Unexpected consumption using System OFF Sample & nRF52840DK

[clockis]

Greetings,

I have been measuring the current consumption of our custom FW in our custom board using PPK2 and found some unexpected spikes in the current consumption curve.

I decided to look deeper into this so programmed our custom FW to the nRF52840 DK and the behavior remained the same.

Finally I decide to test some samples with absolutely no changes on the nRF52840DK to confirm the normal behavior of the current curves I should see when the system is Active, in Sleep (system ON Idle) & finally System OFF(which is irrelevant for my application).

It seems that flashing the nRF System OFF sample (unchanged, as it was in the NCS) to the nRF52840 DK produces the same current curve. As mentioned in other tickets ( I have searched and read all of the relevant ones in existence) the current curve in System Sleep (with UART off) should be a few tens of microamps but I am consistently getting the current curve shown below.

Connection diagram (PPK2 in Ampere mode) 
I have also measured with the SW6 to the DEFAULT and nRF ONLY positions but the results were the same.

!!!Below you can see the current curve for the nRF52840DK flashed with the nRF System OFF sample and focus on the duration that corresponds to the System Sleep (System ON Idle) part of the duration ( the sample enters the SYstem Sleep state for two seconds, this what is shown below)

System Sleep (System ON Idle)

System Sleep (System ON Idle) the curve shown above ZOOMED IN ( to be able to distinguish the spikes)

The whole current curve for the System OFF sample

I have tried all different methods of measurement using the PPK2 (Ampere mode & Source mode by providing the external supply from the PPK2) but in all instances, I am getting the same current curve(shown above).

I have also tried the beacon sample (with no changes/modification, as is) and gotten the same curve in Idle mode (apart from when the device wakes up to advertise), between the advertising events I get the same spikes up to 3mA with the current never falling bellow 100's of microamps.

Beacon sample

Beacon sample ZOOMED IN

Even more ZOOMED IN

According to other tickets as well as this one that contains current curves for the Beacon sample this is not at all the Normal curve I should see for this sample

(this is what the people in the ticket mentioned report as the normal current curves for this sample)

which is completely different from my curves.

What could be the cause for the behavior and current curves I am observing when loading the nRF System OFF & Beacon samples to the nRF52840DK and measuring using the PPK2?

Please get back to me for any further information needed, I can also provide the data for the curves shown above.

I look forward to hearing from you.

Best regards,

Stavros

[runsiv]

Hi Stravos 

We are about to enter Christmas vacation on support, so the support will be slow/limted until start of January. 
Just to verify. Is the DK prepared for current measurement as it is described in the Current measurement guide?

I would also recommend to not power the DK over USB when you do current measurement as it might affect the measurement. 

Regards

Runar

[clockis]

Hi runsiv,

A kind reminder, for any updates or information about this would be very helpful as this is a critical issue for us.

I look forward to hearing from you.

Best regards,

Stavros

[Vidar Berg]

Hi Stavros,

Sorry for the delayed response. Could you please try programming the hex file attached below and measure the current draw on your 52840 DK? Preferably in source mode, as this tends to produce the least amount of noise in the measurements in my experience.

system_off_demo.hex

Thanks,

Vidar

[clockis]

Hi Vidar,

Thank you for your response, I have tried the image you sent on the nRF52840 and measured the power consumption using the PPK2 in source mode and connected to the P21 External Supply header of the nRF52840DK while the SW6 was in the nRF ONLY position.
The resulting current curve (shown below) has been compared to the nrf system off sample with no modifications at all and it is apparent that the image you sent me corresponds to the nRF52840 entering the System Off mode and not the System Sleep(System ON Idle) which is the mode I am trying to troubleshoot.

system_off_demo.hex

system_off (nrf sample unchanged) System Off portion of the current curve


Unfortunately, the System Off mode is irrelevant to us as we do not use it the issue is with the consumption and current curve found when the sample goes into System Sleep (System ON Idle). Could you please provide feedback for the correct current curve that I should see when the device is in System ON Idle (with UART OFF)?

Currently using the sample of nrf/system_off I get the following current curve when the device is in System Sleep (System ON Idle).

Is this correct? Is this what I should see when the device goes into System Sleep (System ON Idle)? 

