I'm using AD8275 for my project to scale the +/-10V bipolar singal to unioplar 0-4V so that it could be accepted by a 5V ADC. According to the typical appication circuit of the data sheet,i built a minimum one based on this chip.During testing,i found that it worked well for positive signals,but the scaled output was not so accurate as i expected when input was switched to negative range.Can someone help me figure out what the probelem lies in? I attach some measured and calculated value here.
** The measured reference voltage(VREF) is about 4.1V** VOUT = VIN / 5 + VREF / 2
VIN Measured Value Calculated Value+9.5V 3.95V 3.95V+7.5V 3.55V 3.55V+5.0V 3.05V 3.05V
0.0V 2.05V 2.05V
-5.0V 1.04V 1.05V -7.5V 0.54V 0.55V-9.5V 0.12V 0.15V
It's clear that the accuracy is not satisfied when VIN goes to negative.
Thank you in advance.