11.1 Layout Guidelines

All logic signal wires and leads should be grouped and kept as far away as possible from the analog signal leads. Exposed leads to the analog inputs can cause undesired digital noise and 60-Hz pickup. Shielded leads for the analog inputs may be required in sensitive applications. A single-point analog ground should be used that is also separated from the logic ground points. The power supply bypass capacitor should be returned to digital ground. Any V_REF/2 bypass capacitors, analog input filter capacitors, or input signal shielding should be returned to the analog ground point. A test for proper grounding is to measure the zero error of the ADC converter. Zero errors in excess of 1/4 LSB is generally traceable to improper PCB layout and/or wiring.

To minimize potential offset issues, TI recommends to route the signal traces differentially next to each other so that they will see the same thermal gradients and the same number of feedthroughs. Furthermore, inductance is determined by the size of the loop of current. Providing a path for return currents next to the signal trace will reduce the inductance. A solid ground plane is very advantageous in this regard. Ensure to minimize the loop area formed by the bypass capacitor connection between V_CC and ground. The ground pin should be connected to the PCB ground plane at the pin of the device.