4 I²C Buffers

In compliance with the I²C specification, the maximum capacitive load of the bus is limited to 400 pF. Once the capacitance is exceeded, the rise times on the I²C bus may violate the timing requirements. With an I²C buffer and repeater (buffer/repeater), slave device's capacitances can be isolated on each side of the buffer to have two I²C segments, each capable of up to 400 pF each.

Buffers/repeaters allow for more slave devices to be added to the I²C bus in applications that have a heavily-loaded I²C bus. In applications utilizing the I²C bus, slave devices and trace length are major contributors to the total capacitance of the I²C bus. A quick way to estimate the amount of bus capacitance is to account about 10 pF per slave device. If the total capacitance nears the maximum load of 400 pF, there could be issues with the rise time falling out of the I²C specification.

The end of this section (Figure 10) shows a selection chart for narrowing down buffer selection in I²C applications that exceed capacitance loads.