Current consumption increase when using SPI on lower power domain

[wgeeurickx]

Hi,

I'm developing an application with an nRF54L15 on a custom PCB and I'm looking to minimize the current consumption. The application is very simple, just a sensor that is connected over SPI and read out every X ms when data is available. In my previous revision of the PCB, I wasn't fully aware of the constraints of the nRF54L15 compared to the nRF52 series (I routed an interrupt pin to a GPIO from P2, which doesn't have GPIOTE) and I didn't specifically design around power domains. That's how I ended up using SPI00 with pins on P2 (following nRF54L15DK). Thinking that I could save on current consumption by using SPI22 with P1 instead, I had a new revision of the PCB made with the interrupt pin correctly routed to a P1 pin. 

Upon testing, though, I noticed a higher current consumption using SPI22 compared to SPI00. Is this to be expected?

Current consumption with SPI00

Current consumption with SPI22:

It seems that with SPI22 something is powering on for some short time, consuming more current than is the case with SPI00. 

[Edvin]

Ok. I got to test this now. What I see is that SPIM22 is better than SPIM00 when using pins on P1. This is because the SPIM22 belongs to the peripherall domain (power domain), while the SPIM00 belongs to the high speed domain. The peripheral domain also "owns" the pins on P1. 

So:

P1: Belongs to peripheral domain
SPIM22: belongs to peripheral domain
SPIM00: Belongs to high speed domain.

Whenever a peripheral on one domain uses pins on a port that belongs to a different domain, both of the domains needs to be powered. In addition, the pins needs to be forwarded to this other domain, which also draws a bit more current.

You can read a bit about the power domains here:

https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/overview.html#ariaid-title2

Best regards,

Edvin