High power consumption when starting external LFCLK

RE: High power consumption when starting external LFCLK

Quax64 — Wed, 28 Jan 2015 00:40:58 GMT

Stefan, in response to your update of 27.1.2015 regarding the use of the RC: Thank you for the suggestion which is definitely an alternative worth being further investigated. Going from 20ppm to 250ppm will increase radio up time though, but it might still pay off in my application.

RE: High power consumption when starting external LFCLK

Quax64 — Mon, 26 Jan 2015 16:52:07 GMT

Thanks for the response. Whether it is a problem clearly depends on the application. In my application the system is in the SYSTEM ON mode for a relatively short period of time (some minutes) and all it does is reporting infrequent button press events. It is long enough to make it worthwhile starting the external LFCLK but short enough to make the power consumption for starting the clock a considerable factor. This somewhat unexpectedly high power consumption won't render the nRF51 completely unusable for my application and won't matter too much for many other applications, I guess, but maybe it could be reduced in future releases of the chip. I also think that it should be mentioned in the Reference Guide or Product Specification. Anyway, thanks for confirming that this cannot be avoided, so I just have to live with it.

RE: High power consumption when starting external LFCLK

Stefan Birnir Sverrisson — Mon, 26 Jan 2015 15:07:51 GMT

I think there is nothing that can be configured to avoid this current consumption. It is automatically handled internally and can not be configured. Usually, you only draw this current once for each reset, so it should usually not be of that big concern.

Update 27.1.2014 There is also the possibility of using the internal LFCLK RC with the

NRF_CLOCK_LFCLKSRC_RC_250_PPM_TEMP_4000MS_CALIBRATION

option , which will add 2-3 uA compared to a 20ppm crystal. I guess it depends on how frequently you need to start the crystal if it would pay off to use the RC instead, see this thread

RE: High power consumption when starting external LFCLK

Quax64 — Mon, 26 Jan 2015 11:40:56 GMT

Any comments?