• State TI Thinks Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 3 answers
  • Subscribers 34 subscribers
  • Views 500 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TCA9617B: Please review the block diagram for the combination of TCA9617B and TCA9546A

louis.chang
Prodigy 240 points
Part Number: TCA9617B
Other Parts Discussed in Thread: TCA9546A, , TCA9544A, TCA9545A, TCA9509, TCA9803

Hi Sirs

Please review the block diagram for the combination of TCA9617B and TCA9546A 

Another question as below

TCA9546A is switch type, TCA9544A is mux type, If I plan to connect SD0 to SD3 to the equipment with the same address, and these 4 equipment could be work simultaneously, which one I should use?

Thank you

  • 0
    TI__Mastermind 39946 points

    Hi Louis,

    The output low voltage (VOL) on the TCA9617B's B side will be about 0.52V. Having this at the input of the TCA9545 will only result in a higher VOL after the TCA9546A's outputs when the 1V8 MCU is driving a low. Its important to note the VILC requirement on B-side of the TCA9617B by ensuring the VOL of the TCA9545A is lower then the VILC requirement of the TCA961B. 

    At a top level, the TCA9546A allows for one or more channels to be enabled at a given time whereas TCA9544A will only allow a certain channel to be enabled at a time. In this case, the TCA9546A may be more suitable since you would require all 4 channels to be enabled at once.

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Prodigy 240 points

    Hi Jack

    Based on your reply, here is my understanding, please correct me if I am wrong

    1. Vol of TCA9617B B side will be about 0.52V, and maximum VIL of TCA9546A is 0.3 x VCC (0.3 x 3.3 = 0.99), so it would be no problem, right?

    2. You are saying the low level output of TCA9546A would be higher due to TCA9617B VOL (about 0.52V) , what high the value is? > 0.52V?

    3.  You are saying that need to ensure VOL of the TCA9545A should lower than the VILC requirement of the TCA961B.

         what is maximum value of Vol for TCA9545 (TCA9546A)?  and what is VILC requirement on B-side of the TCA9617B?  

    It seems many constraints for this I2C buffer, if keep using TCA9546A, could you base on this block diagram to suggest another I2C buffer? (current source based I2C buffer rather than this SVO I2C buffer) 

    Thank you

  • 0 in reply to louis.chang
    TI__Mastermind 39946 points

    Hey Louis,

    1. Yes this is correct, it won't be a problem for the TCA9546A's VIL, however it is recommended to also check the VOL of the TCA9546A since the TCA9546A will not redrive the output low voltage. Here is an example case that we want to avoid if possible.

    2. It will be dependent on the pullups you used on the I/Os of the TCA9546A. Weaker pullups used will result in lower VOLs, but also impacts rise time negatively. See this app note for pullup calculation for your I2C bus. 

    3. Similar to the above, the VOL of the switch/mux would depend on the pullups used as well as the current sunk by your receiver on the 3V3 side. 

    What is the data rate of your I2C signals? If 400KHz and above, you may see the TCA980x series buffers, or the TCA9509. These I2C buffers have an internal current source (TCA9509 on the A side, TCA980x on the B side) to sense which side of the device is driving low. Note that external pullups are no longer needed on the same side as the internal current source. 

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Prodigy 240 points

    Hi Jack

    Thank you for your reply.

    After internal discussion, we plan to change buffer to TCA9803, but now we have two topologies, the main difference is voltage, please help to check these two block diagrams works or not? And potential risk?

    1. all 1.8V

    2. transfer to 3.3V via TCA9803

  • 0 in reply to louis.chang
    Guru 316440 points

    The TCA9546A is a passive switch, so the pull-up resistors are visible on the other side, so you must not connect it to the TCA9803's B side.

    Both topologies will work if you change the TCA9803's A and B sides (so that there are no pull-ups on the MCU bus).

  • 0 in reply to Clemens Ladisch
    Prodigy 240 points

    Hi Clemens

    Due to some reasons, the pull-ups on the MCU bus must exist, we can't remove it.

    So just swap TCA9803's A and B, (B side toward to MCU) should not work properly.

    Any suitable component I can use between MCU and TCA9803 like this?

    If no, I can only back to use TCA9617B, but few questions still want to check

    Please see the diagram below, due to TCA9617B B side can only support 2.2V to 5.5V, so I fix to 3.3V

    the right side of TCA9546A could probably be 1.8V, so I can only use VCC of TCA9546A= 1.8V

    But I found VIL of TCA9546A becomes 0.54V, it seems lower than the VOL of TCA9617B, it probably can't work correctly, right? 

    So now if two new block diagrams can't be used, can you suggest how to solve this I2C series connection?

    here is the design requirement

    a. MCU :1.8V voltage rail with pull-ups

    b. Slave : In the output of TCA9546A and 1.8V voltage rail and pull-ups already

    c. TCA9546A should be used.

    d. Need a buffer between TCA9546A and MCU

    Thank you

  • 0 in reply to louis.chang
    Prodigy 240 points

    Hi Clemens

    By the way, you are saying change the TCA9803's A and B sides (so that there are no pull-ups on the MCU bus).

    Should pull-ups at A side of TCA9803? (between TCA9803 and TCA9546A)

    Thank you

  • 0 in reply to louis.chang
    Guru 316440 points

    Yes, the TCA980x always needs pull-ups on its A side (except when connected to another TCA980x's B side).