I2C Bus Pullup Resistor Calculation
I2C Bus Pullup Resistor Calculation
Pullup resistor calculation for I2C interface is a commonly asked question. In this application note we show how to use simple equations for this calculation.
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1 Introduction
I2C communication standard is the mostly widely used inter-chip communication standard in today’s electronic systems. It is an open-drain/open-collector communication standard which implies integrated circuits (IC’s) with different voltage supply rails can be connected for communication. Pullup resistors need to be connected from the I2C lines to the supply to enable communication as shown in Figure 1. The pullup resistors pull the line high when it is not driven low by the open-drain interface. The value of the pullup resistor is an important design consideration for I2C systems as an incorrect value can lead to signal loss. In this article we show the simple equations for the pullup resistor calculation which the system designer can use to do quick calculations for their design.
Figure 1. Application Example Showing I2C Communication Between the Different IC's on a System and With Pullup Resistors on I2C Bus