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Original question:

PCA9306: There is a step at Low level

PCA9306: There is a step at Low level

user6021663
Prodigy 40 points
Part Number: PCA9306
Thank you for your reply.
When the SCL1, SDA1, SCL2, and SDA2 lines are low, there is a step of about 0.7V.
What should I do to lower the Low level below 0.6V?
Scope shots cannot be submitted.
The circuit diagram is as follows.
  • 0
    Prodigy 40 points
    The circuit diagram is below.
  • 0 in reply to user6021663
    TI__Guru 62920 points

    Hello,

    The voltage increase through the PCA9306 will typically be very small since its switches have very low on-state resistance.  (If you are seeing otherwise, please let us know and we can debug it with you.)  So, in this case the higher "low" voltage is probably present on both sides of the PCA9306 and is being generated by either the CPU or the level shifter.  Many level shifters intentionally use a high "low" level so that they can distinguish between when they are driving low or some other component is pulling the bus low (so that they know which direction data is flowing on the bidirectional bus).  Can you please check the VOL specification of the level shifter to see if it uses some offset voltage that could explain what you are seeing?  Or, if you can provide the part number we can help check it.

    By the way, you can read more about how I2C buffered level shifters work (and why a voltage offset is sometimes used) in this app note:

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

    Regards,
    Max