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P82B96: When connecting the Sx and Sy of the P82B96 to the B side of the TCA9517, communication is not possible

Shinichi Inoue
Guru 20706 points
Part Number: P82B96
Other Parts Discussed in Thread: TCA9517, , TCA9416

Tool/software:

Dear Specialists,

My customer is evaluatingP82B96 and TCA9517, communication is not possible.

I would be grateful if you could advise.

---

 When I connect the Sx and Sy of the P82B96 to the B side of the TCA9517, communication is not possible.

The GND level at that time rose to 0.8V.

I wonder if the reason it doesn't work is because I connected a device with a buffer function in series.

Could you please introduce a device that can be used instead of the TCA9517.

On the other hand, when I directly connect a 3.3V compatible I2C sensor device to the P82B96,

it works without any problems. (Temperature sensor, acceleration sensor, pressure sensor, etc.)

The GND level does not float.

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Mastermind 33805 points

    Hi Shinichi,

    I suspect the VOL from  Sx / Sy is too high for the TCA device.

    This may be confirmed by removing the 4.7k on the TCA side verifying the GND level reduces below 0.8 V. Although not p2p you may also see TCA9416 with internal pull-ups where all external pull-ups may be removed, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Guru 20706 points

    Hi Michael,

    Thank you for your reply.

    I shared it should be removed pull up resistor of  TCA9517 side for reduce below 0.8V with the customer.

    When i obtain the result,  I'll share the result with you.

    Also, would the TCA9416 you mentioned solve the problem without the need for pull-ups? 

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 33805 points

    Hi Shinichi,

    Usually, two P8 devices are connected in series (similar to the datasheet recommendation) to ensure the Tx / Ty side with the 0.4 V is used as an output. This will fix the VOL concern.

    Switching to TCA9416 will reduce VOL due to the higher value internal pull-ups i.e. smaller pull-ups indicates stronger current for the increased VOL. 

    Removing one of the pull-ups reduces the current for a lower VOL as they seem two parallel pull-ups results to a stronger value.

    Additionally, VOL may be further lowered when the pull-up is removed and the pull-up present is increased, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Guru 20706 points

    Hi Michael,

    Thank you for your reply.

    As you mentioned, the pull-up resistor on the TCA9517 side was removed, but operation did not improve.
    The SCL/SDA B output is split.

    I would like to share the customer's connection diagram and waveforms.

    Please send friendship as this is confidential.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 33805 points

    Hi Shinichi,

    I sent a request.

    To clarify, "operation did not improve", do you mean VOL is still 0.8 V or < 0.8 V but not low enough for VIL spec of the TCA device? Thanks.

    Best Regards,

    Micha