Supply only my nrf52840 with minimum power consumption

Question

Hello! 
 
 I'm a beginner with Nordic products and I'm taking over the nRF52840 Preview Development Kit. 
 
 I want to send advertisings at regular intervals (every second). Between advertisings, I want to go in sleep mode. To do this, I used the following example program, with some minor changes: 
 <InstallFolder>\examples\ble_peripheral\ble_app_beacon. I used nRF5 SDK v14.1.0 and S132 softdevice. 
 
 I want to put an external power supply that consumes a minimum of energy, to power directly my nRF52840. My software must obviously continue to work. 
 
 I tried to put the external power supply (3V) on the P21 connector (Switch SW6 is on “nRF only” / Switch SW9 is on position VDD). But, I consume about 2.6mA, which doesn't correspond at all to sleep mode... If I measure on connector P22 with a good multimeter (with SB40 cutted) , the current consumption is about 2uA in sleep mode, as desired. 
 
 Where should I put the external power supply for minimum power consumption only (some uA in sleep mode)? Do I h ave to modifie other switches or solder bridges? 
 
 Thank you in advance for your answers!

Alpha · Accepted Answer

I am currently working the same problem, what I found helpful is the following: 
 http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52/dita/nrf52/development/nrf52840_pdk/direct_supply.html 
 It says: "Since it is only the nRF52840 SoC that is supplied from this source, it is recommended to supply the VDD domain from a different source (coin cell battery or USB) to prevent the pins of the SoC to be connected to unpowered devices. To prevent leakage due to voltage differences, the board should be set in the nRF only mode." 
 For me this is the solution and resulted in a current drain of a few uA. 
 If you do not want to deal with all of this you need to create your own PCB with only a nRF and your power supply.

Bjørn Kvaale · Answer

Hi, 
 Sorry for the delayed response. I believe this devzone case could be useful for you. If you set SW10 located on the bottom left of the board to nRF instead of VEXT, you bypass everything on the board apart from the nrf52 chip. Also, remember to plug in the USB cable even if you power over P21. This is to ensure that everything else on the DK works like it should. Then, you should get similar values over P22 compared with P21. 
 Hope that helps!

Supply only my nrf52840 with minimum power consumption

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