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Looking for cross reference for isl33002

Marek Roszko
Intellectual 380 points
Other Parts Discussed in Thread: TCA4307, TCA9416

I am looking for a I2C bus buffer similar to the TCA4307, however it needs a special function that's in the ISL33002 we currently use.

The ISL part has "pull-down accelerators" which in our particular application are critical due to weak pull-down strength of the driving micro. In fact it's funny most buffers seem focused on pull-up acceleration and bus buffering capacitance but completely overlooking that a micro ultimately has to sink that capacitance as well :/

Does TI have a part like this?

Here is an image showing the NMOS pulldowns in their block diagram

  • 0
    Intellectual 380 points

    Actually, does the TCA4307 function as a true buffer like this? I can't tell because the first page diagram is drawn like a buffer while the later diagrams are just drawn as switches

  • 0
    TI__Guru 73971 points
    Marek Roszko said:
    In fact it's funny most buffers seem focused on pull-up acceleration and bus buffering capacitance but completely overlooking that a micro ultimately has to sink that capacitance as well :/

    The reason for this is because the pull down driver's Ron is typically much smaller than the pull up resistor is resulting in a smaller RC constant. Most I2C systems that are heavily loaded on capacitance are looking to meet the rise time requirements.

    Marek Roszko said:
    The ISL part has "pull-down accelerators" which in our particular application are critical due to weak pull-down strength of the driving micro.
    Marek Roszko said:
    Actually, does the TCA4307 function as a true buffer like this? I can't tell because the first page diagram is drawn like a buffer while the later diagrams are just drawn as switches

    TCA4307 is an I2C buffer in the sense that it redrives the signal (separating capacitance from both sides and the current as well unlike a pass FET switch). The big advantage to using a device with a rise time accelerator is the external pull up resistor can now be sized much larger (higher value) so the micro will see a much lower IoL thus the VoL would lower as well. Normally, pull down accelerators aren't necessary since the RC constant between the load capacitance and the Ron of the open drain driver (like the micro) would be low enough that it meets the fall time requirements for I2C. (I've never seen a system where the fall time was actually violated).

    Marek Roszko said:
    Does TI have a part like this?

    The only device I'm aware of in TI's portfolio with pull down accelerators are TCA9617 and TCA9416. (I did hear a design mention 9517 had it but it's not in the datasheet and I would need go back and ask if it really infact does have it).

    If you have any follow up questions, please let me know.

    -Bobby