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P82B96: I2C communication over long distance with two P82B96 chips

Anand Badiger
Prodigy 10 points
Part Number: P82B96

Tool/software:

We have 7Z SoM based board, from that we are planning to interface a microcontroller (probably STM32) with I2C where 7z SOM is master and STM32 is slave. One catch here is the two boards will be connected with a 4meter long cable. Can you please suggest how can we interface the same? 

I came across the chip P82B96 for the same but when i looked into the forum, i could see lot of issue people were facing. It would be helpful if you can tell whether to go with this chip for my application or any other chip suggestion? If same/different chip, what precautions to be considered so that it should work just fine. Or is it better to go with I2C to UART/RS232 conversion then transmit over cable then convert it back to I2C?

Thanks 

Anand B

  • 0
    Guru 316510 points

    If you wanted to convert between I²C and a more robust protocol like RS-422, you would need a chip like the P82B96.

    Do you really require I²C? Protocols with unidirectional signals like UART or SPI would be much easier to handle over 4 m.

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    Yes, need I2C only. The 7z SoM board is already designed and we have some authentication chips which will use I2C which need to be interfaced.

    I didn't get your thought on P82B96.

  • 0 in reply to Anand Badiger
    Guru 316510 points

    I²C is bidirectional. The P82B96 can split one bidirectional signal (Sx or Sy) into two unidirectional signals (Tx/Rx or Ty/Ry).

  • 0
    TI__Mastermind 47128 points

    Hi Anand,

    I think something along the lines of this reference design for converting I2C to a differential signal (in this example using CAN transceivers). 

    However, this adds more complexity to the problem, and is this specific solution for more very long cables. 

    If you require I2C, I think two P82B96's interfaced to eachother would be the simplest solution. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 10 points

    Hi Tyler,

    Thank you for the details. 

    One thing i observed is there are number of cases where designer has reported that they are facing issues while using P82B96 chip. Wanted to know any precautions to be taken care if i go forward with two P82B96 chips for my application?

    Regards

    Anand B

  • 0 in reply to Anand Badiger
    TI__Mastermind 47128 points

    Hi Anand,

    Common use case problems is not tuning the PU resistors properly or running into an issue where the VOL of the buffer is not compatible with their I2C target / controller device. 

    The vol table shows the output voltage on Sx/Sy side is quite large. The user must determine if this is compatible with the master/slave input VIL voltage. 

    Regards,

    Tyler