Measure current of nRF52840-DK with a connected secure element via I2C

RE: Measure current of nRF52840-DK with a connected secure element via I2C

Stian Røed Hafskjold — Thu, 20 Feb 2020 11:38:12 GMT

Yes, the USB cable has to be plugged in to power the VDD domain on the DK, this includes the debugger MCU, the IC switches, etc. If they are not powered they will be floating and you get unpredictable behavior, and you will get leakage through the SWD pins.

I tried a Zephyr example now, just putting the k_sleep(1000) in the main loop, and not initializing anything more and I get a current draw of 3 uA on the external supply header. With the same setup as I described below. Without the SE.

RE: Measure current of nRF52840-DK with a connected secure element via I2C

MarDor — Mon, 17 Feb 2020 15:54:37 GMT

The J2 must be pluged in for the measurement, even though when the debugger MCU is not powered?

I took a mseaurement with this setup. Average values were:

During Access of the SE: 20mA
During Zephyr's k_sleep(): 7mA
Complete Average: 8mA

Are there any experience on your side of power consumption during Zephyr k_sleep() on the nRF52840-DK?

RE: Measure current of nRF52840-DK with a connected secure element via I2C

Stian Røed Hafskjold — Mon, 17 Feb 2020 15:26:21 GMT

Ok, let me know how it goes. That is correct.

RE: Measure current of nRF52840-DK with a connected secure element via I2C

MarDor — Mon, 17 Feb 2020 15:07:15 GMT

Thanks, for your support. I will try it with this setup.
If SB40 is not cut I do not need any additional jumper right?

RE: Measure current of nRF52840-DK with a connected secure element via I2C

Stian Røed Hafskjold — Mon, 17 Feb 2020 14:57:08 GMT

Hi, not sure if that's going to work. You need to set the SW10 to "ON" in order to isolate the debugger MCU from the nRF chip. Then the USB cable will have to be plugged in to power the debugger MCU, and the P21 will power only the nRF chip. But, If you use the Arduino headers for the Infineon board, it will be powered from the same domain as the debugger MCU on the DK, which is now powered from the USB, and thus measurements on P21 will not include the infineon board.

If you leave SW10 in the "OFF" position, you will measure the whole setup including the debugger MCU which will add several mA to the measurements.

I think the only solution is to remove the Infineon board from the Arduino headers, and do the wiring manually. Here's what you can try:

Power analyzer connected to P21
SW10 -> ON
SW9 -> VDD
SW6 -> nRF only
J2 plugged in
Add jumper to P22 if SB40 was previously cut
Connect VDD_nRF on P20 to VDD on Infineon board
Connect GND from DK to Infineon
Connect I2C wires from DK to Infineon