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FAQ

What is the pull-up resistor value for I2C bus?  Issue Date：2015-04-23

For the standard-mode I2C-bus system, the resistor value Rp in the figure above is determined by the following parameters:

  1. I2C speed;
  2. Supply voltage;
  3. Bus capacitance;
  4. 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 kΩ.

 ( 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.

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Applications:
Function: Peripherals,Connectivity,I2C,Software and Tools,Hardware,Layout

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