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SN65HVS883: 3,3V at de-bounce Pins DB0/DB1

Lutz Naumann
Expert 6110 points
Part Number: SN65HVS883

Hi Team,

can we use a 3,3V MCU controlling the de-bounce pins DB0/DB1? I would assume we have the same 200kOhm pull up resistors to 5V internally like a the other logic pins. When connecting an MCU driving the 3,3V the internal pull up would try to lift even further to 5V. The MCU may have ESD cells that starts conducting and pulls the voltage slightly down. So it will end up somewhere between 3,3V to 5V. The leakage current would be acceptable. Could you please let me know what the Logic-High threshold max is that we need to guarantee? We could not find this figure in the datasheet.

It is important to understand is a additional level translator is absolutely needed or if we can interface with a3,3V Logic directly.

many thanks

Lutz

  • 0
    TI__Mastermind 46317 points

    Hi Lutz,

    Please see the Debounce function table  I have attached above. 

    The device works by checking if the pin is grounded or open. The MCU can ground the line and it can float the line. That being said the high level logic input for this device is 2V. It doesn't specify what pins that applies to - but this is a digital pin as it refers to this table as the logic inputs. The digital high threshold for this device is 2V. I don't see any problem with having an MCU float the line for "open" and ground it for ground because this should be within the operating specs. However if this worries you in the application a switch can be implemented  that the MCU can control on each debounce pin  - essentially either grounding it or truly leaving it "open" - I don't think this is necessary but it would alleviate all risk to do that. 

    If you have any other questions please let me know!

    Best,

    Parker Dodson

  • +1
    TI__Expert 6110 points

    Thanks Parker,

    for more robustness in rugged environment we recommend to pull the DB0, DB1 pin to 5V if needed. I would not want to have them floating in our case. With the before statement in the datasheet I would expect a week pullup to be inside, that is enforced by the external voltage to make sure one stays above the logic threshold. Means the pin should be happy when externally driven to a voltage. With 2V max for the logic high we would be perfectly fine with 3,3V.

    many thanks

    Lutz