Power Profile Kit II doesn't show current value when it is testing the current in GND

[huapage]

I am testing the current consumption of SIM cards with PPK2.

When PPK2 is connected to VCC ( voltage 1.8 v or 3 v ), the PPK2 can display the current properly ( around 9 mA ).

But when PPK2 is connected to GND ( voltage 0 ), the PPK2 cannot display the current properly ( display as 1 mA, but actually it should be 9 mA ). With oscilloscope I can see correct current value.

PPK2 current measurement cannot work properly in low voltage?

Application Version is 4.1.2

[huapage]

I tested with the following setup.

Power VCC (5V) --> 500 ohm resistor (R1) --> PPK2 VIN --> PPK2 VOUT --> 0 to 100 ohm adjustable resistor (R2)  --> GND

The R2 is used to avoid the voltage of PPK2 VOUT is same as GND, then the test result will not be correct.

While adjusting R2 from 0 ohm to 100 ohm, it seems that when R2 is increasing, the PPK2 test result will become more accurate, then at around R2 is 470 ohm and the PPK2 VOUT is 0.442 V, the test result will be correct. You can see there is spike in the wave form, after that spike, the test result is correct.

Can you check why there is a spike? Also any workaround for this PPK2 wrong test result? If no workaround then need to at least give user a warning that if PPK2 VOUT is less than 0.442 V ( Or some more accurate value you can get), the test result may not be correct.

Because some users may assume PPK2 test result is correct and use that data as reference then it may cause issue. ( If they don't use multimeter or oscilloscope to double confirm ).

For this static current case, use multimeter can double confirm. But for dynamic current case, need to use oscilloscope and some resistor to double check. It needs extra work. If can correct in PPK2 level it will be better. If cannot, need to tell the user the limitation of the PPK2 current measurement.

[hmolesworth]

My best guess is that VDUT - which is the measurement of VOUT using a 120k and 30k resistor divider - gives a VDUT voltage of 88mV when VOUT is 0.442V and 88mV is close to nothing and subject to issues, especially when reducing further as R2 is decreased. I imagine Nordic would simply say - quite reasonably, in my humble opinion - that this is outside the specification of the PPK2 which is designed to measure the current consumption of nRF parts in operation, which don't work at all below a volt or so; the PPK2 was never intended to be a general purpose multimeter.

As an aside, given that the PPK2 measures the DUT voltage VOUT, it would be most useful if that value were available as several users in this forum have requested. Nordic?

Edit: I forgot to add the specification, which as you say is needed; Nordic defines minimum voltage (on VIN input) as 0.8V: "For the ampere meter mode, an external power supply must source VCC levels between 0.8 and 5V to the device under test (DUT). For the source mode, the PPK2 supplies VCC levels between 0.8 and 5V and the on-board regulator supplies up to 1A of current to external applications."

Power-Profiler-Kit-2

[huapage]

Hi Swathy,

With the setup described, do you have any comments?

Especially the test case of Power VCC (5V) --> 500 ohm resistor (R1) --> PPK2 VIN --> PPK2 VOUT --> 0 to 100 ohm adjustable resistor (R2)  --> GND, when you increase the R2, there is a spike when R2 is around 47 ohm. After that spike, the test result becomes correct.

Thanks,

Huang Weichao

[huapage]

If PPK2 cannot measure correctly when VOUT is in low voltage, at least in UI need to show a warning to tell the user the measure may not be correct so that it will not misleading the user.