I am using the ADS1235 in a bipolar powered system (AVDD = 2.5VDC, AVSS = -2.5VDC) and the thermal pad is connected electrically and thermally (through multiple vias) to the ground plane. One of my fellow engineers just noticed the ADS1235 data sheet spec'd that the thermal pad to be connected to AVSS. My understanding is the thermal pad is used for heat only (it is not connected to AVSS electrically inside the ADS1235).
AVSS on our PCB is just a trace (not a separate PCB layer or plane).
Question: should we change our PCB layout to connect the ADS1235 thermal pad to AVSS or is it ok to leave it connected to the ground plane? We have been using the Thermal Pad to Ground connection for about a year now and haven't noticed any problems with this.