In this volatile world, you always expect lot of noise around, unexpected voltages being applied by voltage. Protection against such scenarios is very important. For example, take the scenario of I/O pins of the micro controller, if you have configured the I/O pin as input and providing an input, there can always be a chance where by mistake we provide high voltage on that pin. There could be a chance of ESD as well. So, these days micro controllers come up with a protection to handle such scenarios. A point to mentioned here is that most micro controllers have I/O pins which are 5V tolerant for a power supply operation of 3.3V of the micro controller. Consider the below protection mechanism used in PIC16 micro controller.
The same circuit has been tried to be simulated in TINA to understand the functionality. Below is the circuit simulated.
The above circuit is seen applying a high voltage of 12V for a 5.5V tolerant I/O pin. In this scenario, once the 12V is applied, the 1K helps limit the current at first instant. Once the voltage of 12V is
seen initially at D1 anode, the diode shall be ON and pin is clamped to a voltage of 5.5V. The below result post simulation shows the same scenario.
Consider the same circuit for an input of 24V for V1 input and you can see that the voltage is clamped,
All the modern day micro controller have this protection. Designer has to study the respective datasheets of the micro controller to understand these circuits and protection provided.
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