Different measurement between PPK2 Ampere meter and Source meter mode

[Md Mazedul Islam Khan]

I have already seen some topics about this, but still struggling to understand the correct measurement and difference between the PPK2 Ampere meter and Source meter mode. I used nRF 52840_DK with Thread: CoAP Server to measure the power using PPK2 in both modes, and I saw different numbers. The differences aren't even close to each other, and that's where I am struggling.

Source meter mode

Ampeter meter mode

As you can see, the average number of 26.24 nA for the Ampeter meter mode and 9.73 mA for the Source meter mode.

Why the huge difference? What am I missing?

Note: I am powering both of the devices through USB.

[Achim Kraus]

> I am powering both of the devices through USB.

That makes only sense with the "Amper meter mode", with the "Source meter", the device will have two sources. For that "Source meter" mode, please disconnect the device from USB.

[Md Mazedul Islam Khan]

Yes, in source meter mode, I never connect the device through USB as power comes from PPK itself

[Md Mazedul Islam Khan]

I kept the 'Enable power mode' turned on for both Ampere mode and Source meter mode. When I disabled the option 'Enable power mode' in Ampere meter mode, I see a different average number, which is 8.58 pA. But that's still a huge difference from Source meter mode where the number was 9.73 mA

[Achim Kraus]

> I kept the 'Enable power mode' turned on for both Ampere mode and Source meter mode.

That's well, otherwise it would not work.

> When I disabled the option 'Enable power mode' in Ampere meter mode

Does your target device run with that setting? If so, you have that second "power path".

Again, I use the PPK II a lot, I haven't observed a significant difference between source and meter mode. With that, I guess you have just a failure in your setup, e.g. a second "power path".

[Achim Kraus]

My UI shows "Enable power output", I guess, that's what you refer to.

[haakonsh]

Try this when using the PPK in source meter mode: 

1. Connect GND lead to any solid GND point on the DK.
   
   
2. Connect VDD lead to the top pin of P22.

We assume that you've cut SB40 and SB41 as described in the Measuring current chapter of the DK user guide.

[Md Mazedul Islam Khan]

Does your target device run with that setting? If so, you have that second "power path".

Yes, indeed since the power is coming from the USB that is connected with the device. In Ampere meter mode, PPK doesn't provide the power to the device, right?

So, I connect the device with USB in J2 port and that gives the device both power and has data access from computer.

I appreciate that for pointing out the second power path but I don't get since the Ampere meter mode needs the second power source through USB in the J2 port to run the device. If not, how the device will run without powering it up?

I must be missing something!

[Achim Kraus]

If "Enable power output" is off, and your device is still running, then your setup has a second "power path". Let me check the DK description, I guess you need to remove a jumper.

[Achim Kraus]

My understanding of the link from Haakonsh is, you need to cut a "solder-bridge".

You have two options VDD / VDDH (I' m not common with the difference), for VDD cut SB 40

(see https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_nrf52840_dk%2FUG%2Fdk%2Fprepare_board.html&cp=5_0_4_8_0)

for the measurement.

If you finished the measurement, you need a Jumper on P22 or you solder the "bridge again".

If you don't cut SB 40 (or the other), the device has two power paths, one through SB 40 one through PPK II and that makes your value that bad.

[Md Mazedul Islam Khan]

Now that makes sense. I had no idea that I have to cut something manually by hand. In that case, Source meter mode far more convenient but the situation puts me into a position where I need to measure the current in Ampere meter mode.

By the way, thanks to all of you for guiding the whole steps!

[Achim Kraus]

You're welcome.