Power measurement setup and the role of VDD in nRF52-DK

[PATA]

Hi all, 

Currently we are trying to measure the power of nRF52832 using (1) nRF52 DK board, (2) power profiler kit 2 (PPK2).

We used PPK2 in source-meter mode and we connected the pins as following:
(reference: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_ppk2%2FUG%2Fppk%2FPPK_user_guide_Intro.html)

1. VOUT (PPK2) &  P22-VDD_nRF (nRF52-DK) 

2. GND (PPK2) & P21-GND

We were testing system-off mode of nRF52832, which is expected to consume 0.3 uA.

However, in the above connection setup, we could measure around 600uA.

But if we connected an additional power supply to P21-VDD (external supply connector) and turned on the power switch (SW6), then we could measure the correct current of 0.3 uA.

I think we should be able to measure the correct current even when we are supplying power only to VDD_nRF (P22-VDD_nRF).

However, according to our experience, it seems like we need to supply to power the external supply pin of DK board (P21-VDD) to get the correct measurement result.

I'm wondering if it is correct.

If it is correct  I'd like to know the reason why we need to supply to get the correct measurement result.

Also, I'd like to know the role of VDD (not VDD_nRF) in DK board.

P.S. We have used not only PPK2 but also source meter unit (SMU) to measure the power, but we could get the same results regardless of equipment (either PPK2 or SMU).

Thank you.

[Stian Røed Hafskjold]

Hi the nRF52 is connected to the debugger chip through the SWD interface as well as the nRESET line. If the voltages don't match there will be leakage current. Or if the debugger chip is not powered at all, the nRF52 will power the rest of the DK through these lines. That's why you can't just power the nRF52 on the current measurement header.

Another thing to note is that if you power the DK through a USB cable and measure the current going through the current measurement header, there will be an additional 10 uA because of the 1 kHz noise on the USB.

So you have two choices.

1. 1. Power the nRF52 on the current measurement header, P22, using the PPK2 in SMU mode.
   2. Connect the USB cable to power the rest of the board
   3. Make sure that the voltage out from the PPK2 matches the VDD voltage exactly. It should be around 2.7V
2.  
   1. Power the DK on the external supply header, P21, using a stable power supply at 3V
   2. Measure the current going through the current measurement header, P22, using the PPK2 in ampere meter mode.

Method 1 is the easiest, as you don't need to plug in the USB cable every time you want to flash a new FW.

Alternatively, if you want to change the voltage, you can use method 1 but then you will have to cut the solder bridges that connects the nRF52 to the debugger chip. You can always use an external debugger if you want to flash the nRF52 later.