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ISO1540: ISO1540 rise time spec

Part Number: ISO1540
Other Parts Discussed in Thread: ISO1640

Hi there,

Why is ISO1540 datasheet without rising time parameter? It seems like there is only falling time parameter(tf1 and tf2). 

Thanks and regards,

Charles

  • Hi Charles,

    Thank you for posting to E2E! Since ISO1540 and ISO1640 are open-collector I/O devices, they can drive LOW signals states as specified by tf1 and tf2, but external circuitry is needed to provide HIGH signal states.

    Rise times of systems using either isolated I2C device will vary based on bus capacitance, pull-up resistances, and other impedances, therefore the I2C standard specifies signal rise and fall times, depending on communication data rates. We do expect our ISO1540 and ISO1640 families of devices to comply with I2C standards when operated within recommended conditions.


    Thank you,
    Manuel Chavez

  • Hi Charles,

    To clarify, I2C signal rise times are simply the time it takes for a line to pull HIGH after the bus releases a pin from LOW. This is dependent solely on the RC time constant between the pull up resistance and capacitance on the bus.

    The ISO1540 and ISO1640 just release the bus, and the time it takes the signal to go HIGH is a result of the bus capacitance and pull up resistance.


    Thank you,
    Manuel Chavez