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ISO7742-Q1: I2C isolation

Piotr F.
Intellectual 2670 points
Part Number: ISO7742-Q1
Other Parts Discussed in Thread: ISO1640-Q1, ISO7741-Q1, ISO7742

Hello Team,

My customer is looking at app note https://www.ti.com/lit/an/slyt403a/slyt403a.pdf?ts=1669725353435 and intend to use ISO7742-Q1 uni-directional digital isolator for I2C interface - similarly to the application described on the app note.

They wonder:

  • is there any I2C pull-up limitation ?
  • what would be bandwidth limitation (is there any? ISO7742-Q1 datarate is 100Mbps)
  • 0
    TI__Mastermind 21575 points

    Hello Piotr, 

    Thank you for considering ISO7741-Q1. If you need two bidirectional I2C channels, then please consider using ISO1640-Q1 which is our isolated I2C interface solution that may be better suited for your application. 

    • is there any I2C pull-up limitation?
      • The value of an I2C pull-up resistor is system dependent and heavily related to bus capacitance. Please refer to section 9.2.2 Detailed Design Procedure of the ISO164x datasheet and I2C Bus Pull-Up Resistor Calculation for more information on calculating pull-up resistors for I2C
    • what would be bandwidth limitation (is there any? ISO7742-Q1 data rate is 100Mbps)
      • While using ISO7742 as per the application note, the BW limitations will be from the bus capacitance as well. The R and C values of the system need to be calculated to keep the I2C rise and fall times compliant with the standard.
      • Please refer to the input capacitance of ISO774x from the datasheet and use the rest of the component capacitances and trace and series resistances to estimate effective R and C value for the system. This can then be used to estimate BW.

    I hope this help. Please follow up if you have more questions. 

    Best,

    Andrew