Current measurement unexpected 50mA baseline

I recently started using the otii and I use it a lot, it gives me great insight in the current consumption of my electronics.

I have a problem with measuring the current from a battery powered wireless device that has an onboard booster (MAX17224ELT+) to boost the voltage from 2xAA alkaline (2-3V) to 3.3V. Sometimes, 1 out of 5-10 times, when I turn on the power switch of the otii (set to 3.0V and 2A over current protection) the current immediately starts with a baseline of 50mA and on top of that is the normal current current profile of the device (MCU). The otii is powered from a benchtop power supply (7V 3A) on the DC barrel jack on the back side. When I power my device directly from the benchtop power supply, I don’t get the 50mA baseline current. I am not sure where exactly is the problem. I can hardly believe it’s the microcontroller or other circuits on my board. I suspect the booster is the problem but only when connected to the otii. Inrush current is less than 180mA.

Have you seen similar problems before? Could it be series resistance in the power supply of the otii? Or maybe some interaction between otii power supply and my booster? Does the otii have a switching power supply? Or an LDO? Can I see the power supply circuit? Should I use thicker or more solid power supplies cables? Should I add filters or a LDO to the otii power supply?


Could you attach a recording when this behaviour occurs and one when it doesn’t?
This would help a lot in trying to understand what is happening.

Best regards,

[SOLVED] The problem is not the Otii because it also happens when I supply my device directly from a benchtop power supply. Thanks

Hi Bjorn,
First I thought the problem was with the otii. Then I found out I have the same problem when the device is pwoered from external power supply. Then I thought I had found a workable solution, I added a large capacitor to the booster input. That was when it was powered from benchtop power supply. But now I powered it from the otii and I see the problem again. So I think the problem could be related to the power supply wiring. Maybe inrush current, series resistance and cables inductance causes the booster to go crazy. Do you have any thoughts? Have you seen anything like this before?

Sounds like an instability issue.
Put a scope on the input and output. Use low impedance probing techniques (i.e. the little spring GND thing that came with the scope probes). Once you can see what the input and output is doing, you should be able to address the issues you are seeing.
Its most likely Cin or Cout and/or layout…