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From EVAL-ADAU10701MINIZ to a project...

Question asked by 3.3V on Jan 1, 2013
Latest reply on Jan 7, 2013 by ColemanR

Hello everybody and happy New Year!


This is my second post. I hope I’m posting in the right place…


A few days a go I purchased an EVAL-ADAU10701MINIZ. I’m new to DSP but I managed to put together a couple projects in SigmaStudio.


My next step is trying to build a circuit board that uses the ADAU1701. The idea is use the evaluation board schematic as a starting point.


There are a few things I am not sure I entirely understand:


1) I measured the frequency response of the EVAL board and I noticed a cut of the high frequencies. Around -1dB at 9 kHz going down as the frequency increases. The out filters are set at around 50 kHz. Is this due to the input filters?


2) The connector J8 indicated a USB_CLK signal coming from the iUSB. I can’t see the signal be used anywhere in the EVAL board schematic. Is it used in some way that I can’t see? Does it have to be connected anywhere?


3) There is something that doesn’t entirely convince me in what I think is the Writeback Trigger (Q2 circuit).


Q2 senses the power supply using DVDD. It kicks in when it senses a drop. However, C15 and C16 sustain DVDD but also the writeback trigger. Q2 cannot sense the power drop as it is “hidden” by the presence of C15/C16. Wouldn’t be the attached circuit more effective? I am not sure but I suspect that as the writeback trigger would be faster, it should be possible to remove C15 or C16 or at least reduce their values. I added C100 but I don’t think it is, strictly speaking, necessary - C45 should be enough.