RE: Power consumption reading a large fifo - Easydma list vs Cpu reading

ShannonPahl — Mon, 16 Oct 2017 17:19:03 GMT

excellent, thanks. #2 is the reason as I have the sensor on a breadboard connected to a DK. When I drop SPI down from 8M to 125K, the current drops from 3.9mA to 1.57mA during a (now longer) read. A pcb should fix this.

RE: Power consumption reading a large fifo - Easydma list vs Cpu reading

MartinBL — Mon, 16 Oct 2017 10:37:42 GMT

Hi,

This is most likely caused by two reasons:

The DMA logic draws 1.2mA alone.
Pin and trace capacitance combined with high frequency signals draw more current.

The current consumption caused by issue #2 is difficult to estimate, but at least you can figure out whether this is indeed the problem by reducing the frequency and see if the current goes down.

It should be safe to assume that at least the CPU is in sleep mode since otherwise the current consumption would be even higher (CPU + DMA run currents would be ~4.9mA at best).

EDIT: Relevant post with relevant equation. With this equation in mind you would need a relatively high capacitance to reach the mA range. The nRF52832's pad capacitance is only ~3pF, but if you have connected your SPI slave with jumper wires, the capacitance quickly adds up.