[sdiy] CMOS Mux Question

[Seb Francis]

At the moment I have the unused I/O pins left untied and everything 
seems to work ok .. the output CV voltages are spot on and the 
noisefloor is below what I can measure with my (quite noisy) digital 
scope.  So it seems in this particular situation all is ok.  I'll post 
details if I do come across any problems at any point.

Anyway, must go to bed now! .. spent too many hours typing assembly code..

Seb


harrybissell wrote:

>Not tying the unused inputs has caused crosstalk to adjacent
>channels in some MUX I have used....
>
>H^) harry
>
>Magnus Danielson wrote:
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>>From: Seb Francis <seb at burnit.co.uk>
>>Subject: [sdiy] CMOS Mux Question
>>Date: Sun, 16 Oct 2005 02:58:31 +0100
>>Message-ID: <4351B3C7.3030508 at burnit.co.uk>
>>
>>    
>>
>>>Hi,
>>>      
>>>
>>Seb,
>>
>>    
>>
>>>I've just built a MIDI2CV converter for my Oakley 3031.  It's using the
>>>same PCB I used for my 15xCV modular converter, but since I don't need
>>>this many CVs I'm only fitting the required number of S&H caps and
>>>output buffers.  This means that I have the unused outputs from the CMOS
>>>Mux left not connected to anything.
>>>
>>>The Mux in question is the MAX306.  It doesn't say anywhere in the
>>>datasheet that you have to connect every input/output, but I remember
>>>that this is generally a good thing to do with CMOS ICs.  Does anyone
>>>have any advice on the matter?
>>>      
>>>
>>The analog mux inputs/outputs is a special case. You can leave them open.
>>The digital inputs to the mux is like any other CMOS input, don't leave them
>>open, but I guess you would not do that anyway since you are using it.
>>
>>    
>>
>>>Will it have any bad effect just to leave the unused outputs not
>>>connected?  The uProc software will never switch the input to them.
>>>      
>>>
>>The only thing which comes to mind is ESD protection. I would recommend you to
>>tie the inputs/outputs down to ground with a resistor.
>>
>>You should be able to find the answer if you read the datasheet carefully.
>>
>>Cheers,
>>Magnus
>>    
>>
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