What's the benefit of having an external 32 kHz crystal?

[Guest]

What are the benefits of having an external 32 kHz crystal instead of using the internal RC oscillator?

[davman]

Hello Team Nordic

Is there a similar power-comparison for the new nrf52-series?

/d

[FI]

Just curious Ole, which blocks, especially of the radio, use the 32K?

[energy]

Does this means that we just have to add 10 uA to all scenarios described on the following link to compute the impact of not using external 32khz ?

devzone.nordicsemi.com/.../

Thanks

[vit bernatik]

@CR - I assume that during sleep the 32MHz clock is turned off and 32KHz is turned on. After wakeup the time is recomputed. But due to RC oscilator being less precise - the recomputed time is less precise. So even though HF (32MHz) xtal is started for receiving BLE operation. The RX windows has to be start sooner (in case RC osc was slower) and end later (in case RC osc was faster). Therefore RX windows is wider. And chip has increased RX currrent for longer time - Which no-one wants... If you use small battery and want to run it significantly longer just use 32Khz xtal... Also you will save extra time for calibration. Basically what they most likiely do is that they run precise HF xtal and LF low precise RC. Then they know how many HF clocks is per one LF clcock. And can recompute LF->HF. But the thing is that RC oscilator changes in time due to temperature and what not.

[jjifa]

Is it only about 10uA of current dissipated by not using the 32.768Khz crystal?

I do not want to use crystal, but this should not cause any processor delay.

Current consumption is not a problem for my development.
Of course, we won't use the RTC timer either.
It is just important to make the PCB lighter.
Is it right to remove the 32k crystal in this case?