NRF52840 power consumption

[mgux]

Hi,

I am trying to minimize the power consumption on a NRF52840.

https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/optimizing-power-on-nrf52-designs states that the power consumption in SYSTEM_OFF should be some nA.

My system consists of a NRF52840 (with Softdevice S140, SDK 17.0.2) and a SPI slave device with a low active reset pin.

I started at 0.7mA for my whole system if the NRF52840 is in SYSTEM_OFF and the slave in reset, that's way to much.

First I noticed, that

void nrf_drv_spi_uninit(nrf_drv_spi_t const * p_instance)

does not reset all used pins but only MISO. I set them all back to default

nrf_drv_spi_uninit(&inst);

nrf_gpio_cfg_default(pin_ss);
nrf_gpio_cfg_default(pin_miso);
nrf_gpio_cfg_default(pin_mosi);
nrf_gpio_cfg_default(pin_sck);

and reduced my power consumption to 0.44mA.

Is this uninitialization by purpose?

Furthermore I could reduce the power consumption to 0.014 mA if I disconnect the SPI slave from power.

Even an empty main like

int main()
{
    nrf_pwr_mgmt_shutdown(NRF_PWR_MGMT_SHUTDOWN_GOTO_SYSOFF);
}

draws 0.011mA.

Any hints where I can search to reduce the power some more?

A simple main like

#include <nrf_log.h>
#include <nrf_log_ctrl.h>
#include <nrf_log_default_backends.h>
#include <nrf_pwr_mgmt.h>
int main()
{
    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();
    while(1)
    {
        if(NRF_LOG_PROCESS() == false)
        {
            nrf_pwr_mgmt_run();
        }
        NRF_LOG_INFO("wakeup");
        NRF_LOG_FLUSH();
    }
}

does not idle in nrf_pwr_mgmt_run(). Could be there anything wrong in my sdk config?

Best regards

Matthias

[Amanda Hsieh]

Hi Matthias, 

In system OFF the whole chip is shut down, so it doesn't matter how the code looks like. The chip itself does not draw more than about 300 nA in system OFF, so there must be some other leakage currents with other external components. 

Regards,
Amanda