I2C Bus: Level Shifting

I2C buses are not limited to a defined voltage. In some applications different I2C reference voltages are used for different ICs. Sometimes it is necessary to have all of them sharing the same bus. To be able to recognize what a logical zero and logical one is, a level-shifter is necessary.

Different to most interfaces the I2C bus does not have a dedicated direction, e.g. multiple devices may pull the SCL line to ground.

The causes serious problems building level shifters since they have to take care of moving a request from one side to the other one and vice versa without introding back coupling and oscillation. The basic idea to handle this is to limit the bandwith on the bus. This give poor transfer-rates of course.

A basic idea on how to build a level shifter

Commercial level shifters as Levii and Optii are using different approaches providing higher bandwiths. Optii has some additional, outstanding feature: it separates the I2C buses galvanically, so two I2C buses can be logically connected but electrically insulated.





	Level Shifting
I2C Bus I2C Primer Addressing Auto Increment Clock Stretching Fast Mode Fast Mode Plus High Speed Mode I2C Interface Level Shifting Multi-Master References Repeated Start Condition Single-Master Slave Standard Mode Termination Voltage Level PMBus SMBus Imprint	I2C buses are not limited to a defined voltage. In some applications different I2C reference voltages are used for different ICs. Sometimes it is necessary to have all of them sharing the same bus. To be able to recognize what a logical zero and logical one is, a level-shifter is necessary. Different to most interfaces the I2C bus does not have a dedicated direction, e.g. multiple devices may pull the SCL line to ground. The causes serious problems building level shifters since they have to take care of moving a request from one side to the other one and vice versa without introding back coupling and oscillation. The basic idea to handle this is to limit the bandwith on the bus. This give poor transfer-rates of course. A basic idea on how to build a level shifter Commercial level shifters as Levii and Optii are using different approaches providing higher bandwiths. Optii has some additional, outstanding feature: it separates the I2C buses galvanically, so two I2C buses can be logically connected but electrically insulated.