nPM1300 IBAT current measurement

[AntonZ]

Hi!

For several days I struggle with the issue (if it is an issue) of the nPM1300 battery current measurement.
When the battery is charging the current value seens correct, but when it comes for discharging, I get either incorrect readings or 0 at all.
Even nPM PowerUP app shows "N/A" instead of current value when the battery is discharging (please check screenshot attached).
While making this screenshot I measured the current at the battery and it is 5.36mA.

Same behavior with the npm1300 example for Zephyr (NCS v2.6.2):

*** Booting nRF Connect SDK v3.5.99-ncs1-3 ***
nRF Fuel Gauge version: 0.9.2
init: V: 3.774, I: 0.000, T: 24.90, PMIC device ok
V: 3.764, I: 0.000, T: 24.90, SoC: 39.89, TTE: nan, TTF: nan
V: 3.764, I: 0.000, T: 24.90, SoC: 39.89, TTE: nan, TTF: nan
V: 3.774, I: 0.000, T: 24.90, SoC: 39.89, TTE: nan, TTF: nan
V: 3.769, I: 0.000, T: 24.90, SoC: 39.89, TTE: nan, TTF: nan
V: 3.769, I: 0.000, T: 24.90, SoC: 39.89, TTE: nan, TTF: nan

The strange thing I noticed is when I increase the current of the load connected to the BUCK2 to the value above approx. 10mA, current readings change to something above 0,
but still do not correspond to the values I get with the multimeter.

Looks like this behavior is not expected, but I just can't get the reason.
May it be some kind of HW or configuration issue?

Thanks,
Anton

[Tharaka]

Hi Anton

The integrated current measurement of the nPM1300 is designed to meet the Fuel Gauge algorithm's requirements and is not intended for use as an accurate current measurement. The lower accuracy in measuring small discharge currents should not affect FG performance, as the algorithm uses battery current, voltage, and the battery model ( also NTC temperature if available) to estimate the state of charge.

Discharge current measurement is relatively inaccurate below 10 mA, which is why we intentionally display it as NaN in nPM PowerUP. If needed, you can disable this option using the command in Serial Terminal:
shell:~$ npm_adc ibat_filter disable

If your device’s discharge currents are well below 200 mA, we recommend setting IBAT_LIM to the LOW setting as described here:
https://docs.nordicsemi.com/bundle/ps_npm1300/page/chapters/charger.html#ariaid-title11

In PowerUP that setting is available in the CHARGER tab

This adjustment will further improve current measurement accuracy and optimize fuel gauge performance at lower discharge currents.

Hope this helps

Regards, 

Tharaka

[AntonZ]

Hi Tharaka,

Thanks for the information.
I just could not believe that it is as you described.

So we have to keep it in mind when working with this PMIC.

Thanks,
Anton