Section 7.2 shows that the PGA854 output-stage fully-differential amplifier uses 6.67kΩ feedback resistors between the OUT+ output and the inverting input, and the OUT– output and the noninverting input. External direct access to inverting input is provided through the FDA_IN+ pin, and to the noninverting input through the FDA_IN- pin. This option allows circuit designers to add external feedback capacitors in parallel with the internal feedback resistors to implement noise-filtering or noise-shaping techniques. These pins are also usable to implement customized attenuating gains for the output stage. Consider the following important factors when designing parallel circuits with the internal feedback resistors:

• The accuracy of the internal resistor network is 0.01% or better. This accuracy results in a common-mode rejection ratio (CMRR) of 80dB or better. Mismatched leakage currents on these pins potentially causes CMRR degradation.
• The internal resistors have ±15% absolute resistance variation; consider this variation when implementing custom attenuating gains or noise filters.