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Old 2nd December 2011, 09:21 PM   #1
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Default Filtering PCM 1794 analog output

Hi Folks ! Does anybody know how much filtering ( caps ) is needed at the output of PCM 1794 ? I use 220 pf. across + and - output. Used a Dexa Discret opamp and one of the channels oscilated and burned. The same happened two times for a friend this week.
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Old 2nd December 2011, 10:02 PM   #2
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Why not follow the datasheet? The PCM1794/2 isn't designed to see a capacitive load on its outputs, they are designed to see zero load impedance, that is be connected to a virtual ground. Buffer the outputs with a suitable I/V converter and then perform any filtering you wish, either as part of that buffer, or after it.

I would recommend including a suitable low pass as part of the I/V converter so as to filter out the high frequency stuff and prevent the active device from trying to act on what could be much higher stuff then it can comfortably work with.

As to the size of the capacitors in the network, this is dependent on the network itself, but the corner frequencies that you should have as a target are listed in the data sheet too along with the recommended filters.
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