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ADAU1701 Start-up Problem

Question asked by platonik on Jan 6, 2011
Latest reply on Jan 7, 2011 by platonik

Hello, I'm seeing bizarre behavior from my ADAU1701. The chip works perfectly half of the time when power is supplied and does not the other half of the time.


When the chip works, the voltage on the CM pin is 1.52 V (roughly). When the chip does not work, some of the times the CM voltage will be around 1.52 V and locked in at a value (say, 1.48 V some times). Other times when the chip is not working, the CM voltage will start either high, say at 2.2 V and fall over time or will start low, say 0.33 V, and rise over time. I also notice that when the chip is not working and the CM voltage is either rising or falling, I can change the speed of ascent/descent somewhat by pressing my finger around the external PLL circuitry (pressing this area when the chip is working has no effect).


The current draw from the chip varies as well. When the chip works, current draw is around 180 mAmps. When the chip does not work, the current draw is around 70 mAmps.


I have each of my power rails, e.g. AVDD, PVDD, IOVDD, and DVDD, separated from each other by ferrite beads and have all supplies well bypassed with electrolytics and ceramics. I also have the CM pin AC coupled to ground through a 100nF MLCC and a 56uF electroltyic. All other pins requiring bypass capacitors are bypassed accordingly.


I have actually done two board revisions and installed multiple chips that all exhibit the same problem.


Any and all help is greatly appreciated. If more information is needed as well regarding setup, please ask.




- Chris