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TCA9803: TCA9803 parallel connection

Hidaka
Prodigy 145 points
Part Number: TCA9803
Other Parts Discussed in Thread: PCA9306
Hi E2E
The I2C bus described in the attached file cannot access slave device A.
When board C is removed, slave device A can be accessed.
Change the level shifter of "C" as a measure to prevent access.
We are considering TCA9803 with a small VOL as a candidate.
Is it possible to connect TCA9803 in parallel?

Also, I would appreciate it if you could introduce an I2C level shifter
that can be connected in parallel.
best regards
  • 0
    Prodigy 145 points

    Hi E2E

    Since the insert file was not included, we will resend it.
    Best Regards

  • 0 in reply to Hidaka
    TI__Guru 73331 points

    Hello,

    My guess is that the passive pass FET architecture of the NSTX is causing additional IoL through them from the other pull up resistors resulting in higher VoL levels that the slaves cannot accept as a logic low. The Ron of the passive pass FET may also be adding additional shifts to the VoL.This means you would need an I2C buffer with level translation features (not a level translator).

    TCA980x can be used in parallel as long as B side of TCA980x is not connected to (1) any other static voltage offset sides of of a buffer (like another B side of TCA980x for example), (2) level shifters, (3) switches.

    So in your set up, you should be able to replace NTSX2102 with TCA980x as long as you make the A side connect the 1.8V rail and remove the pull up resistors on the 3.3V rail (TCA980x has its own internal current source to supply the I2C rail with a logic high).

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 145 points

    bobby

    Thank you for your reply.

    Is it OK to think that it should work even if the TCA980x in the figure is replaced with PCA9306?

    Our team has a track record of using the PCA9306, and the PCA9306 has a small package lineup, so it would be very helpful if the PCA9306 could be used.


    Hidaka

  • 0 in reply to Hidaka
    TI__Guru 73331 points

    Hi Hidaka,

    PCA9306 is not an I2C redriver, it is purely an I2C level shifter, If the problem previously was due to a high VoL due to the pass FET architecture of the previous device allowing a larger IoL then PCA9306 would not solve the problem. Since I do not know 100% what was generating the problem, I can't say for certain if PCA9306 would work.

    If your planning on building a prototype/test board. I would probably place a DNP PCA9306 in parallel to TCA980x to verify if the PCA9306 would work. Alternatively you could provide scopeshots of the previous problem and we can try to isolate the problem so we can say with certainty that PCA9306 could be used.

    -Bobby