11.1 Layout Guidelines
The OPA835 EVM (SLOU314) can be used as a reference when designing the circuit board. TI recommends following the EVM layout of the external components near to the amplifier, ground plane construction, and power routing as closely as possible. General guidelines are listed below:
- Signal routing must be direct and as short as possible into an out of the op amp.
- The feedback path must be short and direct avoiding vias if possible, especially with G = +1.
- Ground or power planes must be removed from directly under the negative input and output pins of the amplifier.
- TI recommends placing a series output resistor as close to the output pin as possible. See Figure 41 for recommended values for the expected capacitive load.
- A 2.2-µF power-supply decoupling capacitor must be placed within two inches of the device and can be shared with other op amps. For split supply, a capacitor is required for both supplies.
- A 0.1-µF power-supply decoupling capacitor must be placed as close to the supply pins as possible, preferably within 0.1 inch. For split supply, a capacitor is required for both supplies.
- The PD pin uses TTL logic levels. If the pin is not used, it must tied to the positive supply to enable the amplifier. If the pin is used, it must be actively driven. A bypass capacitor is not necessary, but is used for robustness in noisy environments.