I2C extender on long cables
Created: Feb 18, 2015
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The P82B715 is a bipolar IC intended for application in IC-bus and derivative bus systems. It can be used to increase the total connected capacitance of an I2C-bus system to around 3000pF. It can drive IC-bus signals over long cables to approximately 50 meters or 3000pF.
The P82B715TD I2C buffer was designed to extend the range of the local I2C bus out to 50 meters. This application note describes the results of testing the buffer on several different types of cables to determine the maximum operating distances possible.
Different types of cable were tested. The results were based on the cable runs in a low electrical noise environment. If reliable operation is desired in a high electrical noise environment, shielded cable must be used. For "short" runs, flat cable with every other conductor grounded, seems to provide a good, low capacitance medium for I2C transmission, otherwise, the shielded audio cable seemed to provide the best price or performance. For long runs, it is desirable to have a separate power supply at each end of the cable, and the shield or ground wire will provide a common reference between the two supplies.