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TCA9517: How to use TCA9517

Y.Ottey
Mastermind 6145 points
Part Number:

Dear TI Team

Our customers are considering TCA9517.

I would like you to tell us about the following contents.
1. Is the I2C output of TCA9517 correct in recognition that both SDA and SCL are open drain outputs?
 (From this, we think that pull-up resistors are required for the SDA and SCL lines.)

2. Do VCCA and VCCB always have to be VCCA <VCCB?

3. Our customers are considering the following two configurations.
Is there any problem in using TCA9517?
(For Case2, there is a circuit similar to the data sheet Figure.9.)


Regards,

Y.Ottey

  • 0
    Guru 317390 points

    1. The TCA9517 does not have any internal pull-up mechanism, so you indeed need pull-up resistors on all bus segments.

    2. The web site says VCCA ≤ VCCB, but the datasheet does not mention such a restriction. The datasheet of the improved TCA9617B device does mention it, so I guess the web site is correct.

    3. If VCCA ≤ VCCB is required, then this is not allowed. If you can use 3.3 V in the middle, it would be possible to use two TCA9803‍s.

  • 0 in reply to Clemens Ladisch
    Mastermind 6145 points

    Dear Ladisch


    Thank you for your reply.


    Dear TI Team

    I would like the TI Team to answer this question,
    so I would be grateful if you could get a reply as soon as possible.

    Regards,
    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Guru 74292 points

    Clemens,

    Thank you for the help as usual.

    Y.Ottey,

    Our I2C expert has been made aware of this thread and will be getting back to you by end of day11/30/2020 CST time. Thank you for your patience while the US is on holiday.

    Regards, 

  • 0 in reply to Eric Hackett
    Mastermind 6145 points

    Hi Eric

    Thank you for your reply.

    I have received a request from our customers for an early response.
    Therefore, I would be grateful if you could reply as soon as possible.

    Regards,

    Y.Ottey

  • 0
    TI__Guru 73991 points

    Y.Ottey said:

    Part Number: TCA9517

    Dear TI Team

    Our customers are considering TCA9517.

    I would like you to tell us about the following contents.
    1. Is the I2C output of TCA9517 correct in recognition that both SDA and SCL are open drain outputs?
     (From this, we think that pull-up resistors are required for the SDA and SCL lines.)

    Correct. The TCA9517 does not drive the line high by itself, it requires an external pull up.

    2. Do VCCA and VCCB always have to be VCCA <VCCB?

    The device was designed to operate in this manner and the electrical parameters were tested with this condition. Technically the device will still operate if you have VccA>VccB however we cannot guarantee the electrical parameters will be correct anymore (I would expect shifts such as longer prop delays and potentially lower ViLs, ect.)

    3. Our customers are considering the following two configurations.
    Is there any problem in using TCA9517?
    (For Case2, there is a circuit similar to the data sheet Figure.9.)

    Case 1 looks okay.

    Case2 looks like you violating the RoC on VccB. VccB states the lowest operating condition is 2.7V. Under the conditions of the second 9517, I would expect the electrical parameters to no longer be true and you would be using the device out of spec.

    Regards,

    Y.Ottey

  • 0
    Guru 317390 points

    For case 2, you can replace the TCA9517 with the P82B96 (see section 10.2.5 of the datasheet).

  • 0 in reply to Clemens Ladisch
    Mastermind 6145 points

    Dear TI Team

    Thank you for your reply.

    Our customer is considering changing Case 2 to the following configuration. What about this configuration?
    (I don't think it's possible to connect B ports to each other.)

    Also, is there any other good device for the following configuration?
    (The two TCA2517s are 1-2 meters apart, and I've heard they want the TCA2517 to be used as a buffer.)

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Guru 73991 points

    TCA9517 does not work when you have B sides of both devices connected together. 

    As clemen's pointed out, if you are trying to communicate through a cable, then using the P82B96/P82B715 may be a suitable approach.

    -Bobby

  • 0 in reply to BOBBY
    Mastermind 6145 points

    Hi BOBBY

    Thank you for your reply.

    I understand that I can't connect B ports to each other.

    I'm thinking of proposing to our customers a configuration that uses two P82B96 or P82B715.
    If you want to use the same configuration as Case 2, is it possible to set VCC = 5.3V?

    Also, I confirmed P82B96 and P82B715, but it seems that the only difference is the recommended range of VCC. Which is better?

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    Mastermind 6145 points

    Hi BOBBY

    I have received a request from our customers for an early response.

    In addition, it is asked if there is any problem with the following configuration.
    I think that there is no problem because it is connected from B port to A port and the configuration is VCCA = VCCB, but what about?

    Regards,
    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Guru 73991 points

    Hi Y..Ottey,

    The concern I see is that you are outside of the recommended operating conditions now since 70% of 5.3V = 3.7V. The ViH on B side isn't being met. That being said, I believe the device would still be functional and the main affect of this would be that the supply current may be higher from the device since you are not fully driving the line high on B side.

    -Bobby

  • 0 in reply to BOBBY
    Mastermind 6145 points

    Hi BOBBY

    Thank you for your reply.

    I haven't answered the following questions I posted earlier.
    Could you please tell me this answer?

    ”I'm thinking of proposing to our customers a configuration that uses two P82B96 or P82B715.
    If you want to use the same configuration as Case 2, is it possible to set VCC = 5.3V?

    Also, I confirmed P82B96 and P82B715, but it seems that the only difference is the recommended range of VCC. Which is better?”


    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Guru 53575 points

    Hi Y.Ottey,

    Sorry for the delay. I'll try to help while Bobby is out.

    Though they share similar part names and serve similar functions, P82B96 and P82B715 use different methods to accomplish bus extension. That said, one is not inherently "better" than the other, but one may suit some designs better than others. I'll briefly touch on both of these to help showcase the differences.

    P82B96 operates as a buffer, red-driving received signal on the opposite side of the device - the main difference from other buffers is the drive strength of the high-capacitance side, able to drive much higher loads and cables than would be allowed in typical I2C systems. This device also is capable of provide galvanic isolation because it separates TX and RX lines (which can be connected together without latching). 
    P82B96:

    P82B715 instead operates as a current amplifies, allowing the original signal driver to sink a small portion of the current needed to drive the high-capacitance bus or cable low. Because the original signal driver is physically connected to the extended bus, no isolation is possible and the signal driver is still responsible for sinking a portion of the extended bus current. 

    P82B715:

    I hope this helps your understanding of these two devices. Let me know if you have any other questions.

    Regards,
    Eric Schott