AnsweredAssumed Answered

Gain usage with AD7794

Question asked by Craio on Jun 16, 2014
Latest reply on Jul 23, 2014 by ChrisD.Rama

So i'm trying to read a small signal of about 500mV (done with potentiometer voltage divider) with the AD7794. The use external reference is 3.3V.

When i let the AD do a single conversion the value is what i expect. When i set the gain to two, i get about double of the first value.

However if i increase the gain any further i don't get correct results.

 

Below are the measured values, i've added the readout of the config register to confirm the gain is actually set.

Other settings are: buffered, unipolar, refdetect

 

ch2,GAIN1: 2465896 Config: 0b0001000000110001
ch2,GAIN2: 4927736 Config: 0b0001000100110001
ch2,GAIN4: 6097433 Config: 0b0001001000110001
ch2,GAIN8: 12050114Config: 0b0001001100110001
ch2,GAIN16:14350649Config: 0b0001010000110001
ch2,GAIN32:14119574Config: 0b0001010100110001

 

I expected gain 8 and higher to return full range and an error in the status register, but this doesn't happen.

 

Any idea what i'm doing wrong?

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