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Common mode voltage range of the AD7401

Question asked by fseuhs on Mar 13, 2012
Latest reply on Aug 14, 2012 by ShaneO

I have 2 questions about the datasheet of the AD7401 isolated sigma delta modulator.

1. I could not find a specification for the common mode range of the analog inputs. The negative input of the modulator is always connected to GND.

Fot simple operation with a shunt this is OK, but if you want to add some analog preprocessing in front (eg. range switching) it would be very helpful

if the negative inpu could be raised to a potential app. 400mV above GND. Is it possible?

2. You recommend in the datasheet an input filter 2 * 22R + 47pF. This filter has nearly no attenuation at the modulator switchin frequency (some MHz). Usally there is a recommendation for sigma-delta converters to add a simple AA-Filter but with a much lower corner frequency. Why?

 

Many thanks for your answer in advance.

 

F. Seuhs

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