Bi-directional level shifter for I2C-bus and other systems.

Bi-directional level shifter for I2C-bus and other systems.

With a single MOS-FET a bi-directional level shifter circuit can be realised to connect devices with different
supply voltages of e.g. 5 Volt and 3.3 Volt to one I2C-bus system. The level shifter can also isolate a bus
section of powered-down devices from the I2C-bus, allowing the powered part of the I2C-bus to operate in a
normal way.
The level shifter can also be used in other bus systems or point to point connections for level shifting and/or
isolation.

Present technologies for integrated circuit with clearances of 0.5 mm and less, limit the maximum supply voltage
and consequently the logic levels for the digital I/O signals. To interface these lower voltage circuits with
existing 5 Volt devices a level shifter is needed. For bi-directional bus systems as e.g. the I2C-bus, such a level
shifter must be bi-directional, without the need of a direction control signal. With only one appropriate MOS-FET
for each bus line the desired level shifting with automatic direction control can be done. The levels may have a
vast range, depending on the used MOS-FET, e.g. down to 2 Volt at the “Lower voltage” side and up to 10
Volt or more at the “Higher voltage” side of the level shifter.
An additional function of the level shifter is that it can isolate a powered-down section in a bus system, without
obstructing the powered part. Another feature is the protection of the “Lower voltage” section against high
voltage spikes at the “Higher voltage” section, as long as the MOS-FET can withstand this spikes.

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