Torelance for Synthesized Clock 32768kHz

[kaku]

Hello, Everyone:) Nice to meet you !

Please could you commennt my first question on this community zone. I've a question for the accuracy of synthesized clodk 32k on nRF51822.

1st, I think, the synthesized clock(32k) would be devided by some ration for HFCLK(RC16MHz or X'tal 16MHz), internal nRF51822. Could you tell me the "divided ratio" ? It's probably imbossible to get the just precise value"32.768"kHz from HFCLK(16Mhz).

2nd, On the the latest datashhet nRF51822 Ver2.0, the tolerance for synthesized clock(32k) is X'tal 16Mhz +/- 8ppm. Also X'tal 16Mhz also has a torelance +/- 50ppm. So, the synthesized clock for tolerance is 32khz(maybe 32.766...) +/- 58ppm. Am I correct ?

Because I want to know the accuracy of synthesized clock(32k) if this synthesized clock can use RTC etc.

Thanks Best ergards, Izumix

[Ole Morten]

Synthesizing the low-frequency clock from the 16 MHz should work, and should give fairly high precision, but it is not something I'd recommend simply due to current consumption.

Having the 16 MHz enabled will consume ~1 mA current, and when synthesizing the LFCLK from the HFCLK, this current will always be drawn, essentially making any low-power application impossible.

Edit: Take a look at this question for an overview over the possible LFCLK sources.