nrf52 - PPI + EasyDMA Power Consumption

[Jonathan]

A couple of power consumptions Q's for this basic scenario: RTC used via PPI to infrequently sample from ADC and trigger SPI read from external sensor source.

Questions:

• If I'm using PPI to trigger ADC and SPI reads, does the HFCLK need to be enabled the entire time or will/can an event turn on the HFCLK (i.e. should I assume I_HFINT continuous current draw in the system or just when PPI/peripherals other than RTC are triggered)?
• What's the spec'd current consumption for EasyDMA during a SPIM read/write? In other words, is I_SPIM, which is listed at 50uA, just for the SPI peripheral or does that include current consumption for writing to RAM?

Thanks

P.S. Current 51 user. Whiteboarding next-gen theoretical power consumption with nrf52

[Stefan Birnir Sverrisson]

Hi Jonathan

I believe the SPI specification of 50uA current consumption is just for the peripheral itself. The EasyDMA unfortunately is hungry on current and will add around 1.5mA when transmitting data. So in order to save current consumption, set maximum speed for SPI to shorten the time the SPI transmits/receives data.

If you use the SAADC peripheral, you need to again watch out for EasyDMA current consumption. If you have SAADC enabled, it will constantly enable the EasyDMA and current consumption will be >1.5mA. The low power example shown here shows how to use SAADC with low current consumption. Documentation is given in the saadc_low_power/readme.md file