Power Profiler showing negative current for external DUT

[_armin]

Hi,

I am using the Power Profiler Kit (Rev. 1.1.1.) with Power Profiler app (v2.3.1) to measure power consumption on an external DUT. The issue I am facing is negative current values shown by the Power Profiler app when I set the PPK output (regulated) voltage to around 2 V or less. Negative values are shown when nRF chip on my DUT is in low-power mode, and when it is not in low power mode (e.g. advertising) it seems to give logical measurements. If I set the output voltage to more than 2 V, I get currents of 4-5 mA or more while my DUT is in low-power mode, not sure what is the cause of this, but I would like to at least resolve the issue of negative idle currents with low output voltage.

My test setup is as follows, taken from the PPK User Guide:

- PPK stacked on top of a nRFDK52840,

- The nRFDK52840 connected to the PC with a USB cable,

- Power Supply switch on the PPK set to Regulator position,

- Power Select switch on the PPK set to External position.

Note that there is no battery or another power source connected to the DUT, it is powered solely from the PPK.

I have found a similar issue on the DevZone, and the answer here is that PPK cannot be stacked on top of the DK when using the voltage regulator (if I understood it correctly):

https://devzone.nordicsemi.com/f/nordic-q-a/59474/power-profiler-showing-negative-current

Besides this, an answer to another questions suggests that PPK has to be powered through the DK, because USB supply on the PPK is faulty:

https://devzone.nordicsemi.com/f/nordic-q-a/36162/power-profiler-graph-is-in-negative-region-and-average-current-also-appears-to-be-negative

Please advise on how to proceed with measuring the consumption of an external DUT.

Thanks,

Armin

[_armin]

Hi, I have tried the one where PPK uses USB for power supply, and I am getting different, but still bad results. Now the current is always shown to be in the range of 5 to 10 mA while in low-power mode, instead of going below zero like before (when I lower the voltage).

The link I posted earlier seems to suggest that USB supply is faulty on the PPK, so not sure if trying an external power supply would help? I could try that if there is reason to believe it can work, but it is a little inconvenient so would like to avoid doing it if it cannot be helpful.

Here is the link regarding the PPK USB power supply again:
devzone.nordicsemi.com/.../power-profiler-graph-is-in-negative-region-and-average-current-also-appears-to-be-negative

Any other ideas on what else to try?

[Jared]

Hi,

The thing is that if you're going to use the PPK on top of the DK then the PPK voltage should match the DK voltage. If it doesn't, you risk current leakage and erroneous current readings. I suggested configuring the connection as in the figure in my previous reply since the voltage of the external DUT didn't match the DK voltage. It seems that you don't longer have negative current readings but still measure a higher current then you expected. Now, what application are you running on the DUT when you measure? And what do you mean by low power? System OFF or System ON IDLE? 

[_armin]

Hi, it is System ON IDLE.

Can you please confirm that the link I posted is irrelevant for my issue, and that the PPK can actually be supplied from USB:

If the PPK USB supply is faulty, then there is no point in trying this setup for measurement?

[Jared]

Hi,

The answer from my colleague was related to an older version of the PPK. The issue should not be present in current versions. 

regards

Jared