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TCA9517: cannot be connected Bside to B-side

Shu-Cheng LIN
Guru 11785 points
Part Number: TCA9517


Hi Sirs,

Sorry to bother you

We have some power sequence concern so we need to change the TCA9517 IC direction.

But we saw datasheet show 

The TCA9517 cannot be connected Bside to B-side, because of the buffered low voltage from the B-side. The B-side cannot be connected to a device
with rise time accelerators.

Could you help check what risk we connect B side to B side?

 

Our application as below. The second and third TCA9517 B side will connect to Master. Any risk?


We don't saw this description "cannot be connected Bside to B-side" on TCA9617, so could we use TCA9617 for our application?

 

  • 0
    TI__Guru 62920 points

    Hi Shu-cheng,

    Unfortunately it looks like your image didn't post correctly.  If it is important, then please re-post it so that we can review.  Generally, though, communication is unlikely to work properly when the B sides are connected to one another.  The device uses a "VOL" level on its B side that is higher than its "VIL" level.  This means that it doesn't recognize its own low output level as a logic low.  (If it did, it would drive both sides low and never recover.)  You can refer to this application note for more details about how I2C buffers implementing static voltage offsets function:

    http://www.ti.com/lit/an/scpa054/scpa054.pdf

    Is it possible to re-arrange your connections so that the "B" side of one TCA9517 connects to the "A" side of the other TCA9517?

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    Guru 11785 points

    Hi Sirs,

    Thanks for your reply.

    As shown in the figure below, if the VOL of the MASTER is lower than the SVO (VIL) of the two BUFFERs, can TCA9517 be used?

  • 0 in reply to Shu-Cheng LIN
    TI__Guru 62920 points

    Hi Shu-Cheng,

    If the master VOL is below the VIL of the buffer, then low levels will successfully propagate from the master to each slave.  If the VOL of the buffer is below the VIL of the master, then low levels will successfully propagate from each slave to the master.  However, in this case the low levels sent by one slave would not be received by the other slave.  This may be OK depending on the application needs, but I wanted to mention it for your consideration.

    Regards,
    Max