Other Parts Discussed in Thread: OPA2835, , OPA365
The datasheet of the ADS7947 mentions in Fig 52 (input driving circuit with opamp) as well as in Fig 53 (input driving circuit without opamp) that R1 should be 5 Ohm. I am looking at an application with OPA2835 opamp and ADS7947 ADC. With 470pF input capacitor and twice 5 Ohm, the OPA2835 will become unstable since the series resistor at the opamp output is 10 Ohm with 470+32 pF load.
The OPA2835 can not drive too high capacitive load. A minimum series resistor must be placed at the output of the opamp in series with the capacitor of 470+32 pF load. According to the datasheet of the OPA2835 it must be substantially higher than 15 Ohm to have stable system.
To have enough safety margin (lets says factor 3), we would propose to use 2 x 22 Ohm (44 Ohm in total).
Question : can we modify R1 resistor from 5 to 22 Ohm and at the same time to make the output resistor 22 Ohm as well to have a symmetrical loading at the ADC inputs? Remember that in the datasheet of the ADC (ADS7947), R1=5 Ohm is recommended.
