JS autoranging issues when in series with Nordic PPK

[thanos_vgenis]

Hi there Matt,

out of curiosity I’d like your take on this:

I was trying to compare Nordic PPK (Power Profiler Kit II) to the JS, so I connected them both in the same circuit.

Tried Power Supply - > JS → PPK → DUT (PPK also needs a ground connection to the PS - lead)

In this case, JS autoranging is messed with by the nordic board, and it seems interesting to know why.

While the JS on its own is just fine:

Something keeps the JS from autoranging correctly, do you have any ideas why this is?

I would assume that the combination of the two devices autoranging would affect them both, yet the Nordic capture seems unaffected.

Nothing pressing as you can understand, just for the sake of knowing.

Many thanks,
Thanos

[mliberty]

I wonder if the JS220 is measuring the PPK’s MOSFET charge injection when the PPK switches current ranges.

It looks like you captured these with the Waveform widget Min/Max set to off. I would love to take a closer look at what is going on. Can you share JLS files? I think they should be small enough to post here, or you can email them to support at joulescope dot com.

[thanos_vgenis]

Yeap, most of the times I do turn ‘min/max’ off, helps me get a better pic of the trace. Maybe if the contrast difference between the actual waveform and min/max was larger it would help, but no issue, it’s just fine as it is.

Here are your captures Unique Download Link | WeTransfer, I did

• power supply → joulescope
• power supply → joulescope → PPK → DUT
• power supply → PPK → joulescope → DUT

I would assume it could be charge injection but I would expect it to be less severe and JS to recover fast.

BR,
thanos

[mliberty]

Thanks for the JLS files @thanos_vgenis . From the PPK II Schematic, it uses a DMP1009UFDF-7 to select each current range. It’s driven by ADA4622-4ACPZ-RL.

The DMP1009UFDF-7 has 26 nC typical gate charge at 4.5 V gate voltage.

One thing you can do to improve JS220 accuracy for lower current systems is to set the maximum current range. In this case, you can likely set either 180 mA or 18 mA, liike this:

Can you try collecting one more scenario in the " * power supply → joulescope → PPK → DUT" setup? Can you set your JS220 to a fixed 18 mA range? If that saturates (the signal goes to 18.5 mA or higher), and you use the 180 mA range instead? This eliminates the JS220 autoranging from the equation to just see the PPK2 effects.

---

I set up a test to see what we should expect.

TLDR; this little test did not help gain any insight.

I configure the JS220 EVK1 like this:

evk.stop()
evk.off()
evk.power_ldo(1.0)
evk.pio_start_sequence(10_000, [[10, 100], [10, 1_000_000]])

Here is a waveform with the JS220 set to a fixed 18 mA range:

I then connect the PPK2 in Ammeter mode between the JS220.Current - and the EVK1 I-.

I do not see the PPK2 charge injection that I was expecting, but the signal is very noisy. It’s noisy enough to prevent the JS220 from autoranging when I set the JS220 back to auto. I have the JS220, EVK1 and PPK2 all connected to the same powered Anker USB Hub.

The next step is to figure out where the noise is coming from and reduce it. Unfortunately, I’m out of time for now

[mliberty]

I increased the EVK1 voltage from 1.0 V to 3.3 V, which also increases current by a factor of three. I now see some pretty significant PPK2 charge injection artifacts that are larger than the noise.

I configured the JS220 for fixed 180 mA current range to completely eliminate any JS220 switching artifacts. We are only looking at the load and PPK2.

EVK1 supply → JS220 → EVK1 load:

EVK1 supply → JS220 → PPK2 → EVK1 load:

My conclusion is that the JS220 is measuring the real PPK2 charge injection current, which causes the JS220 to autorange more frequently than when the PPK2 is not present.