nRF9160 Feather Drop in Efficiency @ >4V VBAT

ceng

Hi, has there been any investigation into what component is causing excessive power consumption when the VBAT supply voltage is greater than 4V? The buck design is one of the examples from the TPS62840 with efficiency graphs given, and it shows no such drop off in efficiency for higher supply voltages.

I saw that 4.0V is the minimum operating voltage for the V_REGIN input of the CP2102, perhaps that somehow starts leaching power from somewhere when VBAT is >4V?

jaredwolff

Hey ceng

I am in the process of debugging it. It’s definitely something in-circuit as the TI EVK does not exhibit this issue. Without the TI part though I can sweep the input voltage without issue.

I’m hoping to have a solution soon. Stay tuned.

jaredwolff

@ceng found the issue. Unfortunately it won’t get addressed until the next spin of boards. (It requires a PCB change)

ceng

Thanks for the update, do you mind sharing what the issue is? If it is something I can fix on my v5 boards with a mod then I would prefer to do that in the meantime.

AchimKraus

Is that related to Quiescent current seems to depend on VBAT (v5)?

jaredwolff

@AchimKraus same problem. The fix does fix the higher current at higher voltage. It does require cutting a trace and running a short wire.

If that sounds manageable to you guys I’ll try to rework a board and take a good picture.

ceng

jaredwolff A picture with the modification carried out would be much appreciated thank you

AchimKraus

same problem

Thanks!
Though my devices run from battery, that situation last only very short, so it’s not really an issue.

ceng

Or even just a description of the modification is fine for me. Is there a rough timeline yet for when there will be a HW revision that incorporates the fix? I’d like to order more of these boards for use in projects but if I can hold off a bit longer and wait until a HW revision so I don’t have to mod more than necessary myself, this would be preferable.

jaredwolff

@ceng it won’t be until late Q1 at the earliest.

If you’re using the RTC, the trace on U8.10 going to VSYS should be cut. I use an exacto knife (carefully!). Then the RTC side should be connected to +3V3. The easiest way is to connect the +3V3 side of C17 to the same on C21.
If you’re not using the RTC, you can remove U8 all together with hot air.

Here’s a picture of a hasty rework.

AchimKraus

the trace on U8.10 going to VSYS should be cut

That’s the trace, which a tiny part goes to C17 (below your blue wire)?

jaredwolff

AchimKraus Yea you can’t really see it. Here’s the cut