nRF52 LFSYNT tolerance

RE: nRF52 LFSYNT tolerance

Petter Myhre — Sat, 07 Jan 2017 16:10:09 GMT

I don't think it is possible to get 20 ppm with synth, and again you shouldn't use it. From the S132 v3.0.0 release notes:

Synthesized low frequency clock source is not tested or intended for use with the BLE stack.

RE: nRF52 LFSYNT tolerance

Borkis — Sat, 07 Jan 2017 15:27:27 GMT

Thank for you answer, Peter.

I understand it will draw more current but in central role system I have access to mains power, so the current consumption increase can be tolerated
Unfortunately your explanation does not answer my question (RC synth is still 250ppm). Let me rephrase to be more specific: How to force the tolerance of the low frequency clock in the absence of 32kHz xtal in central role so that during connection request the sleep clock accuracy is reported as 20ppm?

RE: nRF52 LFSYNT tolerance

Petter Myhre — Thu, 29 Dec 2016 11:13:41 GMT

In general NRF_CLOCK_LF_SRC_SYNTH is not recommended, because it will keep the HFCLK running, drawing more current compared to the RC. If you don't have an external 32 kHz crystal, it is recommended to use NRF_CLOCK_LF_SRC_RC with the configuration in the migration document:

// Recommended configuration for using the RC oscillator with s132 (see nrf_sdm.h
for details)

nrf_clock_lf_cfg_t rc_cfg = {
    .source = NRF_CLOCK_LF_SRC_RC,
    .rc_ctiv = 16, // Check temperature every 4 seconds
    .rc_temp_ctiv = 2, // Calibrate at least every 8 seconds even if the temperature hasn't changed
};