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TCA9617B: I2C connection

Part Number: TCA9617B
Other Parts Discussed in Thread: PCA9306, TCA9509

Hi Team

I have some question about TCA9617B.

SDA will not be output correctly when used with the following configuration.
It becomes an intermediate potential like a waveform.
Is there a problem with such a configuration?
Also, do you know the cause that can be inferred from this material?

Best Regards,
Ishiwata

  • Hey Ishiwata,

    It looks like the device is configured incorrectly. B side of TCA9617B has a static voltage offset and when you put two B sides together (#1 and #2 B sides) you will find that B side requires the signal to go below 0.4V to correctly pass a low however B side generates a VoL of 0.54V so you may not see low signals propagate correctly.

    The datasheet mentions this here:

    There are two ways to fix this:

    1. Redesign your board so that you flip one of the TCA9617Bs and then use a level shifter between the two (PCA9306?).

    2. Remove the pull up resistors on side #1 and replace TCA9617B #1 with TCA9509

    Thanks,

    -Bobby

  • Hi Bobby

    Thank you for your answer.

    I have an additional question.

    As a basic question, as in the following configuration

    Is it possible to convert the level from A (5 V) to B (3.3 V)?

    Best Regards,

    Ishiwata

  • Hi Ishiwata,

    For voltage level translation, which your figure seems to indicate, VCCA would need to be lower than VCCB. May I ask the design requirement for the 5V supply level in between the two TCA9517Bs?

  • Hey Ishiwata-san,

    The configuration you've drawn will not work because unit 2 has VccA side larger than VccB side. Our TCA9617B requires VccB>=VccA.

    Thanks,

    -Bobby

  • Hi Bobby

    I appreciate your support.
    I undersood.

    I would like to confirm your previous proposal.

    "1. Redesign your board so that you flip one of the TCA9617Bs and then use a level shifter between the two (PCA9306?)."

    When using PCA9306, the description of VOL and VIL was not on the data sheet.
    Please tell me the value.

    Best Regards,
    Ishiwata
  • Hey Ishiwata,

    "PCA9306, the description of VOL and VIL was not on the data sheet."

    PCA9306 is only a level-shifter (not a buffer), so it does not re-drive the signal. This means PCA9306 will basically just pass whatever VoL is on oneside to the other with a minor shift up. For example, if VoL is 300mV on side 1, side 2 will see a VoL of 300mV plus some extra voltage due to loss across Rdson.

    For ViL, assuming you are using the voltage level translation mode of PCA9306 correctly then it will begin to pass a low when you are below Vcc1.

    Thanks,

    -Bobby

  • Hi Bobby - san

    Thank you for contacting me.
    In your explanation I was able to understand.
    I appreciate your support.

    Best Regards,
    Ishiwata

  • Hi Bobby

    I understood very much about the contents of the last time.
    I appreciate your support very much.

    Sorry. There are additional questions from customers.
    Customers want to know the reasons for the waveform that will be the midpoint potential (Red frame) in the case of the following configuration.


    The above waveform monitors input SCLA/SDAA and output SCLB/SDAB of TCA9617B(1).
    When SDA is low level, SCLB is output about 0.7 V.

    Customers want to know the 0.7 V mechanism of this SCLB.
    Is it caused by current or voltage detection on B side of TCA 9617B(2)?


    Best Regards,
    Ishiwata

     

  • Hey Ishiwata,

    "Is it caused by current or voltage detection on B side of TCA 9617B(2)?"
    Likely the static voltage offset of TCA9617B#2, for a short time #1 is able to drive #2 below 0.4V so #2 may be responding to that short pulse by driving low as well. We need scopeshots of Both unit 1 and unit 2 SCL lines when we see this event.

    Thanks,
    -Bobby
  • Hi Bobby

    Thank you for your reply
    Do you know why midpoint potential (Red frame) is output from this circuit and waveform?

    Best Regards,
    Ishiwata
  • Hey Ishiwata-san,

    My last reply discusses why I think there is a large step. I would need scope shots one all 3 points to confirm.

    Thanks,

    -Bobby

  • Hi Bobby-san

    I'm very sorry that your connection will be late.
    I will check with customers. About the waveform

    Thank you for your support.

    Best Regards,
    Ishiwata