Hi Bob,
Thanks for your suggestion.
I didn't use prototyping board, I designed a PCB by myself which is used to measure a current (200-500uA). The system has unipower supply 3.3V, AVDD & DVDD tied to 3.3V regulator directly, and AVSS&DVSS tied to GND directly
1. I finally fixed the noise issue by replacing the 0.1uF cap on the VREFOUT pin with a 1uF cap. The system is stable now.
2. My measurement range happens exceed the common mode limit, so I didn't notice this problem. If I want to extend the measurement range, I guess I can tie the AINN to the VBIAS, and connect a reference resistor between AINN and AINP, right? Can the VBIAS sink current?
3. In next version, I want to use a 5V power to the AVDD ( to lower noise), I want to ask if AVDD is sensetive to ripple noise? My idea is use a 7805 to turn 12V to 5V for AVDD, then turn 5V to 3.3V to DVDD, does it work?