I corrected a problem with ACX !ACX lines driving analog switches in a bipolar ac excitation load cell application. All seemed OK.
But always results come as 0. I tried running combinations of internal and system self-calibrations and the 7730 hangs. This is the second IC I have tried. All voltages are nominal as AFAIK, even 5.3V max between AGND (set to -2.3V) and VDD (3.0V). AVDD is set for 2.3V.
I read that the AD7730 REF inputs are not buffered. This is a 6-wire load cell, so the REF inputs are going through a string of resistors to drop from +/-5 to +/- 2.2V (approx). The resistors are 9.1K - 16K - 9.1K. IC hangs using both AC mode and non-AC mode. I cannot manually set the gain and offsets either. If I just run the IC without calibrating, everything cycles, I can change frequency, etc. But it will NOT calibrate. CHOP="1" (sometimes "0" with non-AC modes), HIREF is "1", !B/U is "0".
I have not had any problems with this IC in 0-5V applications. Are there any particular settings that need to be observed in bipolar mode?
Is there an alternative, more modern IC I should be using instead?