Current consumption of the modem inside nRF9160

[WassimZ98]

Hello. I have a DK nRF9160 0.8.2 version. I am sending AT command through UART with an external MCU (STM). I am interested on evaluating power consumption during an UDP packet transmission and on PSM mode. My multimeter shows a consumption of about 485uA in PSM, it is far higher than the 4uA provided on the datasheet. With a research i understoodthat UART consumes that power, but i need it for serial communication with external mcu. So, is there a way to only measure current consumed by the modem and not by the entire SiP nRF9160?

Or, is there a way to disable via software the UART, for example by sending an AT command? 

Thanks in advice

[Martin Lesund]

Hi Wassim,
I assume you are running the Serial LTE Modem on the nRF9160.

To turn OFF the UART you can run the command "AT#XSLEEP=0".

Unfortunately there is a bug in the Zephyr implementation of the UART that affect this sample to leak 23µA. So in PSM mode you should see around 27µA.

(There is ongoing work to fix this, and hopefully it will be introduced in the master branch in the near future)

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To see the numbers in the datasheet I would instead invite you to run another sample. e.g. modify the coap_client sample or just run this simple udp_psm sample

Change the hostname out with e.g. the static IP address to your UDP server. Then you should see the 4µA in PSM mode.

I see that you have the v0.8.2 DK, which has a ~2µA leakage issue if the VDD_IO switch is set to 1v8, so it is recommended to have the VDD_IO switch (it is right next to the power switch) set to 3V when doing power measurements. 

Here you can see the PSM floor current when running the udp_psm sample:

Best regards,
Martin L.

[WassimZ98]

Thank you very much for the answer. I haven't tested it yet, but i have another question. Do i have to solder an 0.5 ohm resistor on R60? 

[Martin Lesund]

If using an Oscilloscope, that is the recommended approach according to the documentation..
If using a power analyzer or a current meter that is not needed.