SLVA787 September   2016 LM8330 , LM8335 , P82B715 , P82B96 , PCA9306 , PCA9306-Q1 , PCA9515A , PCA9515B , PCA9518 , PCA9534 , PCA9534A , PCA9535 , PCA9536 , PCA9538 , PCA9539 , PCA9543A , PCA9544A , PCA9545A , PCA9546A , PCA9548A , PCA9554 , PCA9554A , PCA9555 , PCA9557 , PCF8574 , PCF8574A , PCF8575 , PCF8575C , TCA4311A , TCA6408A , TCA6416A , TCA6418E , TCA6424A , TCA9509 , TCA9517 , TCA9517A , TCA9534 , TCA9534A , TCA9535 , TCA9538 , TCA9539 , TCA9539-Q1 , TCA9543A , TCA9544A , TCA9545A , TCA9546A , TCA9548A , TCA9554 , TCA9554A , TCA9555 , TCA9617A , TCA9617B , TCA9800 , TCA9801 , TCA9802 , TCA9803

 

  1.   Choosing the Correct I2C Device for New Designs
    1.     Trademarks
    2. 1 Introduction
    3. 2 I/O Expander Applications
      1. 2.1 RESET Pins
      2. 2.2 Internal Pullups
      3. 2.3 Address Pins
      4. 2.4 Level Shifting
    4. 3 I2C Switches
      1. 3.1 Control Register
      2. 3.2 Hot Insertion Supported
      3. 3.3 Address Pins
      4. 3.4 Level Shifting
    5. 4 I2C Buffers
      1. 4.1 Pull-Up Resistors
        1. 4.1.1 Static Voltage Offset
        2. 4.1.2 Level Shifting
    6. 5 I2C Voltage Translation

4.1 Pull-Up Resistors

Pull-up resistors need to be connected from the I2C lines to the supply voltage to enable communication. In regards to the capacitive load on the bus, there is a max resistance value associated with the bus capacitance, while the minimum value is determined from the maximum allowed sink current (per I2C slave devices on the bus), offset voltage, and supply voltage.(1)(1)Once the thresholds are determined, the system designer must determine if a stronger pullup is required to account for the capacitance. With a stronger pullup (lower resistance value), more current will be used to make rise times faster for SCL and SDA and ensure that I2C rise time specifications are met. For more information on pull-up resistors on the I2C bus, refer to I2C Bus Pullup Resistor Calculation (SLVA689).

1. lost the footnote?

fig06_slva787.gifFigure 7. Heavily-Loaded Bus Requiring I2C Buffer
fig06a_slva787.gifFigure 8. I2C bus utilizing I2C buffer, which allows more slave devices