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Original question:

TCA9546A: Regarding pullup voltage on the output I2C channels

TCA9546A: TCA9546A channel length application

Brian Chan
Expert 6690 points
Part Number: TCA9546A


Tool/software:

Hi Team

do you have any recommendation about the channel for TCA9546A in I2C application?

customer plan to use 400kHz and 10k pull up resistor

BRs

Brian

  • 0
    Guru 317480 points

    The speed of rising edges is limited by the R-C low-pass filter formed by the pull-up resistor and the total bus capacitance. I²C limits the capacitance to 400 pF and the pull-up current to 3 mA (or 6 mA for large buses near 400 pF, if the devices allow this).

    In general, 3 mA is no problem for a 200 pF bus at 400 kHz.

    With a switch like the TCA9546A, the pull-up resistors on all simultaneously enabled channels act in parallel. How many are there in your application?

    A rough estimate of capacitance is 10 pF per device, and 1 pF per cm of trace.

    You should start with the needed bus length, and then size the pull-ups for that.