Same I2C bus but with more than four ADG728

Hi 

We are trying to expand our test setup from 8 channels to 12 channels, currently, we have four ADG728 to connect all 8 channels together for one of the tests. We are at four ADG728 and what would be the best way to expand our application to have 12 channels? We would also need the 12 channels to be connected together for one of the tests. Any other part that may have more channels or more bits for the I2C address? 

Do you have any newer switch matrix similar to ADG728 or next gen of ADG728 that has more channels or more bits for I2C address?

Thank you, 
Jason

  • 0
    •  Analog Employees 
    on Sep 15, 2021 8:23 AM

    Hi Jason,

    I moved your thread to the Switches/Multiplexers community. Someone here will be able to help you.

    Best regards,

    Mark

  • 0
    •  Analog Employees 
    on Sep 17, 2021 11:32 AM

    Hi Jason,

    The ADG728 is the largest mux (8:1) x 1 in our Switch/Mux product portfolio with an I2C interface.

    Yes the best way to expand your application is to use multiple ADG728 devices on the same bus.

    If you need all 12 channels to be connected together for one test, is it possible to connect the outputs of the two devices together and then turn on 12 channels from both ADG728 devices at the same time ?

    Please let me know your thoughts,

    Regards,

    Kevin

  • Hi Kevin, 

    Thanks for your reply. Yes, it's possible to connect the output of the two devices together to turn on 12 channels from both devices. But in the meantime, we would need eight ADG728 connected to the same I2C bus.

    To solve the address conflicting issue with more than four devices, I plan to use an I2C bus switch and have four ADG728 with four different addresses in one group. The I2C bus switch will allow me to turn on one group of ADG728 at a time. Usually, I can find the I2C bus switch in four or eight channels and it will solve the address conflicting issue, I believe.

    Another approach is to have a pair of P type of FET and to turn on/off four ADG728 at a time, it needs two digital lines to control the clock and data. To control two groups, we will need four digital lines. 

    Which method do you think is better? Do you see any other recommended method from ADI to overcome the four address limit in ADG728? Do you have any app notes on this topic? 

    Thank you, 
    Jason

  • +1
    •  Analog Employees 
    on Sep 23, 2021 1:18 PM in reply to JasonSong

    Hi Jason,

    Apologies for the delay in responding.

    I think both methods should work if implemented correctly.

    The I2C switch seems like the simplest approach, as it only requires one switch and two digital lines.

    I don't have any App notes on this topic specifically, but if you want to send schematic diagrams of your two possible solutions for review, please do.

    Regards,

    Kevin