Choice and design crystal for STM32F1xx?

[asrock70]

Posted on December 06, 2015 at 13:35

I have a

few questions

for

the design

and choice

of crystals

1. 32.768kHz. In datasheet is Recommended load capacitance max 15pF

In AN2586 is ''To avoid exceeding the maximum value of CL1 and CL2 (15 pF) it is strongly recommended to use a resonator with a load capacitance CL ≤ 7 pF. Never use a resonator with a load capacitance of 12.5 pF''

In  AN2867 is Recommended crystal resonators for LSE oscilátor EPSON FC135 Cl 6pF.  Her is datasheet

http://www.ineltro.ch/upload/cms/user/FC-135_FC-255.pdf

Epson make only 7, 9 and 12.9pF. In my country is

realistically

available

only 12.5pF .

I can

use it

or not

I

use it

a little bit

in it

lose

?

My PCB design,

It is doing

something

wrong

or

it would

do something

better

?

Y2 is 32.768kHz  Y1 is 8MHz

[Tesla DeLorean]

Posted on December 06, 2015 at 16:37

In my country is

realistically

available

only 12.5pF

What does this mean? Which country? It's like saying you can only get micro-farad capacitors, when nano-farad ones are required/specified. It's not an area where a random substitution is going to work.

Of all the parameters critical for the LSE not starting on the STM32F1 parts, being 9 or 12pF is top of the list.

You'll need to find a different vendor/supplier of crystals, and pick a form-factor that is available.

[asrock70]

Posted on December 06, 2015 at 17:59

For example 

http://www.tme.eu/en/katalog/#id_category=112354%26page=1%2c20%26currency=EUR%26s_field=niski_prog%26s_order=ASC%26visible_params=144%2c10%2c2%2c143%2c42%2c118%2c32%2c147%2c36%2c146%2c35%26used_params=10:313%3b42:360723%2c362381%3b144:25243%3b

  in

SMD

have

in stock

only

12.5pF

version .

[waclawek.jan]

Posted on December 07, 2015 at 12:33

In PL (and CZ/SK) you can buy from Mouser through http://www.mausel.eu/?lang=pl with acceptable P&P cost.

JW