nRF54L15 high power consumption when VDD is less than ~2.29V

[cyber_v1]

Hello,

We have a custom nRF54L15 board, that, when powered with 1.8V, shows a too high power consumption. 230uA in system on - low power mode, and 12uA in system off mode.

When it's powered with 2.29V or higher, it shows much better numbers of 6uA and 1uA, respectively. The 2.29V is borderline - anything slightly below, and sometimes it starts up with the higher power consumption, sometimes it starts up ok. At around 2.25V maybe, it's quite consistently starts up with the high consumption.

Changing the voltage without the powering the device off and back on again doesn't affect the power consumption. We thought that maybe DC/DC regulator is not getting enabled, but it does (checked the registers, and waveform at DECD with an oscilloscope).

The board is based on the QFAA reference design, and all custom parts have been disconnected while investigating the issue.

Any ideas what may be wrong, or what to check to investigate this issue further?

[cyber_v1]

It seems the reason for the increased power consumption is the low frequency crystal oscillator not starting up at lower supply voltages.

Are there any special requirements for LFXO not listed in the documentation? I've noticed there is a section about choosing the right HFXO but not about LFXO.

We're using the SC-20S 32.768kHz 20PPM 9pF oscillator from Seiko.

[cyber_v1]

Additionally, can Nordic provide the oscillation loop maximum critical transconductance parameter for HFXO and LFXO in the nRF54 family?