[sdiy] CMOS Mux Question

[Seb Francis]

Hi Harry,

Thanks for the answer.

harrybissell wrote:

>You could tie them down (or up) but if you accidently turned them
>ON you might get high current from the input pin.
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>Why not tie them migh, or low, through a pull down (up) resistor ???
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If I was going to tie them I would tie them to ground via a common 10K 
resistor, but this means soldering extra connections on my PCB that I 
would have to de-solder later if I want to add more channels.

>(strictly speaking, I don't think you need to tie them at all...)
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I'm hoping this is the answer :)
(I guess because the input/output pins in question are strictly speaking 
analog pins, not CMOS logic?)

>What does the data sheet / app notes say ???
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Well it doesn't 'say' anything in the datasheet, but on some of the test 
curcuits the unused input/outputs are shown connected to ground.
The only app note I could find doesn't say anything either ..
http://www.maxim-ic.com/appnotes.cfm/appnote_number/684

Seb


>Seb Francis wrote:
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>>Hi,
>>
>>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?
>>
>>Will it have any bad effect just to leave the unused outputs not
>>connected?  The uProc software will never switch the input to them.
>>
>>Here's the datasheet for the MAX306..
>>http://pdfserv.maxim-ic.com/en/ds/MAX306-MAX307.pdf
>>
>>Seb
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