I am building my first circuit for i2c and the chip I am controlling using an MCU requires a pull-up resistor on SDA and SCL. I am using a voltage divider because my MCU is 5V and I need 3.3V. Does it matter what side of the divider I put the pull-up on? Based on the layout the 3.3V side would be much easier?

 

Pullup to 3.3V, not 5V.

Or switch to a MCU that runs on 3.3V.

If you must use 5V MCU, read this:

http://www.nxp.com/documents/application_note/AN10441.pdf

or buy this:
http://www.ti.com/product/pca9306

 

hi,
If you prefer building your own discrete shifter, this is one option.

https://www.amazon.co.uk/MOSFET-60V...e=UTF8&qid=1470209191&sr=8-38&keywords=bss138

 

I am building my first circuit for i2c and the chip I am controlling using an MCU requires a pull-up resistor on SDA and SCL. I am using a voltage divider because my MCU is 5V and I need 3.3V. Does it matter what side of the divider I put the pull-up on? Based on the layout the 3.3V side would be much easier?

Do you need bidirectional or is one-way good enough?

 

Do you need bidirectional or is one-way good enough?

Don't you need bidirectional for the acknowledge from the slave?

 

Don't you need bidirectional for the acknowledge from the slave?

Sorry, i2c. I had SPI on my brain from another discussion.