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TCA9517: Vol of TCA9517

shiwei luan
Intellectual 750 points
Part Number: TCA9517
Other Parts Discussed in Thread: TCA9803,

From datasheet Section 7.5 "Electrical Characteristics", the minimal VOL is 0.45V.

Why there  is offset at output? Isn't it supposed to be close to 0V as close as possible to provide more noise margin?

Please help to provide some details. 

Thank you.

  • 0
    TI__Guru 73761 points
    Hello Shiwei,

    The voltage offset is there to prevent the part from latching after the line is released (is allowed to be pulled back to high). As long as the VOL remains lower than 0.3*Vcc, we can ensure our device will read a low and therefore does not need to be as close to ground as possible.

    -Bobby
  • 0
    TI__Prodigy 255 points

    Hi Shiwei,

    To add to Bobby's response, we have an I2C buffer that provides a much lower VOL spec than the TCA9517 - take a look at the TCA9803. This device has an improved architecture to eliminate the need for a static voltage offset, which allows the VOL to be much closer to 0V .

    Max VOL of TCA9803 is 0.26V - see electrical characteristics from the datasheet below.

    Regards,

    Kaitlyn

  • 0
    TI__Mastermind 23326 points
    Hello Shiwei,
    Here is a previous post that explains how the static voltage offset works and why you need it on a buffer. Let me know if you have any other questions after reading the post. NOTE: E2E is a searchable forum and you could have entered your search term in the search box above. You would have found posts similar to this:

    e2e.ti.com/.../2275729 do you need static voltage offset#2275729

    -Francis Houde
  • 0 in reply to Kaitlyn Mazzarella
    Intellectual 750 points

    Thank you, Kaitlyn. Do you have I2C buffer ICs with 5V power supply plus low VOL ?

  • 0 in reply to shiwei luan
    TI__Mastermind 23326 points
    Hello Shiwei,
    The other options is to connect the side without the static voltage off-set to the device that has a low VIL. Then connect the other side to the opposite side assuming both don't have the low VIL requirements.
    -Francis Houde