Custom nRF52 board partially start

RE: Custom nRF52 board partially start

Fabien Comte — Mon, 29 Feb 2016 20:37:35 GMT

It was not to test accuracy but just if it works (a kind of prototype production selftest). I modified my 10 pF to 12 pF as recommanded by Nordic and it works fine. Thank you for your help.

RE: Custom nRF52 board partially start

run_ar — Mon, 29 Feb 2016 13:24:34 GMT

The 16M RCOSC is not accurate enough (typ 1%, max 5%) to test the accuracy of the 32KHz clock.

Not sure why it doesn't work with the 32 KHz crystal oscillator, but I would guess the startup time is to long with the current load capacitor, or that the crystal is not soldered properly. 18 pf could be just as bad as 10, but you try. The best thing would be if you can find 14 pf. Regardless, if you cannot load the crystal properly (cannot find the correct size), you will probably be better of just running on the RC (loading the crystal incorrectly affects both frequency and startup time if I'm not mistake.)

RE: Custom nRF52 board partially start

Fabien Comte — Sun, 28 Feb 2016 10:36:33 GMT

And of course, thank you both (run_ar and RK) for your helps.

RE: Custom nRF52 board partially start

Fabien Comte — Sun, 28 Feb 2016 10:34:55 GMT

Hello, 10 pf it was in the second comment :-) for selftest ok, but i presume that i have to run on RC HF in case crystal HF clock don't works, right ?

RE: Custom nRF52 board partially start

RK — Sat, 27 Feb 2016 03:09:53 GMT

I'm confused by the load capacitance discussion. The crystal should be fine, you just need the correct load caps on the board to match it. However I don't know how run_ar knows you have 10pf caps on there, perhaps he has secret information about your board layout to which I'm not privy!

If you switch the load caps to something closer to 14pF than 10pF (if infact you have 10pF on the board) then you should be close to the 9pF load the crystal wants.

selftest - you could try. Right at the start, before you do anything else, start some kind of timer using the HF clock, start the LF clock, see how long it takes for the LF clock to start, if it starts at all, make a decision that way. That's a test you could run one time on each board and save the result somewhere non-volatile so you start up directly the next time.

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 15:35:30 GMT

And is in code test possible ?

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 15:33:56 GMT

Do you think 18 pf (in stock) are better than 10 pf ?

RE: Custom nRF52 board partially start

run_ar — Fri, 26 Feb 2016 13:31:53 GMT

As far as I can see the load capacitance for the 32KHz is a bit low. spec says 9 while you have 7.
((10+4)*(10+4))/((10+4)*2)=14/2 = 7pf

The RC calibration should work just fine, that is it is stable at a given temperature, but needs to be calibrated if the temperature change. So I would recommend one of calibrate if the temperature has changed option.

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 13:15:20 GMT

I want to do a kind of selftest in code of my 2 oscillators. Is that possible ? start on RC, if KO report and if OK switch to Crystal oscillator.

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 13:13:52 GMT

My 32 MHz oscillator is: EPSON Q22FA12800025 FA-128 32 MHZ 8.0PF

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 13:12:11 GMT

NRF_CLOCK_LFCLKSRC_RC_250_PPM_250MS_CALIBRATION works but i'm not sure of the calibration quality :-)

RE: Custom nRF52 board partially start

run_ar — Fri, 26 Feb 2016 10:37:33 GMT

The product specification for now. Can you try to change the 32KHz source to RC to check if this works. What is your HFXO source?

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 10:28:17 GMT

Is there any document that explain nRF52 clock startup sequence ?

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 10:25:42 GMT

This one: EPSON Q13FC13500003 FC-135 32.768KHZ 9.0PF

RE: Custom nRF52 board partially start

RK — Fri, 26 Feb 2016 09:49:15 GMT

and your board does have a 20PPM 32.769kHz crystal on it?

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 09:48:07 GMT

And after a debug reset it's fast. My oscillator looks lazy.

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 09:46:43 GMT

Fun fact debugger goes out of the function after few seconds but i don't know why ?

RE: Custom nRF52 board partially start

Fabien Comte — Fri, 26 Feb 2016 09:46:05 GMT

SOFTDEVICE_HANDLER_INIT(NRF_CLOCK_LFCLKSRC_XTAL_20_PPM, NULL); and schematic of oscillators is a copy paste of nRF52 DK but with 10 pf instead of 12 pf capacitors.

RE: Custom nRF52 board partially start

run_ar — Fri, 26 Feb 2016 09:28:38 GMT

Can you provide your schematic and init code please? Did you set RC as clock source in SOFTDEVICE_HANDLER_INIT?