5v to 3.3v - SPI Tranlation

Someone posted an article a while back which shows how to translate a SPI bus (or likely any bus really) from 3.3v to 5v so that one bus could work at both levels using only 1 fet and 1 resistor per line. I've been trying to find this document, but I have been unsuccessful. I have found Microchips 3.3 - 5v Tips 'n Tricks document, but I couldn't find what I was looking for exactly in there. I think I've replicated the circuit, but I wanted to compare it.

Are you talking about 1 pull-up resistor connected to the "output high voltage supply" and one pull-down FET driven by the input line? (Will only work for unidirectional busses...so for SPI it is fine, but not for I2C).

See if this fits your requirement.

dknguyen said:

Are you talking about 1 pull-up resistor connected to the "output high voltage supply" and one pull-down FET driven by the input line? (Will only work for unidirectional busses...so for SPI it is fine, but not for I2C).

Click to expand...

yes, thats what I'm talking about. When I saw it, I didn't realize that it was unidirectional. The SPI bus I have implemented uses the same line to transmit and receive on so thats probably why it wasn't working out in my head.

The schematic posted by eblc1388 will work bi-directionally for I2C. It will not be fast enough for SPI though. For SPI I would use something like this:

Interface - Voltage Level Translation - TXB0104 - TI.com

Or these

https://www.electro-tech-online.com/custompdfs/2008/10/MC74VHC1G125-DPDF.pdf
https://www.electro-tech-online.com/custompdfs/2008/10/MC74VHC1GT125-DPDF.pdf
https://www.electro-tech-online.com/custompdfs/2008/10/MC74VHC1GT50-DPDF.pdf