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TCA9517: TCA9517 Connection and Levels

Martin Kirstein1
Prodigy 80 points
Part Number: TCA9517
Other Parts Discussed in Thread: TCA9800

Hi,

I am using the TCA9517 on a 3.3V SM Bus (both sides). The Master is currently Connected on Side B, ans other Slaves are on Side A (all 3.3V).

The Datasheet example has the Master placed on Port A. But there is a text in the datasheet that the master can be connected on either sides. Is there a problem with the master on side B ?

Also I am seeing a offset on low levels for signal and clock on B Side of about ~600mV. This is not recongnized as low for the SMBUS device on side A. I am tried to increase the pullups but I can not get this low level down to ~0V. What causes this issue?

EDIT:

One more thing I need to say is that the A Side (that goes "outside") is connected with a pullup to the VCCB Side (internal) because both voltages should be identical. The Datasheet wants this to be connected to the VCCA side, but I do not have this exact voltage. Any problems here ?

Thanks

  • +1
    Guru 317480 points

    The I²C protocol is bidirectional, so electrically, there is no difference between masters and slaves.

    The high-level voltage can be anywhere between 0.7 × VCC and 5.5 V.

    The B-side drivers of the TCA9517 indeed have an offset; see section 9.3.3 of the datasheet.

    If you want a buffer without offset, use the TCA9800 (which has different restrictions).