Voltage at PPK without external supply

[KilianL]

We have our first prototype ready and were measuring the power consumption. During development the values seems to be wrong.

So I just added a voltmeter to the DUT out clamps and put the switch into external position. Surprisingly I measured 2,28 V. How could that be? No external supply was present? Even when I put a 3 V supply to the "External supply" I measured 2,28V? Where does this voltage come from? In my opinion there should be noting?

The second try was to disconnect the DK from the PPK. I connected the two board with a 10pin flat cable, soldered the SB32 on the DK to switch to the external device, and supplied 3,2V from external. The output of "External DUT" was always 2,8V. 

Thanks for your help.

[Stian Røed Hafskjold]

Hi, you need to run the PPK software at the same time as you are measuring the voltage. The PPK software is configuring the PPK correctly.

The voltage on the DK is 2.8V because of the reverse voltage protection diodes on the DK. So in DK mode, you should see 2.8V on the DUT output.

The external regulator is not working properly when the PPK is stacked on top of the DK. Use it in standalone mode as you are showing in your first picture. This setup should work properly once you start the PPK software.

[KilianL]

Hi, the PPK Software is running and the boards are separated. With or without a second usb cable on the PPK I can not apply voltage below 2,8 V. Something is back powering to the "External supply" clamps. Any other bridges that I can cut to have just the raw external voltage for my DUT?

[Stian Røed Hafskjold]

When measuring the voltage, do you apply any load to the DUT pins, or are they floating? Which PPK revision is this?

[Stian Røed Hafskjold]

And which software version are you using?

[Mishka]

This perfectly explains my case - I connected the PPK on top of the DK. After moving it out of the DK it started to work properly (1.8 - 3.6V external supply is required though). Thank you!

BTW, my PPK revision is 1.1.0, model PCA63511, dated 2018.26. Software: 2.3.1 (macOS nRF Connect 3.3.0). I also found it's very important to update PPK firmware as well - it fixed strange things for me couple of times. Simply erase it with nrfjprog and reconnect.

[KilianL]

I'm using PPK Rev. 1.1.0, PK Software 2.3.1 and the Firmware of PPK I just erased and flashed with the latest firmware. My issue remains, the PPK is back powering my external power supply with 2,85V. I can switch the DUT on and off with the software but External or Reg is powering the DUT always with 2,7 V or above. Lower is not possible.