nRF54L15 - System OFF : strange current peaks

[Patrick49]

I'm working with the nRF54L15-dk and with the system OFF sample available in https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/samples/boards/nordic/system_off/README.html with SDK ver 3.0.2.

Following this post :  abnormal current peak when system off (0.6mA) 

I measured the current with a digit multimeter DMM7510 on the P6 header on the dev kit. With either the wake on pin (GPIO interrupt) or the GRTC wake up (period = 10 s), I'm seeing those strange current peaks after about 3-4 seconds. I run the program without RAM retention.

They appear irregularly and seem to be cap at about 750 µA. 

What could be the cause of those peaks and how to get rid to them ? 

Best regards, 

Patrick

[Håkon Alseth]

Hi,

 

It is expected that you see a spike due to how the regulators behave in low power mode.

I do not know what your multimeters sampling rate is, but this can cause aliasing if the sampling freq is too low.

 

Is the overall measurement as expected?

 

Kind regards,

Håkon

[Patrick49]

Hello, 

I see. We can't to realy much about it, right ?
I used 0.01 NPLC on my multimeter. So I don't think there would be some aliasing problems. 

Yes the overall measurement is a bit higher than the datasheet but it's ok.

I have another issue with the system ON mode when the chip is idle. 

With my custom board

With the nRF54L15-dk

So when the device in on idle mode with system ON (2nd picture zoomed in), without any RAM retention or GRTC/GPIO to wake up, there are some peaks that appear regularly every 4 seconds. 
I found that it is caused by the RC oscillator calibration which happens by default every 4 seconds. Because, my pictures were taken on a custom board that doesn't include the LFXO, only the RC oscillator. So, maybe the nRF54L15-dk is using that LFXO oscillator to go into sleep mode and doesn't need to activate the RC oscillato hence no current peak on that period of sleep. 
I couldn't find any way to get rid of those peaks or to delay that calibration since the old answer were not on the nRF54L15 or an older version of nRF Connect SDK. 

Do you have any clue if it is possible to reduce those peaks ?

Thanks and best regards,

Patrick

[Håkon Alseth]

Hi Patrick,

 

Here are the expected sleep levels in different modes:

https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/chapters/current_consumption/doc/current_consumption.html#ariaid-title4

 

If you are 10 uA in SystemOff mode, this indicates that there is a problem with leaking GPIOs for instance.

You could for instance set the "INPUT" field in NRF_GPIO->PIN_CNF[n] to its reset value, which will internally disconnect the pin input buffer.

How is your setup on the actual DK when testing this?

In some cases, it is recommended to disconnect programming interface and the serial interface:

https://docs.nordicsemi.com/bundle/ug_nrf54l15_dk/page/UG/nRF54L15_DK/measurements/set_up_dk.html

 

Patrick49 said:

So when the device in on idle mode with system ON (2nd picture zoomed in), without any RAM retention or GRTC/GPIO to wake up, there are some peaks that appear regularly every 4 seconds. 
I found that it is caused by the RC oscillator calibration which happens by default every 4 seconds. Because, my pictures were taken on a custom board that doesn't include the LFXO, only the RC oscillator.

The wakeup to calibrate shall not be of high energy cost, it should be a smaller peak every 4 seconds.

Is your firmware rebooting on each wakeup? What is the current consumption in the 4 second idle period?

 

My question is: Is the SystemOn idle current matching what is shown in our datasheet?

 

Kind regards,

Håkon

[Patrick49]

Hello Håkon,

Håkon Alseth said:

How is your setup on the actual DK when testing this?

I tried the system OFF sample without the virtual com ports activated. I forgot to zoom in that picture, so the scale may be too big for the multimeter to give me some precise measurements. 

Håkon Alseth said:

Is your firmware rebooting on each wakeup?

Yes, I'm still searching a way to scan again without the reboot (cf my old post about discovering one service and then discover a new one that Edvin answered me) it's probably a discovery issue that I need to fix. 

Håkon Alseth said:

What is the current consumption in the 4 second idle period?

I didn't take a measure only on the 4 second period but on the whole sleep duration and I've got 5,2 uA.

But if I set up a longer sleep, I'm averaging at 4,7 uA (with 10 second of sleep for exemple).

Håkon Alseth said:

Is the SystemOn idle current matching what is shown in our datasheet?

So it seems a bit higher than expected on the datasheet since I only have a timer into a reboot to wake my system up, I don't really know which category to look at but it's probably the idle9 one since I don't use the LFXO in my custom board and that's the only setting that uses the RC oscillator. Did I make a mistake on that ?

Best regards,

Patrick

[Håkon Alseth]

Hi,

Patrick49 said:

So it seems a bit higher than expected on the datasheet since I only have a timer into a reboot to wake my system up, I don't really know which category to look at but it's probably the idle9 one since I don't use the LFXO in my custom board and that's the only setting that uses the RC oscillator. Did I make a mistake on that ?

It is a bit high (nom. 3.7 uA), but if you have other ICs and parts on your board, they will add to the idle current.

Your measurements show a approx. 3 uA static offset, which is usually due to external factors.

Did you follow the recommendations stated here?

https://docs.nordicsemi.com/bundle/ug_nrf54l15_dk/page/UG/nRF54L15_DK/measurements/set_up_dk.html

 

Kind regards,

Håkon

[Patrick49]

Hello Håkon, 

Yes, I did follow the recommendations to correctly measure the current. 

Håkon Alseth said:

3 uA static offset

That means that I should be able to get to the I_ON_IDLE0 state with my configuration ? I still don't know the details about that mode since I don't use the LFXO in my board. I was getting a current of 6.5 uA with the nRF54L15-dk for your information on that mode. I don't know if there is a function to disable all the non necessary peripherals in the board in order to achieve this level of current ?

Best regards, 

Patrick

[Håkon Alseth]

Hi,

 

If you try the sample here:

https://github.com/nrfconnect/sdk-nrf/tree/main/samples/zephyr/boards/nordic/system_off

 

What do you measure then?

 

Patrick49 said:

That means that I should be able to get to the I_ON_IDLE0 state with my configuration ? I still don't know the details about that mode since I don't use the LFXO in my board.

If you do not have a LFXO, you need to specify that you use the internal RC oscillator.

Patrick49 said:

I was getting a current of 6.5 uA with the nRF54L15-dk for your information on that mode. I don't know if there is a function to disable all the non necessary peripherals in the board in order to achieve this level of current ?

These are configured in the "Board configurator", which is a PC app that you can install via nRF Connect for desktop.

https://www.nordicsemi.com/Products/Development-tools/nRF-Connect-for-Desktop

 

Kind regards,

Håkon