[sdiy] CMOS Mux Question

[Magnus Danielson]

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