[sdiy] DG409 blues

[David G. Dixon]

> The Intersil datasheet indicates the absolute max voltage on the digital
> inputs is (V-)-2V, to (V+)+2V, or 20mA. The 20mA limit is to guarantee
> you don't blow up the protection diodes on the inputs if you exceed the
> rails.  So you shouldn't hurt the device if it's powered from +/-15 and
> the inputs don't exceed that.

Yes, that's what I figured, too.  In this application, the EN input is
simply held on all the time.  I wish it was a low-level on, but it isn't.  I
just wired it directly to the +15V rail.  However, the problem is definitely
occurring on the switching.

> Do you have a two channel scope?  Hold all the analog inputs constant,
> and trigger on the one of the digital inputs changing.  Monitor the
> output and see if it is glitching due to the digital input changing.  If
> so you could try reducing the digital inputs with some simple resistive
> dividers and see if that makes a difference.  Analog switches have a
> spec called 'charge injection' that could be in play.  There's a good
> reference here:
> http://www.analog.com/library/analogDialogue/archives/31-3/ask.html

I do have a 2-channel scope, and I will try what you say.  Concerning charge
injection, that's the whole point of using DG409 instead of CD4052!  It
would be nice if the datasheet showed some specs relative to changing
digital levels.  I guess I'll find out if these levels are important or not.

Thanks to everyone who responded for all the help.  I'll let you know how it
all turns out.