nrf52840 System Idle Current Too High

[Mark J]

Hi,

My firmware is working well and handling required functions, so I have begun trying to work on power management to reduce device power draw. I am using S140 and my BLE peripheral is sending a proprietary advertising packet every second. When not advertising, it is idle but checks counters within a 100 mSec timer handler.

I have introduced a 6.8 ohm resistor between the positive post on my battery and VDDSOC (positive power) on my custom board. Measured mV or uV across this resistor gives me current. When idle, I am measuring 1 mW (approx 160 uA). I am expecting < 5 uA when idle.

I have confirmed that BLE functions are not the culprit as this measurement is unchanged regardless of whether I measure it between advertising periods or when advertising is disabled.

I also use SPI to talk to an accelerometer, but I have confirmed that SPI is not the issue as current is unchanged if I don't enable SPI. 

No other peripherals such as UART are used.

I have disabled NRF Logging (#define NRF_LOG_ENABLED 0 and #define NRF_LOG_DEFAULT_LEVEL  0 in sdk_config.h).

I am using Seggar_RTT logging, but I have unplugged my JLink interface when measuring power and I understand that Seggar_RTT logging is dormant and does not use power when there is no JLink connection to a target.

I am using LFXO with the following config.

#define NRF_SDH_CLOCK_LF_SRC NRF_CLOCK_LF_SRC_XTAL

#define NRF_SDH_CLOCK_LF_RC_CTIV 0

#define NRF_SDH_CLOCK_LF_RC_TEMP_CTIV 0

#define NRF_SDH_CLOCK_LF_ACCURACY NRF_CLOCK_LF_ACCURACY_20_PPM

I have a single app timer set at 100 mSec. I have confirmed that it is not contributing to much draw as the current does not change when I disable the functions handled within it.

In previous projects (e.g. nrf52832) I was able to get the idle current down to a few uA by setting: sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE); and using preprocessor directive SWI_DISABLE0 ... but I am already using these and I am still over 150 uA.

I have spent a lot of time confirming that peripherals are not active and they should not be contributing to any significant draw (LED controller is disabled and my acc is being put to sleep via SPI).

My startup code is below. 

int main(void)
{
  ret_code_t err_code;

  // Initialize logging through Nordic and terminal.
  SEGGER_RTT_Init();

  SEGGER_RTT_printf(0, "Logging started.\n");

  // As per egs, setup the clock driver to use the lfclk (before timers_init)
  APP_ERROR_CHECK(nrf_drv_clock_init());
  nrf_drv_clock_lfclk_request(NULL);

  APP_SCHED_INIT(SCHED_MAX_EVENT_DATA_SIZE, SCHED_QUEUE_SIZE);

  // Init the bmi160 connection (includes spi master).
  xtag_init_bmi160();

  // Ensure that it is powered down for now. Woken upon config.
  xtag_suspend_bmi160();

  // Init timers.
  timers_init();

  // Init buttons and LEDs.
  gpio_init();

  // Init power managment.
  APP_ERROR_CHECK( nrf_pwr_mgmt_init());

  // Init BLE elements.
  ble_stack_init();
  gap_params_init();
  gatt_init();
  xtag_adv_config(true);
  services_init();
  conn_params_init();
  //peer_manager_init();

  // Start advertising.
  xtag_adv_start();

  // Start the 100 msec timer.
  err_code = app_timer_start(m_100_msec_timer_id, APP_TIMER_TICKS(100), NULL);
  APP_ERROR_CHECK(err_code);

  // Enable DCDC mode (low power support in idle mode).
  err_code = sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE);
  APP_ERROR_CHECK(err_code);

  // Enter main loop.
  for (;;)
  {
    nrf_pwr_mgmt_run(); 
    app_sched_execute();
  }
}

Any other suggestions for changes would be appreciated.

Thanks in advance.

Mark J

[Kenneth]

You may check out this in general:
https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/optimizing-power-on-nrf52-designs

You may also check if there is any floating GPIO's and/or internal pull-ups enabled that is is pulled-low etc.

[Mark J]

Hi Kenneth,

I had reviewed the page that you linked and I have followed all recommendations in that link.

We only have 2 other GPIOs that are floating and may be contributing to some extra current, but my hardware engineer suggests that this contribution will be < 10 uA.

Is there any way for another peripheral to use current - even if I have not initialized it? My source code is derived from another Nordic example - Heart Rate Service under ble/peripheral. This source included many software components and peripherals that I am not using (e.g. peer_manager.h, nrfx_uart.h, etc). Even if I do not initialize these elements - is there any way for them to contribute to a current draw when compiled into a project? I cannot imagine how, but thought that I would ask.

Perhaps another approach is for me to re-create my SES project using an example that demonstrates low power "out of the box"? I can slowly introduce my required elements (e.g. SPI Master) to this example and monitor power at each step. Is there such an example?

Thanks in advance.

Mark J

[Kenneth]

I believe most BLE peripheral have low idle current as long as LEDs and UART (logging) is not enabled. What version of the nRF52840 DK kit are you using?

Floating input pins can draw excessive current of several hundreds of uA if not connected to logic level.

[Mark J]

Understood on the BLE peripheral examples. I will assume that the example that I used as a template is ok (from a low power perspective).

I had tried adding the following code - in an effort to get the power down:

err_code = sd_power_mode_set(NRF_POWER_MODE_LOWPWR);
APP_ERROR_CHECK(err_code);

Should that be put within init code (within main.c) to ensure low power mode? If it is there - I suppose it cannot hurt. Please confirm. Note that this code is not in the Nordic examples that I have seen, so I assume that it is not required, but I would like to confirm.

I will work with my hardware engineer to enable a pullup or pulldown as required on all inputs and outputs.

Thanks,

Mark J

[Kenneth]

Default mode is low power yes. 

Kenneth

[Mark J]

I setup GPIO as requried and then found that the issue was actually related to my incorrect sleep of the accelerometer. Left the floating GPIO inputs init as input with pullup as this is good practice from what I have read online.

Down to approx 10 uA and most of that is for a sleeping accelerometer.

Tx for the help.

Mark J