possible to shutdown soft device or BLE after init to achieve low power?

[Brian]

Hey guys,

With the BLE stack initialized, I’m not able to get the power down to where I’d expect with nRF51822, running SD S110 8.0 and SDK 9-2.

I’ve tried three, very basic tests, with current measured at the battery. See test code below, where I try disabling the soft device in an attempt to achieve the same low power before I initialized the BLE stack.

Note: the BLE stack is getting initialized with the RC clock synthesized from the HF crystal. No 32KHz crystal in HW. Could this be the source of the 418uA draw versus the 2.2uA? SOFTDEVICE_HANDLER_INIT(NRF_CLOCK_LFCLKSRC_SYNTH_250_PPM, NULL);

Is there a way to shutdown the BLE stack or SD to get the current down to the 2.2uA example code below?

Thanks! Brian

//2.2uA
main() {
  while(1) __WFE(); 
}

//418uA
main() {
  ble_stack_init();
  while(1) sd_app_evt_wait();
}

//418uA
main() {
  ble_stack_init();
  nrf_delay_ms(100);
  softdevice_handler_sd_disable();
  sd_softdevice_disable();
  while(1) __WFE(); 
}

[Ole Bauck]

You are using synthesized LFCLK. This requires the HFCLK to be running. To get 250ppm accuracy, the HFCLK must be generated from the HFCLK crystal oscillator. I tested and get around 300uA.

I suggest you use NRF_CLOCK_LFCLKSRC_RC_250_PPM_4000MS_CALIBRATION instead.

[Brian]

Thanks Ole! Understood. But, shouldn't we be able to turn off the soft device, after we have initialized it so that we shutdown the clock all together and get back to ~2.2uA as measured before we initialized BLE?

...by calling these functions? softdevice_handler_sd_disable(); sd_softdevice_disable();

[Ole Bauck]

The SoftDevice does not stop the LFCLK when it disables because other modules may use it (like app_timer). To stop the LFCLK add this line of code (after softdevice is disabled):

NRF_CLOCK->TASKS_LFCLKSTOP = 1;

[Ole Bauck]

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