HSE crystal dead

[Nico3]

Hello

I am trying to powerup external 8MHZ crystal on STM32F407VET6 MCU but it is completely dead. I run the LED bliking program using HSI, and it is working sucussfully. Boot 0 and Boot1 pins have been PD with 500 ohm. 

 I also run the same code to use HSE on STM4 Discovery board after removing R68, I see HSE on board is working. 

Below are my caclulation

Frequency = 8 Mhz,

Co = 7 pF ( as per datasheet)

CL= 10 pF ( as per datasheet, used 20pF CL1 and CL2) 

ESR = 100  ohm ( as per data sheet)

After calculation gmcrit comes..

gmcrit = .287 

gm =  5 ( from ST data sheet)

gain margin = 5/.287 = 17    

so gain margin > 5 condition is met. 

I also changed Rext  to 0, 100, 200, 500 , 1000 ohm. HSE is dead. 

PCB design seems ok , and I assume for now no issue with PCB design.

I have gone through AN2867, but not sure what point I am missing.

Kindly suggest where could be the fault.  I eliminate software issue as same code is making HSE work on Discovery board.

[LCE]

@Peter BENSCH thanks for the reply!
So the LSE is usually the sensitive part, and I understand that for power saving reasons it's high impedance -> low power - but more sensitive

> All in all, it is therefore highly recommended to ensure a super clean layout for the crystals ...

Definitely! Sometimes a little hard for the beginners, but my experience with other ICs is that there were never any problems - even with my first "bad" PCB layouts 25 years ago. 😉

Just saying that the AN sounds as if 3 mm too far away and everything breaks down.

Looking over the HSE / user problems here, most of the time it was a broken component or the caps were far from the recommended values - or not mounted at all.