Softdevice high idle state power consumption

[Aamir]

Hi, 

I am using nrf52840 Preview - DK, with SDK v15.3.0 and Softdevice API 6.1.1

I have modified the 'ble_app_blinky' example to have an advertising interval of 500ms and turned off the NRF_LOG by setting the NRF_LOG_ENABLE and NRF_LOG_BACKEND_URAT_ENABLE to 0 in the sdk_config file.

I have measured the current using an ocsilloscope and I am not getting the idle current (3 uA)a s described on the online power profiler, I entered the the following parameters in the online power profiler 

nrf52840, voltage 3, DCDC off, internal RC, Radio power 0 dbm, advertising(connectable), Tx payload: 31 bytes.

also we have not connected the oscilloscope  in the manner shown in the documentation, but we used one probe and connected it one pin of nrfCurrent Measurement and the other one to it's ground (reference). because when we were connected it in the manner shown in documentation we were not able to see the waveform. 

Please, tell me how can I achieve 3 uA idle current consumption. 

scope_5.scp

I have attached the '.scp' file that has the respective readings

[Aamir]

This is how we have connected the oscilloscope. 

[Stian Røed Hafskjold]

If you are connecting the scope like this you must be sure that ground on the scope is not connected to the same ground as the development kit. Otherwise you will short the USB power / power supply to ground.

I can't open the scp file. Which program do you use to open it?

So what is the idle current you measure?

Which value do you use on the measurement resistor?

Try to connect an amperemeter/multimeter on the measurement header (remove the resistor) instead of the scope. It's easier to setup and you can use it as a reference for your scope-setup.

[Stian Røed Hafskjold]

Yes this is less than version 1.0.0

Can you try to measure with a multimeter instead of the scope?

So is the 50 uA based on the 290uV RMS value? You have to use average value, not RMS.

Are you sure the accuracy of the scope is in the uA range?

[Aamir]

the RMS value is fluctuating quite frequently, the moment I captured the above picture it was showing 290uV but it mostly remains aroung 500uV that is why I said 50 uA

We measured it with multimeter and we got around 270 uA 

and on the oscilloscope, we switched to Average and the value is fluctuating very much it is even going into negative values

[Stian Røed Hafskjold]

Are you sure that the ground potential on the scope is completely isolated from the DK? Did you try with a multimeter?

[Aamir]

Yes, the ground on scope is isolated from DK

and we measured it with a multi-meter, we got around 270 uA 

[Aamir]

Hi Stian,

is there anything else we can try to measure the power consumption ?

[Stian Røed Hafskjold]

Hi, not sure what is wrong. The ble_app_pwr_profiling is starting in system OFF mode. I see you have version 0.9.2 of the DK which has the first engineering version of the chip (Eng A), I think? It has lots of bugs and system OFF current should be around 1.5uA.

Here's my DK setup:

• Supply power to the P21 "external supply" header (3V).
• Set SW10 (VEXT->nRF) to the ON position
• Keep USB cable plugged in
• Set SW6 to nRF ONLY
• Set SW9 in VDD position
• Measure current over P22

Green wires are supplying the power and the yellow wire is measuring current

And here's the current measurement running the ble_app_pwr_profiling hex. Green plot is current going into the green wire, and same with yellow.

[Stian Røed Hafskjold]

Can you check that the chip is eng A (QIAAAA markings on the chip)? On engineering B (QIAABB) the regulator was never able to fully go into low power mode (ULP) if I recall correctly, so if you have this version it could explain the high idle current you are seeing.

You should get the newest version of the DK, since a lot has changed since the first engineering samples of the chip.

[Aamir]

Yes, I have Engineering A chip the markings on the chip says 

NRF52840 QIAAAA 1716AK 

aside form this DK I also have our company's proprietary boards, with markings saying

NRF52840 QIAAC0

I think this is engineering C chip, can this chip be used to verify the  power consumption ?

[Stian Røed Hafskjold]

Engineering C is the same as revision 1, the newest chip is revision 2 (eng D). You should be able to verify the consumption on the eng C samples.

[Aamir]

Hi Stian, 

Sorry for the delayed reply, I was out on business trip

I have some of questions,

In your setup, you are using Green wire as 3V external supply, how are you measuring it on oscilloscope ?

In the oscilloscope snapshot you posted, I see can see the marker 1 at 1,505uA and 2,487 uA , both the readings have a comma(,) in them, doesn't that correspond to 1.5 mA and 2.48 mA ? and same with maker 2 and average current.

and we replicated your setup and this is the results we got

our oscilloscope can't measure current directly, so we take the reading across a 10 ohms resistor, which in this case measures around 55 uA. Can you please take a look at this and tell me what's wrong? 

Thanks !