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TCA9416: TCA9416

Ranjeet Malhotra
Prodigy 85 points
Part Number: TCA9416
Other Parts Discussed in Thread: TCA9617B, TCA39306

Tool/software:

Hi - we are looking to use a TCA9416 for one of our application to provide isolation on SMBUS between our Target and a host. The SMBUS could run at 1 MB/sec.

The target supply I2C levels could be more or less than the host I2c levels - hence we need a device where there is no requirement that VCCA <= VCCB.

Is it possible to comment on suitability of this device. The trace length for the I2C lines could be upto 30 cms.

Thanks

regards, Ranjeet

  • 0
    TI__Mastermind 37293 points

    Hi Ranjeet,

    The TCA9416 is technically not an I2C buffer/re-driver. It does not provide isolation/separation between a target and host. What I mean by this is that the pull-up resistance and bus capacitance on each side of the translator will appear in parallel since TCA9416 uses FET-based architecture between its input & output. 

    The TCA9416 does include internal pull-up resistors and RTA/FTA's for assistance in the rising and falling edge (rise-time accelerators & fall-time accelerators). 

    The RTA's and FTA's do help with larger cap loads by speeding up the rise and fall times during I2C transactions, however, this is not the same architecture as a buffer such as the TCA9617B where the I2C signal enters some input buffer, and the signal is reproduced on the output through a separate current sink driver. 

    For 30 cms of trace, I usually estimate about 1 pF / 1 cm of trace which means the loading is 30 pF from trace alone. Considering that the Target and host probably contribute ~ 10pF input cap, the total estimated loading is ~ 50pF which is well below the 550 pF budget required by fast mode+ I2C speeds (up to 1 MHz).

    I don't think you need the RTA and FTA from TCA9416. Have you considered switching to a more simple level translator such as the TCA39306? When RTA and FTA are combined with long traces which introduce more inductance to the system, it can be likely that the I2C lines have over/under shoots. If TCA9416 is to be used, I would include footprints for series dampening resistors on the I2C lines on both sides of the TCA9416. 

    Regards,

    Tyler