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TCA9544A: Minimum value of FALL TIME for I2C signals

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Prodigy 90 points
Part Number: TCA9544A

Hello. 

A MIN value is specified for the fall time in FAST MODE of I2C. The fall time is usually very fast and it is difficult to slow it down.

What happens if the fall time is less than the MIN value? Also, please tell me how Cb should be calculated.

Best regards.

  • 0
    Guru 244690 points

    This value is copied from the I²C specification. This limit applies to the system as a whole. When one driver is too strong, the fast edge might result in undershoots and ringing on the bus, which can be interpretet as false clock pulses by other devices. This limit prevents such errors.

    Cb is the total bus capacitance.

    The I²C specification has a pull-up current limit of 3 mA. You will get problems only if you configure the drive strength of the I²C pins for something much larger than this.