A quick post on how to use the LSF0204 voltage translator for translating either from a 3.3V to a 5V signal or vice versa. Or at least what I did to make it work.

Why am I posting this? Because Google doesn't turn up a 'just do this' result and I had to wade through way too much information to get to a very simple answer.



That's it. That's all you do.

You need pull up resistors when going from 3.3V to 5V. The smaller the resistor the shorter the rise time but a 2.2KOhm resistor is fine for the sub-MHz speed I'm using it for. Texas Instruments recommended a ~330Ohm resistor for a ~16MHz signal when up translating so that should give you a ballpark figure.

It's worth noting that RefB must always be higher than RefA. If you want to translate a 5V signal to a 3.3V signal then your 5V output is connected to any of the Bs and the 3.3V input is connected to any of the As. The other way is the opposite. If translating from a 3.3V signal to a 5V signal then the 3.3V output is connected to any of the As and the 5V input is connected to any of the Bs. No direction select needed.

Apparently the pull up resistors are optional on the 3.3V side. I tried with and without and both worked, they're recommended so I'm guessing it's best to include them.

Texas Instruments have some okay'ish videos on general LSF device usage. The one I found most useful was Up Translation with the LSF Family somewhere around the 2:10 mark.
Nexperia also has a have video Operating Principles of LSF Autosense Translators with a lot of waffle until about 5:30.

A few other things worth noting: if you're using an LSF0102 or LSF0108 you'll need an additional resistor and capacitor to make it work; the LSF0204 includes them internally. The enable pin voltage is relative to RefA but it is 5V tolerant so it's fine to use RefB as the enable.