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Subject: Re: Switching between analog inputs

Date: 12/20/01 at 10:37 AM
Posted by: Dominique
E-mail: dominiquebovey@netscape.net
Message Posted:

In Reply to: Re: Switching between analog inputs posted by John Dunn - Consultant on 12/19/01 at 10:45 PM:

Hi,
I have been using using CD405x multiplexers
to switch several inputs to an ADC dynamically
(on a sample-per-sample basis) and they were too
slow so I changed to the MAX405x. But John
is wrong, the CD405x is meant to be powered with
+- supplies and NO digital supply, just like the
DG40x. But
- take care with the VEE and VDD
denominations in some data sheets, I had once 18
chips frying when we applied power on a new board!!!
- take also care with the switching levels on the
digital inputs vs. the power supply voltage
- for the CD405x and CD4066 the on resistance
changes drastically with the ps voltage!
So as answer for angelo's original question I
would use a low cost CD4053 or higher cost MAX4053,
(triple 2-to-1 multiplexers), or a CD4066 with a
logic inverter.
Season's greetings and have a nice holiday
Dominique


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