High sleep current with SPI reading accelerometer

RE: High sleep current with SPI reading accelerometer

Jason — Wed, 09 Jun 2021 11:56:43 GMT

PPK2 Logic port to the rescue again!

Every time MOSI is left LOW, there's high current in the accelerometer. The AIS2DW12 has an internal pull up which I cannot disable.

This code fixes it

  nrf_drv_spi_uninit(&m_spi);
  nrf_gpio_pin_set(SPI_MOSI_PIN);

RE: High sleep current with SPI reading accelerometer

Jason — Wed, 09 Jun 2021 10:17:17 GMT

I've noticed it was a bit random whether it was high or low so I suspected it was related to the final bit being received from the accelerometer.

If I add a completely unnecessary call to write a byte of zeros to an otherwise unused register on the accelerometer (Z_OFS_USR) then I get almost consistently low sleep current

If I read the WHO_AM_I register then I get high sleep current 100% of the time

Also, if I unplug the accelerometer from the PPK2 and give it power separately then I see consistently low sleep current.

So at the moment, I think this is not nrf52 related. It's the accelerometer somehow.

RE: High sleep current with SPI reading accelerometer

Jason — Tue, 08 Jun 2021 18:56:51 GMT

I've changed to the newer revision NRF52840 Dongle but it's the same power profile.

My method of stopping SPIM1 is to call nrf_drv_spi_uninit(&m_spi) after my last call to nrf_drv_spi_transfer. (after waiting for spi_xfer_done)

Is this the correct method? I cannot see the implementation to check what it does.

When I look in the NRF52840 product spec at 6.25.5 I see this

Should I instead use the ENABLE register?

I assumed that when using the nrf_drv_spi_ calls then I shouldn't need to touch the registers directly.

I tried polling TASK_STOPPED with this code but it was always zero

while (!NRF_SPIM1->EVENTS_STOPPED)     printf ("X");

I also tried setting ENABLE = 0 after calling uninit but it didn't make any difference.

  nrf_drv_spi_uninit(&m_spi);

  NRF_SPIM1->ENABLE = 0;