ADC full-scale conversion in npm1300 Zephyr drivers

RE: ADC full-scale conversion in npm1300 Zephyr drivers

ovaneg — Fri, 08 Aug 2025 15:02:38 GMT

Hi Jared,

Yes, we are using a custom board.
I connected a battery and ran the ppk in ampere mode, which resulted in the same waveform as in source mode. Logging the current measurements from the npm1300 to compare, I was still seeing anomylous measurements compared to what is being measured by the power profiler.

However, I dont see us being able to resolve this issue without me being able to share details or schematics. Seeing as my original question regarding ADC full scale conversion has been answered, I will be closing this thread. If I continue to see differences between npm1300 and ppk2, I will open a seperate case as a private issue.

Thank you for your support,

Oscar

RE: ADC full-scale conversion in npm1300 Zephyr drivers

Jared — Fri, 08 Aug 2025 12:28:01 GMT

Hi,

Can you try to set the PPK in ampere mode and connect it between the battery and the nPM1300. What current do you measure now?

Also, is this on a custom board or are you are using the EK?

regards
Jared

RE: ADC full-scale conversion in npm1300 Zephyr drivers

ovaneg — Thu, 07 Aug 2025 16:18:17 GMT

Hi Jared,

Thank you for clarifying the ADC calculation.

Our board uses npm1300 to supply system power from a battery and measure battery current draw to report to the MCU. To connect the power profiler I replaced the battery with the ppk set up as a source meter, supplying power from the profiler instead.
I cannot share schematics, but other than the npm1300 there is nothing connected to the battery other than one extremely low power IC.

With this setup, I was periodically reading current from npm1300_charger (via Zephyr's regulator api) and logging the output. While monitoring current draw from the ppk on nRF Power Profiler (sampling at 10 kHz) I was comparing these results to current measurements being read and logged in Zephyr at 1 Hz and 10Hz (I tried different frequencies).
This set up gave the results I referenced in my initial post.

Regards,

Oscar

RE: ADC full-scale conversion in npm1300 Zephyr drivers

Jared — Thu, 07 Aug 2025 14:27:45 GMT

Hi there,

Latest documentation states:

A value of 01 means the battery is discharging. During a discharge, the full scale current (in Amps) is the battery discharge current limit (as configured in registers BCHGISETDISCHARGEMSB and BCHGISETDISCHARGELSB) multiplied by 1.12.

full_scale_ma = config->dischg_limit_microamp / 893;

Which can be rewritten:

full_scale_ma = config->1000/893 ~ 1.12

The latest driver version is a bit more clear:

		full_scale_ua = -config->dischg_limit_microamp *
				config->full_scale_discharge_factors[0] /
				config->full_scale_discharge_factors[1];

Where the scaling factors are defined here.

		config->full_scale_discharge_factors[0] /
				config->full_scale_discharge_factors[1];

= 1.12.

So the driver should be correct here.

I think the error is somewhere else in your system.

Can you explain how, or share schematics for your system?

How is the npm and ppk connected?

regards

Jared