For best operational performance of the device,
use good PCB layout practices, including:
- Noise can propagate into analog
circuitry through the power pins of the circuit and directly through the
operational amplifier. Bypass capacitors help to reduce the coupled noise by
providing low-impedance power sources local to the analog circuitry.
- Connect low-ESR, 0.1µF
ceramic bypass capacitors between each supply pin and ground, placed as
close to the device as possible. A single bypass capacitor from V+ to
ground is applicable for single-supply applications.
- The OPA6x7 is capable of high-output
current (in excess of 45mA). Applications with low impedance loads or
capacitive loads with fast transient signals demand large currents from
the power supplies. Larger bypass capacitors such as 1µF solid tantalum
capacitors can improve dynamic performance in these applications.
- Separate grounding for analog and
digital portions of 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 EMI noise
pickup. Make sure to physically separate digital and analog grounds paying
attention to the flow of the ground current.
- To reduce parasitic coupling, run
the input traces as far away from the supply or output traces as possible. If
these traces cannot be kept separate, crossing the sensitive trace perpendicular
is much better as opposed to in parallel with the noisy trace.
- Place the external components as
close to the device as possible. As shown in Figure 7-10, keeping RF 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.
- Consider a driven, low-impedance
guard ring around the critical traces. A guard ring can significantly reduce
leakage currents from nearby traces that are at different potentials.
- The case (TO-99 metal package
only) is internally connected to the negative power supply, as with most common
operational amplifiers.
- Pin 1, 5, and 8 of the SOIC
packages have no internal connection. Pin 8 of the TO-99 packages has no
internal connection.
- Cleaning the PCB following board
assembly is recommended for best performance.
- Any precision integrated circuit
can experience performance shifts due to moisture ingress into the plastic
package. Following any aqueous PCB cleaning process, baking the PCB assembly is
recommended 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.