11.1 Layout Guidelines
For best operational performance of the device, use good PCB layout practices, including:
- Use bypass capacitors to reduce the noise coupled from the power supply. Connect low ESR, ceramic, bypass capacitors between the power-supply pins (V+ and V–) and the ground plane. Place the bypass capacitors as close to the device as possible with the 100-nF capacitor closest to the device, as indicated in Figure 68. For single-supply applications, bypass capacitors on the V– pin are not required.
- Separate grounding for analog and digital portions of the circuitry is one of the simplest and most-effective methods of noise suppression. One or more layers on multilayer PCBs are usually devoted to ground planes. A ground plane helps distribute heat and reduces electromagnetic interference (EMI) noise pickup. Make sure to physically separate digital and analog grounds paying attention to the flow of the ground current. (For more details, see the Circuit Board Layout Techniques chapter extract.)
- In order to reduce parasitic coupling, run the input traces as far away from the supply or output traces as possible. If the traces cannot be kept separate, crossing the sensitive trace perpendicular is better as opposed to in parallel with the noisy trace.
- Minimize parasitic coupling between +IN and OUT for best ac performance.
- Place the external components as close to the device as possible. As illustrated in Figure 68, keeping RF, CF, and RG close to the inverting input minimizes parasitic capacitance.
- Keep the length of input traces as short as possible. Always remember that the input traces are the most sensitive part of the circuit.
- Cleaning the PCB following board assembly is recommended for best performance.
- Any precision integrated circuit can experience performance shifts resulting from moisture ingress into the plastic package. Following any aqueous PCB cleaning process, bake the PCB assembly to remove moisture introduced into the device packaging during the cleaning process. A low-temperature, post-cleaning bake at 85°C for 30 minutes is sufficient for most circumstances.