AnsweredAssumed Answered

ADAU1702 oscillator start problems

Question asked by ElmarJ on Nov 2, 2015
Latest reply on Nov 9, 2015 by DaveThib

Hi,

 

I am having problems with the oscillator of my ADAU1702 not startup up. The problem is very comparable to the problem described in this discussion: (only ADAU1702 vs ADAU1701, my risetimes are even shorter).

1701 Oscillator start problem

 

I have searched the datasheet for risetime spec`s of the power supply, but I cannot find them.

 

Our system is using a 3v3 buck regulator from 12 .. 20V input, and our host MCU uses a FET to enable this 3v3 rail to the ADAU. Attached you can find the risetimes (ch2) and oscillator out pin of the ADAU. As you can see the oscillator does not startup reliably.

 

WP_20151102_001.jpg

 

WP_20151102_14_11_34_Pro.jpg

WP_20151102_14_16_44_Pro.jpg

 

layout.png

 

Our board is a 4 layer board with solid groundplane on an inner layer, and also with a supply plane.

 

What should be the rise times?

Outcomes