Hi champs,
My customer found that the external 20MHz crystal failed to start-up while processing the returned products, he conducted some experiments and got below results.
- When crystal fails to start-up, the impedance of X1 pin is dozens of KΩ, and the voltage of X2 pin is 0V.
- When the product that is not powered on is left for several hours, the impedance of X1 pin could be several MΩ. If my customer power on the product and crystal can start-up for minutes and then fails again.
- Input 20MHz clock source into X1 pin(leave X2 floating), then F28374D works without problem.
- Replace the 'NG' crystal with a 'GOOD' one, the problem is still there, 20MHz crystal fails to start-up.
Below table is the spec of my customer's crystal for reference.
Below is the schematic of crystal circuit for reference,
- R16 = 510Ω.
- R17 = 1MΩ.
- C20 = C21 = 15pF.
It seems that there are something wrong with F28374D, please advise your comments on this situation, do you see any problems? what can we do for further investigations?
Thanks,
Luke
