USB power supply and additional external power supply

[student_adrian]

Hello,

in my application I want to power the nRF52840 with USB at the VBUS pin or a 3.3V external supply at the VDD pin.

I wonder what will happen if someone plugs in both, that there is supply at VBUS and VDD?

Thank you.

Adrian

[Marjeris Romero]

Hi Adrian,

Did you mean to use the USB lines and power the chip with an external 3.3V suply at the VDD pin at the same time?  Or do you want to connect VBUS to VDDH to power the nRF52840 in high voltage mode? I think you have to decide if you want to run the chip in normal or in high voltage mode.

Do you have a schematic drawing of how you plan to power the nRF52840?

Best Regards,

Marjeris

[student_adrian]

Hi Marjeris,

thank you for the answer.

I plan to either power the nRF52840 with USB power or external supply.

In some cases it can occur that both is connected.

Best Regards,

Adrian

[Marjeris Romero]

Hi Adrian,

Take a look at the reference circuit for nRF2840 at the infocenter for guidelines in how to power the nRF52840. If you want to power using 5V from USB you need to connect VBUS voltage to the VDDH pin (as shown in config nr 1). VDD can then be used as an external voltage supply VEXT to power other things in your circuit. You will then run the chip in high voltage mode. If you want to power from a 3.3V battery or external power supply you need to connect 3.3V to both VDD and VDDH pin, see config nr. 3. You cannot power the chip with 5V USB and 3.3V at the same time, since VDD will act as an external power supply in high voltage mode.

Best Regards,

Marjeris

[student_adrian]

Hi Marjeris,

I think I got it. I will connect 5V USB to VBUS and VDDH. Then I will use a step down converter of 5V instead of 3.3V for external supply and connect it to VDDH. Now I always run it in high voltage mode and the Controller doesn't care if both is connected.

Best Regards,

Adrian

[naveedshiliwala]

Hello Adrian

Did this work for you? because I have similar scenario,

1. The Board can be powered from 5V USB. 

2. The board can be powered from ext. supply 5V.

3. Both will be connected 5V usb as well as ext. 5V.

So do I connect the VDDH pin to both USB 5V i,e VBUS as well ext. supply 5V?

and incase both the supplies are connected wont USB 5V short with ext. supply 5V.

Kindly please revert as soon as possible,

Regard's

Naveed. 

[student_adrian]

Hello Naveed,

I don't work on this project anymore.

As far as I know it has not been tested yet.

Normaly you do have galvanic isolation between USB supply and ext. supply.

Best Regards

Adrian