Effect on BLE functionality based on LFCLK accuracy

[Anand Ramashetty]

Hi ,

During SOFTDEVICE_HANDLER_INIT function call , if I change the NRF_CLOCK_LFCLKSRC_XTAL_20_PPM macro to NRF_CLOCK_LFCLKSRC_RC_250_PPM_8000MS_CALIBRATION , what is the consequences on BLE functionality . Will it affect complete product feature in the feature , any time related issue will affect? Please provide me details on this.

As i know one thing that if I change it to 250PPM it will decrease the initialization time, but I want to know on the effect on product functionality.

Regards, Anand

[Asbjørn]

The change in LFCLK accuracy will not change the initialization time, but it will make the RX window for your application wider due to less accuracy on the timer. So you will pay with a slightly higher current consumption due to the longer RX window that you have to use in order to ensure that your radio is on for the entire connection event. If you use a 20 ppm 32 kHz crystal, the accuracy is of course better and you can have a shorter RX window and still be within the connection interval.

[Anand Ramashetty]

Hi osfo ,

Thanks for the information. Apart from more energy consumption, we can say that it will not affect the functionality of BLE.

But what will be the affect of calibration time on functionality. The 250 PPM uses 8000MS , but what is the calibration time for NRF_CLOCK_LFCLKSRC_XTAL_20_PPM?

Regards, Anand

[Locky]

There is no calibration when you specify an external crystal. It is up to you to specify the accuracy/tolerance of the crystal which should be in the data sheet for the component you designed with. This is the lowest current consumption setup. Using the RC setup requires constant calibration and wider RX windows, thus much for current consumption overall.