Unexplained current spikes during sleep

RE: Unexplained current spikes during sleep

Simon D-M — Mon, 27 Jul 2026 13:55:32 GMT

Hi,

If I recall correctly, I tried to run the application on multiple other MCUs (nRF54L15, nRF52840, ...), and it only happened on the nRF52DK, so I would guess it only happens on the nRF52832 (probably also on nRF52810, nRF52805 as they are based on the same silicon).

And as you put the nRF52840 as an example, I just re-tried on the nRF52840 DK just to be sure, and I don't see any spikes.

Best regards,

Simon

RE: Unexplained current spikes during sleep

Will_20241202 — Mon, 27 Jul 2026 12:23:04 GMT

Huh. That's unfortunate, but I suppose better to have a fix than the risk of the RTC not functioning properly.

Is it known whether this same bug affects other controllers (e.g. nRF52840)?

RE: Unexplained current spikes during sleep

Simon D-M — Mon, 27 Jul 2026 10:41:59 GMT

Hi,

The spikes are actually expected. They are caused by a fix for a potential HW bug concerning RTC bit corruption in the nRF52832:

For nRF52832, the default RTC bit width is 15 instead of 24. This is related to some RTC bits being possibly corrupted. This could be overridden by changing CONFIG_NRF_RTC_COUNTER_BIT_WIDTH, but the Kconfig is not user-selectable intentionally, counter’s oldest bits may not work properly.

For the default bit width of 15 and RTC prescaler of 0, the counter wrapping happens every 1s. At the same time, RTC driver’s logic limits scheduling to half of counter span because of uint math. Hence, the CPU is awake every 0.5s. The shorter intervals seem like an offset of the one set in main.c, which is in different phase from the steady 0.5s driver’s intervals.

And if we consider that the spikes are smaller than what they seem (due to the PPK2 switching range) the price to pay for that fix is still quite small and reasonable.

Best regards,

Simon

RE: Unexplained current spikes during sleep

Simon D-M — Tue, 21 Jul 2026 12:59:18 GMT

Hi,

[quote user="Will_20241202"]I can rule out a PPK2 ranging issue since that would appear in both the old and new builds of the software on the same board.[/quote]

The root problem is indeed not a PPK2 ranging issue. I was able to find the commit that introduce the issue (link) using "git bisect" on the SDK. I've reported it internally, I'll get back to you when I have more information about it.

But PaKa is also right in the sense that you shouldn't trust the number that are displayed on the spikes. The fact that you are seeing much higher spikes than me is probably cause by the PPK2 ranging behavior, and the real peak current is likely much lower.

If you want to check the actual peak current of the spike, then as Paka said previously, you need an shunt resistor and a oscilloscope. The PPK2 is not the right tool for that.

Best regards,

Simon

RE: Unexplained current spikes during sleep

Will_20241202 — Tue, 21 Jul 2026 12:20:51 GMT

I do not believe this is the case because the exact same board/hardware, using an older SDK build of the code does NOT exhibit these spikes. So the culprit must lie in the software/firmware/configuration difference between the two, not in a hardware issue.

I previously tried switching from the DC/DC to the LDO per one of the AI suggestions and saw no change, which also suggests that the spikes are not caused by the capacitor refresh.

I can rule out a PPK2 ranging issue since that would appear in both the old and new builds of the software on the same board.

Trying another AI suggestion, I also made sure that the 32kHz source was set to an external crystal _AND_ that the recalibration period was increased from 4 to 64, but the periodicity/amplitude of the pikes was unchanged.

Per Simon's post above, it seems to be something introduced in the NCS 3.2.0 that did not exist in prior versions.

RE: Unexplained current spikes during sleep

PaKa — Tue, 21 Jul 2026 08:10:57 GMT

Potentially two separate issues here:

1: When the nRF52 goes into the lowest power mode then the regulator goes into refresh mode. This means it has close to 0 power consumption all the time but when the voltage drops too low it will recharge the external capacitor. This is seen as a very short, high spike in the power consumption. This is normal and not an issue. This spike is in the single digit mAs normally.

2: When the PPK2 sees very low power consumption it automatically changes it measurement range downwards, this is done by changing the measurement resistor. When you then get the real current spike, this resistor will be changed to accommodate a higher current. This may in some cases make a larger spike than actual show up in the plot, this is an artificial artifact caused by the measurement circuit. It does not impact the average current as it evens out over time, the PPK2 will still be within spec with this.

If you want to make sure the spike is real and not the artifact then the solution is to use an oscilloscope to check the real height/width of the current spike, remember to use your own shunt resistor for this.

You can also enable a low pass filter in the PC fronted to remove these spikes, they are in the advanced menu of the Power Profiler app. Note that this is just changing the display and not the data measured and averaged.

RE: Unexplained current spikes during sleep

Will_20241202 — Mon, 20 Jul 2026 16:13:16 GMT

Thanks Simon. Unfortunately my spikes are significantly larger, many in the tens of milliamps range so they are not something we can ignore (this is a VERY power sensitive battery project so every wasted joule adds up quickly).

If I change the main loop code to just sleep for a really long time, then the spikes go back to being periodic at almost exactly 500ms (give or take a few milliseconds). Every once in a while there are two spikes within a millisecond of each other. I notice this phenomenon in the scree capture you posted as well.

The amplitude I see is still in the milliamp to tens of milliamps range though, so not sure why yours are so much smaller than mine.

RE: Unexplained current spikes during sleep

Simon D-M — Mon, 20 Jul 2026 15:51:39 GMT

Hi,

I was able to reproduce your isse on a nRF52DK. It seems like this behaviour only appears from NCS v3.2.0 onward.

I also have the spikes but mine are significantly smaller, and every 500ms exactly. Are you also seeing this frequency ?

And from what I can see, the difference between having the spikes and not having them is around 0.2uA. So not much.

And these spikes are already very likely exagerated by the PPK2 as it has to change measurement range and tries its best to output a value. But during the change the PPK2 is known to be very inaccurate and outputs much higher values than they really are.

Even though, I'll try to see if I can find anything more on it, and I'll also ask internally if someone knows something about it.

I'll keep you updated.

Best regards,

Simon