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?

[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. 

[Stian Røed Hafskjold]

KilianL I think I know the problem now. In your original question I see that you wrote "soldered the SB32 in the DK". This is connecting VDD to the SWD external voltage sense pin. This pin is sensing the voltage on the PPK, and on the PPK this line is connected to VDD as well. So by soldering SB32, you power the PPK directly from the DK VDD which is 2.8V. So de-solder SB32 and see if that fixes it.

[KilianL]

I already desoldered this bridge. Now I can only establish a connection between DK and PPK in "Reg" position. Otherwise the PPK seems not be be recognized by the DK. That was the initial reason to solder SB32. 

So in Ext. position the PPK is "dead" an the software is not able to launch. 

[Mishka]

I believe in order to make it work you have to supply externally regulated voltage to the External Supply.

[Stian Røed Hafskjold]

If you soldered SB32 there will be a short between the supply on the DK and the external supply. If the voltage difference is high there will flow a lot of current and you will probably break some components.

If the following steps do not work, it sounds to me that some components on the PPK are broken because of the supply short.

• Set the "Power select" switch on the PPK to the "External" position
• Set the "DUT" switch on the PPK to  the"External" position
• Connect SWD cable from DK to PPK
• Connect USB cable to both DK and PPK
• Supply 3V on the "External supply" pin
• Finally, you can open up the PPK software

[KilianL]

I don't know what's different today, but now I can see the exact voltage that I apply to the External supply clamps also at my DUT. The strange thing is, that the PPK seems to get ints energy also from the external supply, 14 mA at 3V? I thought I can put a battery to the external supply and make long term lifetime tests with a battery capacity, but when the PPK is using the same energy that's not possible. 

[Stian Røed Hafskjold]

Yes, I'm afraid that's not possible.