Overvoltage and ESD protection for analog I/O

Hi,

I creating board with basic Atmega328P.
My task - create overvoltage and ESD protection analog pin.

I searched protection example with Ruggeduino board:

Questions:

  • Does it work on an analog pin? Or just digital pin.
  • The description said about protection against increased voltage. Will it work on ESD? Or is it necessary to look towards TVS diodes?
  • The resistance of my PTC fuse is 0.09 - 0.35 Ohm. In the diagram, the fuse resistance is 220 Ohms. Is this resistance after tripping? If not, should I add such resistance in series to the fuse?

For ESD suggest you use bidirectional Transorbs to EARTH ground.

A zener/TVS is a poor solution, because it does not protect when the Arduino is off.
A zener/TVS is not perfect near the zener voltage, so analogue voltages will be compressed near the top, giving false readings.
Best solution is clamping diodes to VCC and ground, but make sure you use the right ones that conduct BEFORE the internal ones do.
Read this.
A polyfuse is slooooow, and useless to protect a pin.
Leo…

Does it work on an analog pin? Or just digital pin.

On an analogue pin it distorts the reading of voltages above about 4V because of the zener's knee starts to draw current at this sort of voltage.

3.The resistance of my PTC fuse is 0.09 - 0.35 Ohm. In the diagram, the fuse resistance is 220 Ohms. Is this resistance after tripping? If not, should I add such resistance in series to the fuse?

The resistor in the diagram is a resistor. :wink:

Under normal-voltage conditions the diode doesn't conduct. Since the Arduino inputs have "nearly infinite" resistance, essentially zero current flows, and with no current through the resistor no voltage is dropped/lost across the resistor.

When the diode conducts (either direction) current flows through the resistor & diode and any "excess" voltage is dropped across the resistor. The resistor limits current through the diode so the diode doesn't get damaged.

BTW - This is exactly how an LED & resistor work together... The "excess" voltage is dropped across the resistor and the resistor limits current.