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SMP04ESZ Sample & Hold drifting

Question asked by Jefff on Sep 19, 2011
Latest reply on Dec 9, 2011 by AndyR

I'm having a problem where the non activated lines from my sample and hold circuit is drifting up.  Everything is fine as long as I am switching at 1 Hz or greater, but in some case I want to keep the hold activated to be able to take a reading. If I keep it held long enough the reading on the other channels will drift up to 6.4 V.  This happens even if all the inputs are grounded.

 

So far I have tried:

 

Adding a buffer in place of R19

Added a pull down resistor to the output lines

Removed the zener diodes and directly connecting a +/- 7.5 V bench supply to +Vcc (pin 16) and -Vcc (pin 13)

grounded all unused input analog and S&H lines

grounded the unused output line

 

None of these seem to work. Any suggestions?

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