power consumption is too high on my nrf52 SoC

[Juliusc]

Hi, 

I am currently trying to decrease my power output, for this purpose I used a power profiler and found this pattern:

I am using a test firmware that just disables all unused gpio ports, start ble and then goes into while(1){ __WFE();}

power consumption is never below 400uA, the spikes seem fine (BLE advertising spikes I presume).

s there anything you can tell me about why this would happen?

Even if I turn of BLE I still got 200uA on average, so some of the problem is probably in my configuration (but. already increased the adv intervals) and part of it is the chip by itself. I am using a custom PCB but am pulling down all GPIO ports

Best, Julius

[Vidar Berg]

Hi Julius,

Unused pins can be left floating without affecting the sleep current as GPIO pins are configured as inputs with the input buffer disconnect after reset. 

Are you developing with the nRF Connect SDK or the nRF5 SDK? 

Best regards,

Vidar

[Juliusc]

nRF5 SDK

I see I noticed that the current is a bit higher when I dont set certain gpio pins to clear specifically. 

[Juliusc]

I actually noticed something while investigating, I used the following lines in my ble setup: 

  NRF_CLOCK->TASKS_HFCLKSTART  = 1;
  while ( NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);    

and when commenting them , the average went down significantly (at least on the DK, I will test this on my custom PCB later). Though I think I included this because there was a problem with the SD but I cannot pinpoint what exactly it was. What are your thoughts on this?

[Juliusc]

still it looks like something is requesting air time every ms, the advertising event only occurs every 500ms as defined, thats whats so weird

[Vidar Berg]

Writing '1' to NRF_CLOCK->TASKS_HFCLKSTART will start the 32 MHz crystal oscillator, and the crystal oscillator is not automatically released in sleep. The run current with the oscillator active is about 200 uA. 

[Juliusc]

ok thanks so I will leave this out and I also found out that my saadc sampling is responsible for most of the drainage besides that. 

[Juliusc]

what do I need to do in this function to decrease the power consumption:

void saadc_sampling_event_init(void)
{
    ret_code_t err_code;

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
    err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);
    APP_ERROR_CHECK(err_code);

    /* setup m_timer for compare event every 400ms */
    uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_timer, 400);
    nrf_drv_timer_extended_compare(&m_timer,
                                   NRF_TIMER_CC_CHANNEL0,
                                   ticks,
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
    nrf_drv_timer_enable(&m_timer);

    uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,
                                                                                NRF_TIMER_CC_CHANNEL0);
    uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();

    /* setup ppi channel so that timer compare event is triggering sample task in SAADC */
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
                                          timer_compare_event_addr,
                                          saadc_sample_task_addr);
    APP_ERROR_CHECK(err_code);
}

[Vidar Berg]

You need to change the way you trigger SAADC sampling if you want to reduce the sleep current. The typ. system current with a TIMER instance running in System ON is around 500 uA (see TIMER running). I would recommend just using the app timer and trigger sampling from a timer callback. 

[Juliusc]

alright, thanks so much for your help you provided very valuable input!