We have designed a system using the ADAU1701 and have experienced inconsistent communication to the unit over I2C and SPI. We have narrowed it down to the crystal oscillator being at fault.
It appears to be an identical issue to a previous post. https://ez.analog.com/thread/9384#33074
When we remove the 100R damping resistor the communications works.
Can Anolog please comment on our findings based on our layout below.
Is there an obvious flaw in our crystal circuit layout?
Is there a recommended PCB layout for the crystal, load capacitors and damping resistor?
Should the damping resistor value be changed?
We are following the recommendation on page 18 of the manual,
Fundamental Crystal, 18pF. (Abracon ABLS-12.288MHZ-B4-T). 22pF load capacitor and 100R damping resistor.
Our layout is shown below. It is a 4 layer stack with a ground plane directly under the DSP and crystal. There is no copper pour on the top layer