Hi Kai, The red point is the input voltage to the customer's system. The first resistor and TVS diode are optional, but in general I would recommend trying to shunt any overvoltage or EMI signal to earth/chasis ground before entering the system as this helps to protect sensitive components inside the system. Most of our ADCs can tolerate up to 10mA of continuous current flow through the internal ESD diodes; therefore, the input protection circuitry should ensure that current flow is limited to something below this value to prevent damage to the IC. The most relevant TI design I can point to is www.ti.com/.../TIDA-00548 . I hope that helps!
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