Note: all measurements were performed in source mode and connected to the P21 External Supply header of the nRF52840DK while the SW6 was in the nRF ONLY position

Thank you and I look forward to hearing from you!

Best regards,

Stavros

[Vidar Berg]

Hi Stavros,

Your meausrements are a bit high. The picture below shows what I measured with the system_off_demo.hex on a nRF52840 DK here.

And this is what I measured for system ON mode on the same board (hello world sampel built with CONFIG_SERIAL=n):

system_on_demo.hex

Typical system current in System ON and System OFF are documented in the Current consumption chapter of the product specification.

Best regards,

Vidar

[clockis]

Hi Vidar,

I used the sample system_off_demo.hex you sent, how is it possible to have different measurements with higher consumption using the same application and board? What could cause this? Could you share the setup you used to do your measurement? How is the PPK2 connected to the nRF52840DK (what header?) and what is the positions of the switches (SW6, SW10, SW8, SW9)? 

Also could you please use the nrf/system_off sample for NCS v2.1.0 and post the current curve you get for the System ON Idle portion of the sample ( nrf/system_off sample for NCS v2.1.0 goes into busy wait for 2 seconds then busy wait for another 2 seconds with the UART off, then 2 seconds on System ON Idle and then System ON Idle with UART OFF for another two seconds before going into System OFF), I am interested in the bold portion of the execution.

Also, I tried the sytsem_on_demo.hex you sent in your previous comment and I am again getting a different current curve from yours, how is this possible when we are using the same .hex file and the same board?

system_on_demo.hex (SW6 - nRF ONLY , SW10 - ON , SW8 - OFF , SW9 - VDD ) External Supply = 1.8V

I am aware of the typical current consumption values which is why I am trying to make sense of these measurements and find a way to properly measure current consumption using the Nordic samples ( with no modifications) to be able to be sure about the measurement setup and to reproduce the values mentioned in the datasheet, but I have not been able to reproduce these values using the nRF52840DK and the Nordic samples(unchanged) or using the images you sent me as you can see above, what am I doing wrong?

Thank you and I look forward to hearing from you.

Best regards,

Stavros

[Vidar Berg]

Hi Stavros,

Here's a picture of my setup:

Where the switches are put in the following positions: SW6 - nRF ONLY , SW10 - OFF , SW8 - ON , SW9 - VDD.

Please try to replicate my setup as shown above to see if you achieve better results. It's possible that your current setup is measuring more leakage. Since you are using the same hex files that I built, this should not be an issue related to the firmware configuration.

Best regards,

Vidar 

[clockis]

Hi Vidar,

Thank you very much for your immediate reply!

I just loaded the system_on_demo.hex you sent to the nRF52840DK (using the nRF Connect Programmer app)  & then set up the PPK2 & nRF52840DK as you mentioned ( all switches in the positions you mentioned and Supply Voltage to 3.0V as in your screenshot) 

 

The current curve I got is shown below

which is still very different from what you are getting. What could be the reason for this?

Thank you!

Stavros

[Vidar Berg]

Hi Stavros,

I see that the USB is not connected, please try plugging it in. Also, have you cut the solder bridge next to P22? From your picture, it appears to be shorted with solder.

Best regards,

Vidar

[clockis]

Hi Vidar,

I plugged the USB to the nRF52840DK and to my PC and I get the measurement shown below

Vidar Berg said:

Also, have you cut the solder bridge next to P22? From your picture, it appears to be shorted with solder.

I previously used the PPK2 in Ampere mode to measure the current so I needed to cut the SB40 (as the screenshot from the guide you posted suggests) so for this measurement I shorted it again (using solder) as the nRF52840DK would not be powered at all if I didn't, is that not correct? The nRF52840DK Guide (pg. 38) also mentions this.

Best regards,

Stavros

[Vidar Berg]

Hi Stavros, 

The solder bridge (SB) must be cut when measuring current. Otherwise, the nRF52840 will be powered by the USB-to-3V buck regulator when the USB is connected. Also, with the SB shorted, the PPK voltage applied on P22 may be fed into other parts of the board's circuitry, which should not be included in the measurement. 

I recommend using a jumper, as it allows you to easily switch between current measuring mode and the regular mode.

Best regards,

Vidar