip doesn't support.it after all. A level shifter might do the job but I haven't tested it myself, I think the best would be to just use an external programmer such as the SEGGER base EDU.

I'm very sorry for the confusion. 

best regards

Jared