I'm working on a system where I have 5V and 3.3V devices that need to be connected via I2C, and I found the following app note to be quite helpful. It uses two inexpensive MOSFETS as level shifters in an odd configuration (the gates are always tied to 3.3VDC, while the sources are connected to the 3.3V I2C lines and the drains are connected to the 5V I2C lines).
Page 10 has the picture of the configuration.
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Any thoughts on this? I thought it was cool.