Even though there are questions about ESD protection for i2c bus already in this forum, I wanted to ask how to suppress the clamping voltage of a TVS diode to a safe level. As an example, the following plot shows the clamping voltage of RClamp0582BQ.
Let's say a microcontroller's SCL, SDA pins are connected to a sensor over wires. Then one wants to protect the chips against an ESD strike caused by human contact. In the circuit below, the TVS diodes clamp the fast transient. The 100 ohm resistors slow down the short current and dissipate power to reduce the stress on the TVS diodes. However, How does one suppress the clamping voltage further ?
(1) an additional ~1k ohm series resistor (as in the image above)
If the device is powered off the impedance of the SCL and SDA pins should be already high, so 1k ohm would not help that much, right?
(2) a ~20pF capacitor
Would it be good to place such small bypass capacitor next to the I/O pins? Since the capacitance should not exceed 400pF, it might be difficult to use a higher value, when there are many slave devices. But I'm not sure if 20pF or something similar is useful.