On of our customer has made measurements on the crystal input (between xtalp and gnd). Currently they are performing some hardware tests and identified a potential problem regarding the signal levels on the crystal inputs. If they interpret the datasheet
correct, the clock signal has to have a swing between 0.4V and 1.2V to guarantee proper function?
In their case the maximum voltage level of the signal is only 1.1V in room temperature, which does not look good in relation to the
specifications. And when they are preforming stability tests with a negative resistance the voltage drops a lot more.
Since we are unable to adjust any drive strength for the XTAL pins I wonder how we should do to improve the performance?
We are using a 28.66363MHz crystal with two 47pF capacitors connected to ground, se figure.
In the back of my head I recall that measuring directly on a crystal input is not a good idea as they are very sensitive to any thing that you hook up to it (probes etc). My guess is that we guarantee this by design and no actual test. Correct ? Any opinions on this topic ?