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TCA4311A, TCA9517, TCA9517A - some questions

Hirotaka Matsumoto
Guru 27525 points
Other Parts Discussed in Thread: TCA9517A, TCA4311A, TCA9517, TCA4311

Hi all

Would you mind if we ask TCA4311A, TCA9517 and TCA9517A?

<Question>
About the internal circuit of these devices, which do these devices have ’NMOS Series Switch type’ or ’Basic Structure of an NMOS/PMOS Parallel Switch type’?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Genius 16430 points

    Matsumoto-san,

    Thanks for the question.

    1) The TCA4311 is more like a series switch type, but has additional circuitry around it (rise time accelerators, precharge circuits, etc). Fundamentally, it is a series switch that connects both sides.

    The TCA9517 and TCA9517A have both sides isolated from each other, and use a parallel switch to ground to transmit 0s. See below simplified internal example of TCA9517[A]

    2) The difference between TCA9517 and TCA9517A is merely the difference between VOL and VIL on the B side. The TCA9517A has a smaller VOL-VIL range. Typically, we recommend that customers go to the TCA9517 (non-A) unless they see some issue where a slave is unable to pull voltage low enough to trip the B side comparator. The advantage is that the TCA9517 has a larger margin for noise, meaning less likely to get false 0s in some situations.

  • 0 in reply to Jonathan Valdez
    Guru 27525 points

    Jonathan san

    Thank you for your prompt reply!

    We'd like to confirm on point.

    TCA4311A is not both ’NMOS Series Switch type’ or ’Basic Structure of an NMOS/PMOS Parallel Switch type’, isn't it?

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Genius 16430 points
    Matsumoto san,

    The TCA4311A is a series switch type with additional circuitry around it. There are current sources on the lines which activate at edge detection, so it depends on if you consider a rise-time accelerator as a parallel switch.
  • 0 in reply to Jonathan Valdez
    Guru 27525 points

    Jonathan san

    Thank you for your reply.
    Ok we got it.

    Kind regards

    Hirotaka Matsumoto

  • 0 in reply to Jonathan Valdez
    Mastermind 8420 points
    Hi Jonathan-san,

    Allow me ask you 5 questions as below about the difference between TCA9517 and TCA9517A?

    Q1) The difference is just "VILC" value, correct?
    That is to say, datasheet Page 6, VILC value,
    TCA9517A : 0.45V (TYP)
    TCA9517 : 0.4V (TYP)
    I could not fine any other difference without package.
    If you know any other differece, please let me know.

    Q2) Figure 6, page 9
    There describes that the level of "INPUT SDAB, SCLB" is "0.4V". (Figure 6)
    I suppose that this level seems to be 0.45V not 0.4V... What do you think of this?

    Q3) The meaning of "0.45V" of VILC
    According to datasheet page 1, there are description that
    "a higher contention level threshold (=0.45V) allows connections to slaves which have weaker pulldown ability".
    Sorry, I do not understand well about the meaning of this sentence.
    Could you tell me the meaning, especially "weaker pulldown ability"?

    Q4) Errata
    Let me confirm again the difference.
    TCA9517A is not a bug-fixed device of TCA9517, correct?
    So there is not the document like "errata" about TCA9517, right?

    Q5) One user case
    One customer has a data communication problem with TCA9517.
    There sometimes happens "data error".
    The detailed situation is still unknown yet but could you tell me your feeling if the sitation is improved
    in case of using TCA9517A not TCA9517?

    Thank you for your support.
    Best Regards,
  • 0 in reply to Takumi Suzuki1
    TI__Genius 16430 points
    Takumi-san,

    1) The only difference is the VILC value, yes.

    2) You are correct, the value here should reflect the value in the datasheet's electrical specification table. A lot of times, the images in datasheets get re-used if the parts are very similar.

    3) "Weaker pulldown ability" means that the RON of the internal pull-down FET is higher than a 'normal' slave. THe result is that when a slave with a weaker pulldown ability tries to pull the bus low, instead of hitting 0V, the bus may only drop to 0.4V. This device adds another 50 mV to add some margin for slaves with the inability to pull the voltage below 0.4V.

    4) You are correct. The TCA9517A is not a bug fix. It is merely a slight spec change. We actually recommend that the TCA9517 non-A be used in most cases, unless you have a slave on the bus which is weak. The reason is that with a slightly lower VILC, the TCA9517 has a higher noise margin than the TCA9517A (if the voltage bounces between VILC and VOL).

    5) I would be happy to help debug your issue. It is unlikely that the A version would improve the situation unless the issue is a result of a slave with a higher RON internal-pulldown. Can you post some pictures of the failed I2C communication on a scope? We can tell a lot about the I2C bus from scope shots.
  • 0 in reply to Jonathan Valdez
    Mastermind 8420 points
    Hi Jonathan-san,

    Thank you very much for your answer.
    I understood.

    Best Regards,