I need to protect my GPIO from Electrostatic discharge as my inputs are coming from outside.I am using LPC2132 Micro controller which uses +3.3V Supply.Bidirectional ESD diodes that I have seen so far has maximum clamping voltage 0f 7V. Since the micro controller does not withstand more than Vdd+0.3V,I am confused how to protect the micro controller.Is there any way to protect from Electrostatic discharge other than TVS diodes
Digital input pins will normally have something stated in the data sheet about the maximum current that can be fed into an input. Normally, the input current is nano amps but when an input voltage rises above the positive rail this current can sky-rocket. Ditto when an input falls below the negative rail.
The DS might say that the maximum current is 1 mA - this gives you something to work with because, an input pin can have a resistor placed in series with it. For example, if an input pin rose by 0.3 volts above the 3V3 rail then there is a danger of too much current however, if there was a 1 kohm resistor in series, you could raise that input voltage to 4.3 volts at the risk of only 1 mA flowing.
So, by adding a series resistor you are giving yourself an easier job of input protection. If 5 mA is allowed, a 1 kohm resistor will give you 5V extra protection beyond the 3V3 +0.3 volts you specify in the question.
Protection offered by a 7 V device is now clearly feasible.