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Original question:

TCA4307: How to place this part to use

TCA4307: I2C parallel connections

Yuta Nishie
Genius 4925 points
Part Number: TCA4307
Other Parts Discussed in Thread: TCA9517A, TCA9617B, TCA9548A

Tool/software:

Hi, 

The thread below says "The TCA4307 is capable of driving two I2C segments of 400pF."

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1288764/tca4307-how-to-place-this-part-to-use?tisearch=e2e-sitesearch&keymatch=TCA4307#

Does this mean that I can only connect two I2C in parallel? Or can I connect 3~5 (more than 2) slaves in parallel as shown in the figure below?

Best Regards,

Nishie

  • 0
    Guru 316350 points

    "Segment" means a bus segment; each segment can have many I²C devices.

    In practice, you would use one TCA4307 per hot-plugged card; see figure 8-6.

  • 0
    TI__Mastermind 46703 points

    Hi Nishie,

    TCA4307 is meant for hot-swap applications. It this application as such? 

    Consider stacking buffers such as the TCA9517A or TCA9617B. What are the voltage level requirements at the master, in-between buffers, and at the slaves? 

    Technically speaking, you can connect many buffers in series but you would need to consider the timing implications when doing so. If the bus is heavily loaded, and considering the prop delay of each buffer in series, one might need to reduce the overall data rate in order to have successful I2C communication. 

    Please see this application note

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Genius 4925 points

    Hi Clemens-san, Townsend-san,

    Thank you for your support.

    Hot swap is not required. The applications are as follows, and a buffer is required to connect the boards with a harness.

    ・I want to connect the boards in the enclosure with I2C.
    ・There are 2~5 boards on the slave side, and I want to connect them in parallel.
    ・The power supply voltage is 3.3 V.

    1. I would appreciate it if you could tell me the IC or circuit that can realize the above method.

    2. Also, could you tell me the difference between TCA4307 and TCA9517A/B?

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    TI__Mastermind 46703 points

    Hi Yuta,

    Will only 1 bus segment be active at a time? If so, have you considered using an I2C switch? The TCA9548A might be of interest. 

    The circuit would look like the following: 

    In order for the TCA9548A to work, we would need to know the total amount of parasitic cap loading you plan to drive on each cable length. We would also need to know if more than 1 channel would be active at the same time. 

    If you do need re-drive capability due to long cabling, what is the reasoning for 2 x TCA4307's? Can you use an application similar to this one:

    The master would connect to the A-side of the TCA9617B. The TCA9617B would buffer the master and slave devices. 

    Yuta Nishie said:
    2. Also, could you tell me the difference between TCA4307 and TCA9517A/B?

    TCA4307 is a hot swap buffer with stuck bus recovery. It is used in hot swap applications. This device implements a dynamic offset. 

    TCA9517A is a i2c buffer. It is not hot-swap capable, nor does it have stuck bus recovery. This device implements a static voltage offset. 

    Both devices are capable of separating two 400pF I2C segments totaling for 800pF of re-drive. 

    For more info, see the I2C faq page

    Regards,

    Tyler