ADS8688A: RS resistance of analog input terminal

Hello, please see my response in-line

Table 1. Input Overvoltage Protection Limits When AVDD = 5 V or Offers a Low Impedance of < 30 kΩ

If RS in Figure-68 is less than 30kΩ, does this mean that there is no problem?

Perhaps, I think that 30kΩ is not about RS, but about the impedance of the AVDD line.

This is about the AVDD line and not Rs. Note that the protective diodes are connected to the AVDD line, in figure 68 that means that current will be directed to AVDD.

If I can, I can see the sentence that you want it to be close to 0Ω.

"The results indicated in Table 1 are based on an assumption that the analog input pins are driven by very low impedance sources (RS is approximately 0)."

This sentence is about Rs and explains the tradeoffs of a higher or lower value for Rs. With a low Rs value, this is better for accuracy and performance. With higher Rs the current is decreased and OVP range is increased, but this impact negatively the device performance.

In my circuit, I design with RS of 470Ω.

Moreover, noise reduction is carried out by putting 0.1uF in AIN_nP and AIN_nGND after RS.

If there is a problem with such a circuit, I would like advice.

This sounds fine in general, what is driving the input?

I am concerned about the last sentence on Page-25 of SBAS680.

"Note that higher source impedance results in gain errors and contributes to overall system noise performance."

How large does "higher source impedance" mean?           

This would be a resistor in the kilo ohm range, for example

Regards

Cynthia