SYSTEMON vs SYSTEMOFF sleep

[Nikollao]

I was reading the Errata document for the NRF54L15, and came across this: 3.18 [37] POWER: Current consumption might increase after pin reset or power cycle. So I was wondering as a rule of thumb, what time interval is SYSTEMOFF sleep more power efficient than idle sleep (WFI)? Is it eg for anything above 1 second preffer system OFF, or something like that? 

[Vidar Berg]

Hello,

Waking up from System OFF will trigger a System Reset, so even though you could likely achieve a lower average current for longer intervals, it’s not a viable option for most types of applications to enter system OFF periodically.

Best regards,

Vidar

[Nikollao]

If I have a period eg record data 1 every hour it would make sense to use systemoff. My question is, power-wise what period would systemoff make sense compared to wfi? 1 second, 5 seconds, 1 minute? 

[Vidar Berg]

Yes, that would make sense if you’re going to record data once every hour and don’t need any BLE connectivity in between. The cost of wakeup will depend on your application  boot validation mechanisms in the bootloader, scatterloading, driver initialization, etc). I'm afraid my best suggestion is to profile this with your FW and HW.

[Nikollao]

Does Nordic provide any information how much energy the NRF54L15 uses during power up etc? 

[Vidar Berg]

We specify the system run current with the CPU active, the startup time before the first instruction is executed on wake-up, etc. in the datasheet, but this alone isn't sufficient to make any estimates how much energy your device will consume as we don't know what the FW needs to do on startup before it's ready to perform tasks (record data for example). It's best to measure the startup current using a PPK2 or similar. 

[Nikollao]

Thanks.