The feedback network on the OPA3S2859RTWEVM has been optimized to minize capacitive coupling between the feedback traces when typically using feedback resistors of 1 k-Ω, 10 k-Ω, and 100 k-Ω. This was done by spacing the feedback network and pouring ground between the traces to isolate the capactive coupling. The tradeoff to this optimization is that it can make the amplifier unstable for low gain or attenuator configurations. For applications that have lower gain, the feedback network area can be reduced to minimize the trace inductance and capacitance to ground, which will help stability at low gains. The EVM includes footprints for suggested 10-Ω isolation resistors between the feedback trace and output pin to help isolate some of the added inductance and capacitance from the feedback area.

The board layout also includes an optional pad to connect a resistor between the IN- pins and the feedback network trace by using the existing footprin for R9 or R16. This allows the user to add an optional fourth feedback path in parallel with the existing three feedback connections.