Electronic – Using single resistor to receive 5v signal on the 3.3v rated pin

input-impedancemicrocontrollerpinsvoltage divider

I have been investigating ways to safely receive 5v signal on the input pin that can only support 3.3v input signal. I came across an article that states that it's possible to only use a single 10k Ohm resistor to achieve that. I can understand how this can prevent too much current from flowing through the schottky diode, but I am still skeptical this resistor would produce the necessary voltage drop for the signal that goes further into the MCU since the resistance of the resistor that is placed after diodes is much higher than 10k.

Will the 10k resistor work for this purpose and if so, what voltage drop would it produce?

Thanks a lot.

Best Answer

If you are serious about building reliable designs with todays high density chips you should never place a voltage on a pin that exceeds the range specified in the maximum ratings section of the manufacturers data sheet.

People who promote low cost shortcuts, such as the unitary 10K resistor resistor to isolate a 3.3V input from a 5V source, are not serious about building reliable electronics that can last for a long time unless they are are using an device that has documented 5V tolerance on its I/O pins.

There are a multitude of different chips designed with either 5V tolerant inputs or designed to properly level translate from 5V down to 3.3V. Use one of those, or if you want something cheaper that comes with a lower bandwidth, then you can utilize two resistors at each input as a voltage divider to step the 5V down to 3.3V.