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ISO7710: Can the output coexist on an open-drain bus?

Scott Brenneman
Genius 3265 points
Part Number: ISO7710
Other Parts Discussed in Thread: SN74LVC1G07, ISO1640

Hello,

I'm having trouble determining if the output of the ISO7710 can be compatible with a shared interrupt signal populated by a number of active-low, open-drain devices.  I see that the output has a push/pull architecture, but that its polarity is programmable. Please help clarify how it works.

Thanks,

Scott

  • +1
    TI__Genius 11075 points

    Hello,

    Thank you for your question.

    Since the ISO7710 can have a HIGH and LOW output states and the open-drain output type has High Impedance or LOW output states, they can not be connected together. This is because the ISO7710 can output a HIGH state while the open-drain device can output a LOW state, which can cause a short from VCC to ground.

    This also applies to other digital isolators as well and is not limited to the ISO7710. While open-drain output devices can be connected together, push-pull output devices should not be connected together as it would cause damage to the device.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya Vittal
    Genius 3265 points

    I was afraid of that.  Okay, thank you for clarifying.

    Scott

  • 0 in reply to Scott Brenneman
    TI__Mastermind 24885 points

    Scott,

    I don't have full clarity as to the system you are trying to implement, but since you are looking at a digital isolator, I assume that your signal is unidirectional? 

    If so, a simple open drain buffer at the output of the digital isolator could easily solve this problem. For example, an SN74LVC1G07 could be put at the output of the digital isolator to functionally make the output open drain. 

    Alternatively, if you are looking for a bidirectional open-drain signal (such as what is used for I2C), we have I2C Isolators that provide an isolated open-drain interface that may be applicable to your system.

    For example, the ISO1640 could be used. 

    Hope this helps, and let us know if you need further recommendations.

    Best,
    Michael

  • 0 in reply to Michael J Schultis
    Genius 3265 points

    Hi Michael,

    It's unidirectional, so I already added an open-drain buffer after the output.

    Thanks,
    Scott

  • 0 in reply to Scott Brenneman
    TI__Mastermind 24885 points

    Sounds good, thanks Scott!

    Let us know if we can help further.