nRF9151-DK not running from external power when USB is disconnected

[Oleg-AgamControl]

I’m using the nRF9151-DK Evaluation Board. Normally, I connect the board to PC via USB — for programming/debugging 

However, since I’m preparing for production testing, I need to check how the controller behaves without the USB cable connected.
So, I connected an external power supply to the board (instead of powering it from USB), and in the beginning everything functioned properly with this setup

But when I disconnect the USB cable, the controller stops working.

Question 1:
How can I configure the nRF9151-DK so that it keeps running from an external power supply only, without needing the USB cable connected?

During operation, I also connect external components via GPIO pins.

Question 2:
When the board is powered externally and the USB connection is not used, how are the GPIOs powered?
Do I need to supply VDD_GPIO separately in this case?

[Simon D-M]

You cannot power the whole DK with 3.5V, it was not made to do so. However, if you want to do current measurement, you can still do it.

To measure the current, you can do it with a Power Profiler Kit II (documentation), or if you don't have one, you can remove the jumper on P22 and input your 3.5V in the "VDD_nRF" pin (P22), but you still have to either connect the USB port or input 5V into the "VDD_5V" pin (P22). The nRF9151 will then be powered by your power supply and not by the 5V anymore. However, the GPIOs would still be powered by the 5V. (https://docs.nordicsemi.com/bundle/ug_nrf9151_dk/page/UG/nrf91_DK/measuring_current/prepare_board.html)

Best regards,

Simon D-M

[Oleg-AgamControl]

I understand your explanation, thank you.
My question is the following:

In the real hardware, when I use only the nRF9151 modem itself, the supply voltage available to me will be 3.5 V.
To which pins should I apply this voltage?
Is there a separate supply input on the chip for powering the GPIOs?

Also, could you please clarify what you meant by “However, the GPIOs would still be powered by the 5V”?
If you mean that only the on-board peripherals (like LEDs, buttons, etc.) on the Evaluation Board would not be powered without 5V, I fully understand that and it’s not a problem.

However, the chip itself should still be able to operate without 5V, correct?
For example, I have an application that sends and receives UDP packets over the network.
When I power the board with 3.5 V through the  "VDD_nRF" , it works — I can see the packets received on the server side.
But when I disconnect the USB cable, the communication stops.

In this scenario, I’m not using any GPIOs (at least not intentionally).
So why does the program stop working when USB is disconnected?

A more specific question:
On the actual PCB, there are two supply inputs — VDD and VDD_GPIO (pin 65).
Suppose I power the board with 3.5 V.
Can I apply the same 3.5 V from a single power source to both VDD and VDD_GPIO on the real PCB?
And can I do the same on DK board?

[Simon D-M]

Oleg-AgamControl said:

In the real hardware, when I use only the nRF9151 modem itself, the supply voltage available to me will be 3.5 V.
To which pins should I apply this voltage?

I highly recommend you checking our nRF9151 Hardware Design Guidelines it has most of the answers you are looking for. You can also look at the schematics from the nrf9151dk (link - go to "Downloads" and then "Hardware files").

Oleg-AgamControl said:

Is there a separate supply input on the chip for powering the GPIOs?

Yes. (link)

Oleg-AgamControl said:

Also, could you please clarify what you meant by “However, the GPIOs would still be powered by the 5V”?

The DK is powering the microcontroller through a power managment IC (nPM1300 PMIC). This IC is powered by the 5V/USB so all the things that are powered by this chip will still be powered by this chip. When you removed he jumper and put the power supply there, you basically put your power supply as the source power for the chip VDD (not the same as board VDD).

Oleg-AgamControl said:

So why does the program stop working when USB is disconnected?

Some peripherals (like the SIM card, the gnss module, ...) are powered by the nPM1300 so we can expect some peripherals not working when this chip has no power.

Best regards,

Simon D-M