SON VUONG

908LJ24 32.768KHz crystal start-up problem

Discussion created by SON VUONG on Dec 8, 2009
Latest reply on Dec 20, 2009 by ikauf ikauf

I am using the 908LJ24 with the 32.768KHz crystal set up in similar configuration as shown in the MONITOR section of the data sheet (Rs=330K, Rb=10M, C1=C2=22pF).

Recently I encountered a problem that the circuit randomly refused to power up. After a series of testing and debugging of both hardware and software, it was discovered that for some reason, at the power up, the crystal circuit intermittently failed to start. The only way to bring the circuit back to live was either disconnecting and re-applying the power to the circuit or injecting an external signal to OSC1 pin of the micro-controller. Reset signal did not help at all in this situation.

The headache of this problem is in its randomness, The circuit could go for days without any problem in the same environment (room temperature, low humidity, regulated power supply) and then exhibited the symptom without any warning.

I am sure there may be a lot of factors involved but I could not get to any thing that can consistently make it happen so that I can verify the root cause and eventually come up with the fix.

If anyone of you have come across this problem before and know of a way to trigger the problem to happen at a fairly predictable manner, I would appreciate all the help.

Just in case you wonder, the product has been manufactured for a customer since 2006. The circuit did not change much over the years but the problem just surfaced recently.

In the course of analysis, I tried different crystal manufacturers, different values for crystal circuit components. None of them actually made any difference.

Thanks.

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