nRF54L15: high supply current on two boards

[Sreejit]

Two boards with the nRF54L15 (custom design, battery directly on VDD ~3 V, VREGMAIN in DC-DC mode, NCS v3.2.3) draw several mA continuously. Other boards of the same design, running the same firmware, average ~14 µA.

Supply current measured with a PPK2 in source mode (median):

Supply	0.8 V	1.0 V	1.2 V	1.4 V	3.0 V
Normal board	0 µA	0 µA	1 µA	25 µA	39 µA
Board A	1.1 mA	1.5 mA	1.6 mA	1.9 mA	4.4 mA
Board B	3.0 mA	23 mA	49 mA	4.9 mA	8.4 mA

On Board A, all circuitry except the nRF54L15 was removed and the current did not change. After the external DC-DC components were also removed, the current dropped to ~200 µA.

Is this a known issue, and how can we determine the cause?

[ketiljo]

Note that the lowest supply voltage of the nRF54L15 is 1.7 V, see https://docs.nordicsemi.com/r/bundle/ps_nrf54l15/page/chapters/recommended_op_conditions.moonlight/doc/recommended_op_conditions.html

Can you share the schematic and layout of the board please?

How many boards do you see this issue on and what are the total you have tested? It sounds very much as a mechanical issue (short)

[Sreejit]

Hi ketiljo,

Thank you for looking into this so quickly.

You're right about the 1.7 V minimum. We went below it on purpose, to see what each board draws while the nRF54L15 can't run. In that range a normal board draws essentially 0 µA, but the two affected boards still draw a few mA. That's why we think the extra current path is in hardware.

We'd be happy to share the schematic and layout. They're confidential, so would it be possible to continue in a private case?

So far we've seen this on 2 boards out of 10. Both were fitted as spares, and the higher current was there from the first hours of use.

A short is a very fair suspicion and we haven't ruled it out. A visual inspection found no obvious solder problems. On one board, the current stayed high after everything except the nRF54L15 was removed. It returned to normal only once the external DC-DC components were removed. Next we'll check those parts and the area under the QFN for a short, and we'll share what we find.

Thanks again for your help.