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ISO1541: To know the maximum distance of the I2C cable that it supports between ISO1541 and slave device

Subha Angusamy
Prodigy 40 points
Part Number: ISO1541
Other Parts Discussed in Thread: ISO1540

Hi Sir,

     We are using  ISO1541 device for isolating I2C compatible communication between Master (MCU) and slave (NFC Board), we need to know the maximum distance of the I2C cable that it supports between ISO 1541 isolator IC and NFC board 

Thanks & Regards,

A.Subha

  • 0
    TI__Mastermind 49445 points
    Hi Subha,

    Welcome to TI E2E Forum and thank you for showing your interest in ISO1541.

    The maximum length of cable that can be connected between two I2C devices depends on the device load capacitance spec and capacitance of the cable. I believe you are trying to isolate the I2C interface of MCU on MCU board before it is connected to the NFC board. In such a case, Side1 (SDA1/SCL1) of ISO1541 should be connected to MCU while Side2 (SDA2/SCL2) should be connected to the I2C bus/cable which connected to NFC board at the other end. Please make sure the I2C I/O electrical specifications of MCU are compatible with ISO1541 Side1 electrical specifications.

    On Side2, ISO1541 supports a maximum load capacitance of 400pF. With a cable having capacitance of 100pF/m, you can connect upto 4m of cable to be able to support datarate upto 1Mbps. I am assuming the NFC board I2C interfacing device input capacitance is <10pF, please consider this capacitance also into account to calculate the max length of cable that it can support.
    After you make sure ISO1541 can drive the cable length defined, please also make sure the slave is also able to drive the cable. The input capacitance of ISO1541 is 7pF typical on both sides.

    I am assuming you do not intend to implement clock stretching in your application, if you do intend then please make sure you use ISO1540 instead of ISO1541 to be able to support clock stretching. Thanks.


    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    TI__Prodigy 730 points
    Hi Koti, Subha also wanted to understand the EMC and noise considerations and the effects of increasing the cable length as well. Would you be able to comment on the same.
  • 0 in reply to Rahul Ramachandran
    Prodigy 40 points
    Dear Sir,
    We need to know the EMC consideration and noise effects on increasing the I2C cable length to about 2 meters on side 2.

    Thanks & Regards,
    A.Subha
  • 0 in reply to Subha Angusamy
    TI__Mastermind 49445 points
    Dear Subha, Rahul,

    I have responded to your other E2E post that discusses about EMC considerations for ISO1541. Please do have a look at that post. I have provided the link below for the post. Thanks.

    e2e.ti.com/.../2968319


    Regards,
    Koteshwar Rao