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Voltage measurements on custom PCB while PPK is connected

A.P

Hi!

I'm trying to measure the voltage drop across a custom PCB we're developing. This was done while trying to get a clear sense of the current consumption used by our board, using a PPK on top of a DK, with a setup similar to the one described in figure 2 here.
What we find is that we measure a ~2.1V drop across our PCB, while connecting a DMM in parallel to the PCB, not the 'expected' 3V from the battery.

Reading a post here on dev zone, which referenced this article on the affects connecting a voltmeter has on the  measured circuit, I believe our measurements are sound, but I wanted to run this by smarter people.

So, using the resistance measurement option in our DMM, we measured ~4M Ohm on our PCB between VDD and GND, and ~1.5M Ohm between the two pins of the external DUT connector (P16) on the PPK, to get the equivalent resistance of the DK+PPK. I'm not sure how accurate this method is. We are also assuming a ~10MOhm resistance to our voltmeter.

Using the above figures, and assuming the PPK+DK equivalent load is sequential to our parallel voltmeter+PCB load, we get an expected voltage drop of about ~2V across our PCB.

My questions are:
1. Is an equivalent resistance of ~1.5M Ohm to the PPK + DK sound reasonable?

2. Is our assumption that the PPK is in sequence with the PCB correct for the described connection?

3. Is the 2V reading on our PCB nothing to be concerned about, as we suspect?

Thanks!

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  • 0
    1. Not at all. The impedance of the PCB with respect to the source varies continuously, from a few hundred ohms to Mohms depending on it's current load. 

    2. I'm afraid not. The PPK is the source. 


    What is it that you're trying to achieve with these calculations, what is your actual issue?


  • 0 in reply to haakonsh

    Hi!
    Thanks for answering so quickly!

    We're trying to understand the current measurements the PPK is giving us. To be more specific, as we understand it, the PPK measures the current across our PCB, but we are not sure at what voltage, and when we try to measure the voltage across our PCB by connecting a voltmeter in parallel with it, we get values of ~2V, which is not the ~3V we expect.

    We've tried using the DK regulator as the power supply, as well as connecting an external DC supply as detailed here.
    With the DK regulator as the power supply, we tried changing the Voltage Regulator scroll bar in the Power profiler but we don't measure the value we set in the scrollbar over our PCB.

    With an external DC source, the scrollbar value seems to have little to no affect on our measurements.

    How can we ensure the voltage input into the PCB is ~3V, or any other value for that matter?

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  • 0 in reply to haakonsh

    Hi!
    Thanks for answering so quickly!

    We're trying to understand the current measurements the PPK is giving us. To be more specific, as we understand it, the PPK measures the current across our PCB, but we are not sure at what voltage, and when we try to measure the voltage across our PCB by connecting a voltmeter in parallel with it, we get values of ~2V, which is not the ~3V we expect.

    We've tried using the DK regulator as the power supply, as well as connecting an external DC supply as detailed here.
    With the DK regulator as the power supply, we tried changing the Voltage Regulator scroll bar in the Power profiler but we don't measure the value we set in the scrollbar over our PCB.

    With an external DC source, the scrollbar value seems to have little to no affect on our measurements.

    How can we ensure the voltage input into the PCB is ~3V, or any other value for that matter?

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