Incorrect current measurements with PPK2 when using an nPM2100

[David]

Hello,

I am experiencing issues with the current measurements taken by the PPK2 when using the nPM2100-EK to power a device. The current drawn from the 2.7V power source (PPK2) is lower when using the nPM2100 (configured to output 3.0V) compared to a direct connection without the nPM. This is clearly incorrect. How should the PPK2 be configured to reliably measure our system, including the nPM2100?

The system is a Bluetooth-enabled measurement device that uses an nRF52840 chip. When connected to a Bluetooth master, the system draws an average current of around 530µA at 2.7V, which is quite high for a CRxxxx coin cell primary battery. Therefore, I would like to use the nPM2100 to boost the voltage to a constant value of 3.0V. However, when using the nPM2100-EK for this purpose, the PPK2's current measurement shows large spikes and an average value of only 320µA. As the nPM2100 does not generate energy, this measurement must be incorrect. 

I am using Power Profiler Version 4.2.2 and even a second PPK2 produces similarly incorrect results. I have read about the phantom spikes occurring at the highest sampling rate. I therefore selected a sampling rate of 10kHz, but the values are still incorrect.

Has anyone else experienced this issue? What is wrong with the PPK2 measurements?

[Vidar Berg]

Hello,

Do you have an an ammeter with sufficient resolution to confirm the average current draw? It seems strange that you are consistently measuring lower current when using a boost regulator with the PPK2 voltage source. The spikes you're seeing may be artifacts caused by the PPK2 switching measurement ranges during the charge/discharge spikes. However, the average current reading should still be accurate (within the PPK2's spec.). Are you planning to use a cr2032? Anyway, at least this size seem to be pretty resilient against normal current spikes from RADIO and CPU and allow you to utilize much of the capacity.

Best regards,

Vidar