Why is my ADuC836 slow to lock to the external crystal?

Document created by analog-archivist Employee on Feb 23, 2016
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The ADUC836 on power up starts with PLL free running, it only locks to the
external 32K crystal after a second power up. What could be the problem?


The ADuC836 is designed to operate as follows:
Lock must be achieved within the first second after power up, but once detected
this will be remembered until the next power down. There is no way for the user
to force lock.

Apart from an oscillator which takes a long time to start, there are 2 other
known conditions causing the problem.

The first is noise on the power supply.

The second is capacitive loads or a poor crystal on the crystal pins
- to make this very clear - there should not be any capacitors on the crystal