The current peak of 334uA during system on Low power mode

[Surya]

I observed a peak of 334 ua during system-on low-power mode during idle time which is periodic around 4 sec. I am using ble with RC clock option.

1.is it waking for calibration of the clock source?

2.how much current will be drawn for calibration of the clock?

3.how to stop calibration for a time period where ble is not used?

[Turbo J]

RC calibration wakes just the HF crystal clock for a while in order to sync the clocks.

If you really care about idle power consumtion, just populate the LF XAL and use the crystal LF clock.

[Surya]

hi, thanks for your reply.

can I know how much current is drawn during calibration?

do you mean to say it is not possible to stop calibration even when I am not using ble?

to do so there is no other way than going for a xtal crystal?

[Simonr]

Hi

As Turbo J says, the LF XTAL will reduce the overall current consumption significantly to any of the other LF clock options. You can check out the Online Power Profiler for BLE to see the differences between idle currents in a variety of configurations.

If you set the device to "system OFF" mode, the LF clock won't have to run, and the current consumption will be more similar for both instances, but in system ON mode an LF clock will be running, and if using the RC oscillator, it will have to wake up from time to time to recalibrate.

Best regards,

Simon

[Surya]

hi Simonr, thanks for your reply.

as you can see my question is about if RC calibration is causing the current how to stop calibration. I don't want to change the clock option as I can't change the hardware now. 

• I want to know  "how much current will be drawn for calibration of the clock?"  if this is a known number.
• I am seeing these peeks when I initialized and stopped the BLE which should not happen. is it like if once i configure i can't stop calibration?

[Simonr]

Hi

The RC oscillator calibration can be adjusted by tweaking the calibration timer interval and calibration timer interval under constant temperature (NRF_SDH_CLOCK_LF_RC_CTIV and NRF_SDH_CLOCK_LF_RC_TEMP_CTIV in sdk_config.h). The SoftDevice should only wake up when it needs to calibrate the LFRC clock, but keep in mind that setting higher values than the recommended 16 and 2 (at least every 8 seconds within temperatures of 0.5°C and every 4 seconds if the temperature is changing) will most likely cause the oscillator to drift. Not calibrating the LFRC will likely lead to inaccurate timers in the low power mode for instance.

When the SoftDevice wakes up, the current peak will increase quite a bit, but the average current consumption during sleep when using the LFRC should not be much more than ~0.4µA according to the Electrical specification in the PS (see ION_RAMOFF_RTC versus ION_RAMOFF_RTC_LFXO for instance).

Best regards,

Simon