But which equation you used to arrive at 47.7 ns ? Please tell me how have you calculated tau (time constant) ? How have you arrieved to " after 1ns voltage drop across transorb is about 5.99v." ?

Like that:



If we use a 10K resistance before Transorb how to calculate time constant.

It's wise to do that, because 10k resistor will also suffer from ESD event. In the other thread a very high power type of 10k resistor was used, which can more easily withstand ESD events. But such type to use with mcu ports is not wise...

I also want to know can we protect the analog ports with transorb also and omit the ISOLATION AMPLIFIER ? (current loop case 4ma to 20ma)

This I can only answer, when seeing whole circuit and knowing enough about environment. But statements given in my last reply can show the 'direction'. Normally Schottky diodes at inputs are not used, because of it's too high leakage currents. So, fast silicon switching diodes like 1N4151 should be used, or parts with even lower leakage currents. Also, adding of additional capacitors is widely used for absorbing part of ESD energy and slow down rise time at succeeding circuitry, so that 1N4151 is fast enough to canalize ESD energy to Vcc or ground.

ESD protection scheme for analog circuitry must be developed very properly. Otherwise, functionality will suffer from additional leakage currents or offset voltages.

Kai