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Re: [ts-7000] Re: Odd effect ADC sampling LED on TS7250

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Subject: Re: [ts-7000] Re: Odd effect ADC sampling LED on TS7250
From: Jason Stahls <>
Date: Sun, 18 Oct 2009 23:20:27 -0400
j.chitte wrote:
> Could you comment on my understanding that the MAX197 in 0-5V mode is 
> floating the input at 2.5V and hence requiring the op amp to sink current 
> when the input is <2.5V ?

 From my quick lookover of the datasheet I don't believe that's the way 
it's supposed to work.  On page 8 of the PDF it shows a equivalent 
schematic of a single input channel.  That shows a 12.5k series resistor 
on the input, then a 5.12k pull-up to the voltage reference that's only 
used in bi-polar mode and a 8.67k pull-down to GND.  I don't see any 
reason in that why your showing a 2.5v float on the pin, unless it's 
using a external 2.5v reference and in bi-polar mode.  Tried another MAX197?

-- 
Jason Stahls


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