I have a logic input that is 3.3v and I want to be able to allow it to interface with either 3.3v or 5v input signals w/o worrying about it being damaged. I would like to use a resistor with a clamping diode but I'm unsure how to choose an appropriate diode or even what specific type of diode is the right one to use.
What are the relevant specifications I should look for when choosing a diode to clamp an input signal to 3.3v?
Best Answer
Use a diode that is fast enough to handle the voltage changes on the line. Check for the current that will flow though the diode and make sure it can handle that.
Simply, a Schottky diode with a rating of 50mA to 100mA should suffice.
Alternatively, use a voltage divider with a division ratio of: 5V/3.3V = 1.51
It will also work for 3.3V: 3.3V/1.51 = 2.18V
Because 2.18V is above the minimum voltage level for logic 1.