RE: Help me understanding theorical power consumption of nRF52832

Tim — Mon, 17 Oct 2016 06:01:33 GMT

Hello Stefan, thank you for this great answer and have a nice day !

RE: Help me understanding theorical power consumption of nRF52832

Stefan Birnir Sverrisson — Fri, 14 Oct 2016 16:58:33 GMT

Hi Tim

Your question is totally relevant. Current consumption was not easily estimated on nRF51 and is even more difficult on nRF52 becuase the internal power management is more complex. I'll try to elaborate.

You are correct, the specified number of 3.7mA is the typical current consumption of the CPU when DCDC is enabled and supply power is 3V. You can experiment with this with by running the template_project in the SDK, measuring the current consumption with or without WFE() in the main loop (__WFE() disables the CPU). Adding

NRF_POWER->DCDCEN = 1;

Enables the DCDC.

You are also correct that average current consumption of the CPU is proportional to the utilization of the CPU, i.e. 0.03N + 0.97(sleep current) if CPU utilization is 3%.

For peripherals, you can see the current consumption of those in the electrical specification for each peripheral in the nRF52 product specification. Those numbers are typically given for current consumption of the peripheral only without DCDC enabled. What you need to consider additionally is that 16MHz clock source is needed, usually internal 16MHz HFINT, for most peripherals (all except RTC, LPCOMP I think). There is also current consumption of internal regulators that consume current, but those currents are generally small on the nRF52, and can usually be neglected. The current consumption of the HFINT is specified to 60uA, but that number is underestimated. I see HFINT current consumption typically 200uA-500uA.

Another thing to consider is the EasyDMA, which many peripherals use. EasyDMA consumes typically ~1.5mA when enabled. For example, the SAADC uses EasyDMA and when SAADC is enabled, it consumes ~2mA all the time, which is sum of 16MHz clock source, the SAADC perihperal and the EasyDMA. For SPIM, I understand that the EasyDMA only consumes current when SPI data transfer is ongoing, otherwise not.

Update 18.10.2016 Usually there exist methods to decrease use of EasyDMA and 16MHz clock in order to decrease current consumption. For instance, the saadc_low_power example given here is power optimized so that SAADC is only enabled when sampling to reduce current consumption. The 16MHz clock and the EasyDMA will then only consume current when the SAADC is sampling, for 5 to 42 microseconds, depending on the SAADC acquisition time configuration. Also if you disable UART logging and set SAADC buffer size to 1 in this example, you will see current consumption of only a few microamps for sub 10Hz sampling rate.