NRF52 current peaks

[genis]

I am seeing strange current spikes when measuring the consumption in a nRF52 chip. The board the chip is on is a custom board, but the nRF52 power supply has been isolated so its consumption can be measured alone. I didn't flash any soft device and I'm running the simplest of the programs to enter System OFF mode.

int main(void) {
    NRF_POWER->DCDCEN |= POWER_DCDCEN_DCDCEN_Msk;
    NRF_POWER->TASKS_LOWPWR = 1;
    NRF_POWER->SYSTEMOFF = POWER_SYSTEMOFF_SYSTEMOFF_Enter;
}

Still, I see spikes of current at about 3.5Hz with max current peaks of about 13-14mA. See images below (sorry about the narrow yellow spikes):

The only explanation I can think about is that it may be caused by the refresh modes of the current regulator, as explained in some other posts in this forum. Anyway that's a very unclear feature to me and I can't find anything about it on the nRF52 product spec. Also those peaks I'm measuring are really high and very often.

Anyone any thoughts about this?

[MartinBL]

I had a chat with our current measurement guru, and it is indeed possible that it's just the refresh mode you are seeing. The height, frequency, and pulse width of the current spikes that is caused by the refresh mode depends on:

1. The current drawn by the nRF52. Higher current consumption -> more frequent pulses.
2. The size of your decoupling capacitors. Larger capacitances -> wider spikes.
3. The internal resistance of your decoupling capacitors. High resistance -> wider spikes.
4. The internal resistance of your power supply. Low resistance -> high spikes.

If you had an ideal power supply (without internal resistance) and ideal decoupling capacitors (also without internal resistance) your current spikes would be infinitely high and infinitely narrow.

So while your spikes are in the high end of what we usually see, the periodicity of them is a strong indicator of this being the refresh mode in action.

[genis]

Sorry for the late response. I'll see if I can test different decoupling capacitors and see what effect has on the refresh mode.

[MartinBL]

Great! Please keep us posted.