Hello,
We are experiencing some problems with crystals stopping after a while when used with an ADS1242 ADC. In some cases, failure can occur after over a year of continuous operation whereas on other units, they fail first time round (just after production).
I've read other forum posts regards crystal problems, in particular the post "ADS1256 Crystal oscilator start-up problems" by Josko Marasovic. I've also read other articles relating to crystal problems where they mentioned that exceeding the maximum drive level (power dissipation) of a crystal can lead to an increased rate of aging and Drive Level Dependency problems.
Can you please explain or specify the following:
1. What is the drive Level of the ADS1242 crystal circuit?
2. Will the drive level be sufficient for all crystals (or even too much)?
3. How do the crystal capacitors affect crystal start-up? Why would smaller caps be better?
4. Most crystal manufacturers give the equation CL= [(C1*C2)/(C1+C2)] +Cstray to determine the crystal caps. Using this seems to result in larger caps for C1, C2 than suggested in the ADS1242 datasheet. Why is this?
5. What is the stray capacitance of the crystal input pins?
6. Any other suggestions as to why units stop working after a while?
Thanks,
Kieran