nRF51422 startup time for 32kHz

[takin]

Hello I have a question for startup time for 32kHz of nRF51422. nRF51422_PS v3.1 indicates startup time for 32kHz typ 0.3sec.

What is this spec minimum value. I’d like to know approximately value of this spec.

[Håkon Alseth]

This is unique for each type of external crystal, depending on what physical parameters this crystal has. You'll have to measure it with your chosen 32.768 kHz crystal.

Cheers, Håkon

[takin]

Hi Håkon

Thank you for your answer. If I use the crystal that startup time is 80msec, is that OK for nRF51422 ?

And would you tell me what "tstart,x32k" is meant. I think that it means if startup time of the crystal what I choose below the value, it works with no problem.

regards

[Håkon Alseth]

The parameter tstart,x32k is an example-startup time for a external 32k crystal. What is important when choosing an external 32k crystal is that you are within the maximum parameters specified in chapter 8.1.5. (CL,X32k / C0,X32k / RS,X32k)

[takin]

I think that CPU normally waits for clock stabilization, it's not for 32kHz clock? It's for the only 32M/16M Hz?

It's not necessary to consider the stabilization time of 32 kHz?

[Håkon Alseth]

You'll have to wait until the xosc32k is stable, which is the parameter tstart,x32k. This will be in the range of up to 1 second, depending on what type of extern 32k xtal you choose.