Online power profiler - current consumptions differ from datasheet

[alfiero]

Hi all,

I was trying to evaluate the nRF52840 current consumption through the online power profiler. I set the tool as in the below image

there are three standby currents: one after crystal ramp-up, which is of 1.6 mA; the other two, just after the RX state, are of 2.2 mA.

I cannot find in the datasheet (v 1.1) these current consumption states. I've checked in the sleep, CPU running, and receiving/transmitting sections (see below this message).

what these standby current consumption are related to? Also, what post-processing current consumption of 2.1 mA (the last part of the graph) is related to?

Moreover, if I wanted to consider a sensor reading stage via I2C, before BLE event, what could be the current consumption that I should consider (I'm referring to the nRF52840 power consumption, not considering the sensor, of course)?

Thank you so much in advance for your help!

[Stian Røed Hafskjold]

Hello!

I cannot find in the datasheet (v 1.1) these current consumption states. I've checked in the sleep, CPU running, and receiving/transmitting sections (see below this message).

These currents are part of the clock tree current. They are not documented because it's very hard to calculate what these currents will be. It is completely dependent on what other things are running on the chip. And we cannot state simply one number. Because of this we have chosen to include selected current measurements scenarios in the PS which are the ones you have posted above. These include the necessary clock currents. It's also why we have the online power profiler tool which will fill in the gaps in the PS.

The current after the crystal ramp-up is the crystal run current plus some parts of the HF clock tree.

The current between the RX and TX and at the end is the HF clock run current plus some CPU processing. The CPU processing varies, so the average current within one block in the power profiler will also vary.

Moreover, if I wanted to consider a sensor reading stage via I2C, before BLE event, what could be the current consumption that I should consider (I'm referring to the nRF52840 power consumption, not considering the sensor, of course)?

The Softdevice sleep current is given in the online power profiler at the top. It's called "Idle current". So this is the current you will get before the BLE event. Then you have the sensor reading itself which uses I2C. The I2C will consume current while it's active. I'm not sure why this is not documented. But the run current of the I2C is 1.2mA in LDO mode, and 900uA in DCDC mode. This is only during the transaction.

[alfiero]

Hi Stian!

thank you for your answer.

So basically, I can consider the BLE event average current for the time period indicated by the online power profiler, then the I2C (in my case DCDC) average current for another time period and finally the idle current (which is summed to the I2C sensor idle current) and I can get average power consumption. I will neglect the power consumption between nRF wake up and i2c transaction, unless you have hints about this.

Thank you so much!

[Stian Røed Hafskjold]

Yes, that sounds like a good plan.

 

alfiero said:

I will neglect the power consumption between nRF wake up and i2c transaction, unless you have hints about this.

This depends on how you are starting the I2C transaction. If you are using the RTC timer to schedule the I2C transaction, so that you just start and stop the transaction right away you will have a sleep current similar to the BLE sleep current in the Online Power Profiler. And you do not have to add this current, since it is already part of the BLE sleep current.

[alfiero]

ok, thank you! Anyway the I2C transaction event could be "triggered" by an external interrupt or RTC timer

[Stian Røed Hafskjold]

If you want to use an external interrupt to trigger the transaction, make sure that you use the GPIO PORT event to sense the pin. Not the GPIOTE IN event. The IN event will make the chip consume about 20 uA in idle.