What is the pull-up resistor value for I2C bus?
Posted: 27 Mar 2017, 13:47
For the standard-mode I2C-bus system, the resistor value Rp in the figure above is determined by the following parameters:
I2C speed;
Supply voltage;
Bus capacitance;
The number of connected devices (input current + leakage current).
The supply voltage (VDD) and the maximum output LOW level determine the minimum value of pull-up resistor Rp.
For example, a supply voltage of 4.5V, VOL= 0.4 V and Rp is 4.7 k?.
( 4.5 - 0.45 ) / 4700 = 8.617 mA < Sink current.
The maximum bus capacitance of the value Rp limits is approximately 400 pf (capacitive load), calculated by cut-off frequency (1/2 * pi * Rp * Cb), to meet the requirement that the maximum tr (SCL/SDA rising time) is 300 ns.
I2C speed;
Supply voltage;
Bus capacitance;
The number of connected devices (input current + leakage current).
The supply voltage (VDD) and the maximum output LOW level determine the minimum value of pull-up resistor Rp.
For example, a supply voltage of 4.5V, VOL= 0.4 V and Rp is 4.7 k?.
( 4.5 - 0.45 ) / 4700 = 8.617 mA < Sink current.
The maximum bus capacitance of the value Rp limits is approximately 400 pf (capacitive load), calculated by cut-off frequency (1/2 * pi * Rp * Cb), to meet the requirement that the maximum tr (SCL/SDA rising time) is 300 ns.