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ADAU1701 /1401 Recommended Crystal Layout

Question asked by euanbrown on Jan 21, 2018
Latest reply on Feb 5, 2018 by Les_K

Dear Analog,

 

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.

http://www.analog.com/media/en/technical-documentation/data-sheets/ADAU1701.pdf  

 

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

ADAU1701 crystal layout

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