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AD7766 full scale ?

Question asked by sasha on Mar 12, 2014
Latest reply on Mar 20, 2014 by jcolao

Hello all !

I use AD7766-2 converter in my project

I apply 5v at Vref+ input from ADR435, and use common mode voltage Vref/2=2.5v.

I checked that Vref/2 in +-5% range!!!

And I apply diff  sin signal (peak to peak) 2.6v p-p   around 2.5v (Vref/2)  to inputs V+ and V-.      Summary:(from 2.5v-1.3v to 2.5+1.3v)

And  I see that ADC overflows !!!!,

 

If apply 2.4v p-p around 2.5, that ADC not overflows but samples from ADC near top level  !!!

 

Why ???

 

In datasheet page 20 say:  "When  the AD7766-2 Vref pin has a 5v supply, the common mode is at 2.5v, meaning that the maximum inputs that can be applied on the differential inputs are  a 5v p-p input around 2.5 v."

 

Why ADC overflows if i apply only littlemore half range ?

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