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ISO7841: input voltage threshold and minimum input voltage

Part Number: ISO7841

Hi,

I would like to know the inputs threshold voltage of the ISO7841. In the datasheet is written under the "Recommended Operating Conditions" that:High-level input voltage  Min=0.7 × VCCI. 

Under "Electrical Characteristics" is written that the Input threshold voltage hysteresis is 0.1xVCCI but is not mentioned the voltage threshold.

Is the Input voltage threshold equal to VCCI*0.5? If yes, the minimum input voltage should be 0.55VCCI (VCCI*0.5+VCCI*0.1*0.5). Where am I wrong?

Thank you 

Antonello

  • Hi Antonello,

    Thanks for bringing your inquiry to E2E!

    The ISO7841 uses CMOS logic thresholds. What is considered a high or a low are in bands. So a high is between Vcc1 and 0.7*Vcc1. A low is between GND1 and 0.3*Vcc1. I quickly put together diagram to show this: 

    If your signal is within the green band at the top, it is considered a valid HIGH.If the signal is within the green band at the bottom, it is a valid LOW. The middle grey area is undefined. 

    I hope that clears things up. Please let me know if you have any questions. 

    Best regards, 

    Dan

  • In reply to Dan Kisling:

    Hi Dan,

    thank you for the fast reply. the answer is clear but I have still one question. If the level voltage for high and low signale are the ones pointed from you and written under the "Recommended Operating Conditions"  in the datasheet, what is the "Input threshold voltage hysteresis"  (0.1xVCCI) written in the "Electrical Characteristics" chapter?

    thank you

    Antonello

  • In reply to Antonello Castigliola:

    Hi Antonello,

    I agree that this is confusing, and doesn't seem consistent with our other digital isolator datasheets. I have made a to see if we can improve this with a datasheet update to make it more like the ISO7741 datasheet.

    Would something like this make more sense to you?

    Best regards, 

    Dan

  • In reply to Dan Kisling:

    Hi DAN,

    I prefer to delete the Input threshold voltage hysteresis because, in my opinion, it is redundant and confusing. In my opinion, the two thresholds, indicated like in the ISO7741 datasheet, better describe the behaviour of the component without any misunderstanding.

    thank you

    Antonello

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