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TCA9539: fall time is less than 20ns

Perry Chen
Prodigy 10 points
Part Number: TCA9539

Tool/software:

Hi Sir,

Based on TCA9539 specification, minimum I2C fall time is 20ns+0.1*(total capacitance of one bus line).

But I check my device, I2C fall time ls less than 20ns, if I use RC dealy, it will impact rise time.

Is fast I2C fall time (less than 20ns) acceptable?

Thanks.

  • +1
    Guru 316880 points

    This value is copied from the I²C specification. The TCA9539 itself (or any other I²C input) does not care; the I²C specification has this limit to prevent ringing on the lines.

    Check the I²C signals (at the TCA9539's pins) with an oscilloscope. If there is no ringing at falling edges, then everything is OK.

    Does your device have pins with configurable drive strength? In general, I²C should use no more than 3 mA.

  • 0
    TI__Mastermind 47668 points

    Hi Perry,

    Please see Clemens' answer. 

    Regards,

    Tyler