PPK2 wrong amplitude for current spikes

[cazaugg]

I try to use the PPK2 to measure current of a MCU in sleep. The board has some caps and a coin cell to keep the RTC on chip alive. It wakes up every 1 second to check wake up conditions.This naturally causes the a current spike. The amplitude of this spike is what i am trying to measure.

Here is where the problem comes in. The current spikes, the PPK2 measures are impossibly high. I added 10k Resistor in series before the PPK2 (amperemeter mode) to check the values using a scope. The spikes are way too high, up to 3mA.

When adding the shunt in series after the PPK2 the values are reasonable: 10uA - 15uA

This should no bee the case, it looks like the PPK2 is supplying power in ampere meter mode. 

Is there anything im doing wrong? Why is this?

Thank you for your help!

[Kresimir]

Hello,

I can not be 100% sure, but I think the problem is with the PPK2 auto range control. When the current is small, PPK activates the large shunt resistor. Then the current suddenly rises, but PPK remains at a large shunt resistor for some time before switching to a lower value. 

PPK is not bad, but it cannot be fixed in a single range. This is a problem when the current is dynamic.

Once again, I am not an expert for PPK, but it seems this can be an issue.