[sdiy] CMOS Mux Question

[harrybissell]

Not tying the unused inputs has caused crosstalk to adjacent
channels in some MUX I have used....

H^) harry

Magnus Danielson wrote:

> 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