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AD7266 Erratic Readings

Question asked by Xenthan on Mar 23, 2018
Latest reply on Mar 29, 2018 by jcolao

I have the AD7266 set up with 12 single ended channels, each reading a voltage output from a different resistor divider.  The lower resistors of the dividers are all connected to ground, with the maximum R being about 4Kohms.  Expected value at each divider is about 2.5V, but I'm reading ~1.4V at each.  The strangeness happens when I read from the ADC and also probe the divider with a multimeter.  Once I probe the voltage with the meter, the ADC readings jump to where they should be.  Note that this only happens on the single channel that I'm probing with the meter, the other 11 channels maintain their inaccurate readings.  When I remove the probe, they go back to being inaccurate.  I'm sampling at 2MSPS (5V AVDD, 32MHz clock) and am stepping through each channel sequentially, one reading per channel.  

 

All the GND pins on the chip are properly connected and I've verified that my resistor dividers are properly connected.  Any suggestions on where else I need to be looking?  

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