select crystal to STM32F207

[artemi]

Posted on September 04, 2014 at 12:28

Hello,I am a student that is designing a prototype with STM32F207VC. I'm trying to choose a 25 MHz crystal oscillator to have ethernet, with AN2876 guide. I see in this guide the recommend crystal STS25ASM , but when I do the calculations of the guide the results are not valid.The external capacitors values are 30 pF, and the result of the gain margin, assuming the gm is 5, is 2.15. Why this crystal is recommend?Other question, which is the typical value of vpp value in calculating drive level?thank you,

[Tesla DeLorean]

Posted on September 04, 2014 at 18:33

For the less dyslexic that's

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/CD00221665.pdf

and

http://www.mouser.com/ds/2/96/008-0309-0-32667.pdf

Choosing a ''crystal oscillator'' or XO, would suggest you're picking an oscillator, not a cut crystal in a can.

Consider if the PHY you are choosing can generate it's own clock, and supply that to the STM32.

Look  also at what ST uses in there own boards.

http://www.hosonic.com/admin/upload/pro201112311246052.pdf

[re.wolff9]

Posted on November 02, 2015 at 17:41

I have checked your suggestion: ''use the one that ST uses''. As far as I can see the relevant parameters (C0, CL, DL) in the two datasheets are EXACTLY the same as the one the TS uses (

http://www.mouser.com/ds/2/96/008-0309-0-32667.pdf

). 

[Tesla DeLorean]

Posted on November 02, 2015 at 18:34

The ESR looks different. I really hate these datasheet where one generic sheet covers 100's of different parts with slightly different characteristics.

ST uses this crystal with a 390 Ohm series resistor, and 20pF decoupling to ground.