I recently bought a DE0 FPGA board with GPIO headers.
The schematics shows that some of them are protected with BAT54S Schottky diodes.
Does it mean that if I input 5v logic level they will be converted to 3.3V and protect the FPGA or do I need to step down the voltage by myself?
What is the easiest-safe way of converting 5v to 3.3v ?
Best Answer
Those diodes protect the pins from overvoltage, undervoltage, and electrostatic discharge. Basically, they prevent the voltage on the pin from crossing outside of the supply voltages, in this case above 3.3 or below 0.
If you want to feed in a 5v signal, put in a series resistor of maybe 100 to 1k ohms or so. The diode will clamp the voltage and the resistor will prevent too much current from being drawn from whatever is sourcing the signal. This only works for low speed signals. If you need something fast, then getting a dedicated level shifter chip is a better idea.