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.

[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 !

[Stian Røed Hafskjold]

Hi, here in Europe (except UK) we are using comma as the decimal separator, so it's 1.5uA. I'm using a Power Analyzer to measure current which can supply voltage and measure current at the same time. So the green wire is a 3V output from the power analyzer on channel 2. And the yellow wire is channel 1 in ampere-meter mode.

In general it's hard to measure current in the uA range, you need to have equipment which can handle it. So first you need to figure out if the scope is actually showing you the right consumption. Do a test measurement over an unconnected resistor to see what the base current of the equipment is.

If it turns out that the current flowing into the nRF5 chip is actually 55uA when running the unmodified ble_app_pwr_profiling example, I don't really know what's wrong. Maybe the chip is ESD damaged or similar. I would suggest getting the newest version of the DK with a production ready version of the chip. The eng. A version of the chip is not recommended for new development anymore. The current consumption is different from the production silicon.

[Aamir]

Hi Stian,

Thanks for your answer,

As you suggested we verified that our instrument is capable of measuring into milli-amperes 

we measured 30 mV across 10K ohms resistor, which turns out to be near 3.1 micro amps 

On the subject of Eng A. we also have our company's proprietary board with Eng C. chips

so we measured the power profiling app on that as well, unfortunately, I can't show you the board but here is the measurement as taken on the oscilloscope

 

we got around 45 uA, which is very close to Eng A. chip on the development board. 

[Stian Røed Hafskjold]

Well, you need to measure over a 10 Ohm resistor. A 10k resistor will give you a voltage drop in the mV range. The questions is what happens if the voltage on the probe is in the uV range.

So two resistors in series with 3V across. One that limits the current to 3uA (1MOhm), and one 10Ohm measurement resistor. You should be able to measure the 30uV voltage drop on the 10Ohm resistor.