Electronic – Cheapest way to translate 5V SPI signal to 3V SPI


I have a MCU that operates at 5V, and a display that recommends a 3V logic level. They are connected via SPI that can operate up to 1.5Mhz. What is the best way and the cheapest way (not necessarily the same), to convert the 5V to 3V? The SPI connection is one way (SCK, MOSI, CS only; no need for the LCD to communicate to the MCU, so the translation is from 5V to 3V only).


Best Answer

As Matt said, the simplest is a resistor divider. The drawback is that it will slow edges a little. You'll probably be OK with the 1 kΩ and 2 kΩ he shows but it would be a good idea to check the waveform with a scope.

When speed is a issue, like it most likely would be if you were running the SPI bus at 10 MHz, then a explicit level converter would probably be better. These chips have two power supplies and usually a direction input, which you could permanently tie in one direction in your case.

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